Search Results

Search found 8001 results on 321 pages for 'empty'.

Page 39/321 | < Previous Page | 35 36 37 38 39 40 41 42 43 44 45 46  | Next Page >

  • How do I create an empty Django formset using modelformset_factory?

    - by nbolton
    I'm creating a formset, but it seems to populate it with all of the existing data in the table for that object. I can't figure out how to start with a blank formset; the only way seems to be to delete all of the data from the table, but clearly this isn't an option. I will post code if necessary (but there's lots of it, so knowing what is relevant is tricky).

    Read the article

  • How do I prevent a pair of XMLEvent[Reader|Writer] from splitting empty tags into start+end tags?

    - by java.is.for.desktop
    Hello, everyone! I have an understanding problem of how the following code works: XMLInputFactory xif = XMLInputFactory.newFactory(); XMLOutputFactory xof = XMLOutputFactory.newFactory(); XMLEventReader reader = xif.createXMLEventReader(/* ... */); XMLEventWriter writer = xof.createXMLEventWriter(/* ... */); writer.add(reader); The method writer.add([some reader]) reads all events from reader and writes them consequently. Sadly, following happens: The input <root><c/></root> gets transformed to <root><c><c/></root> I know, from XML point of view, these are equal trees, but not for a human ;) What can I do to get the same output? FYI: I need a XMLEvent[Reader|Writer] pair later to filter "XML events".

    Read the article

  • check if a tree is complete standard ml

    - by aizen92
    I want to make a function in standard ml that checks if a tree is complete or not, the function somehow works, but its giving me the wrong type and a warning of non-exhaustive cases The tree code: datatype 'data tree = EMPTY | NODE of 'data tree * 'data * 'data tree; fun isComplete EMPTY = true | isComplete (NODE(x, y, z)) = if (x = EMPTY andalso z <> EMPTY) orelse (x <> EMPTY andalso z = EMPTY) then false else true; Now the above function's type is: ''a tree -> bool but the required type is 'a tree -> bool The warning I'm having is: stdIn:169.8 Warning: calling polyEqual stdIn:169.26 Warning: calling polyEqual stdIn:169.45-169.47 Warning: calling polyEqual stdIn:169.64-169.66 Warning: calling polyEqual stdIn:124.1-169.94 Warning: match nonexhaustive NODE (x,y,z) => ... What is the problem I'm having?

    Read the article

  • Hibernate saveOrUpdate fails when I execute it on empty table.

    - by Vladimir
    I'm try to insert or update db record with following code: Category category = new Category(); category.setName('catName'); category.setId(1L); categoryDao.saveOrUpdate(category); When there is a category with id=1 already in database everything works. But if there is no record with id=1 I got following exception: org.hibernate.StaleStateException: Batch update returned unexpected row count from update [0]; actual row count: 0; expected: 1: Here is my Category class setters, getters and constructors ommited for clarity: @Entity public class Category { @Id @GeneratedValue(strategy = GenerationType.AUTO) private Long id; private String name; @ManyToOne private Category parent; @OneToMany(fetch = FetchType.LAZY, mappedBy = "parent") private List<Category> categories = new ArrayList<Category>(); } In the console I see this hibernate query: update Category set name=?, parent_id=? where id=? So looks like hibernates tryis to update record instead of inserting new. What am I doing wrong here?

    Read the article

  • Is it good to put a &nbsp; inside an empty <td>?

    - by jitendra
    If this is the structure: <table cellspacing="0" cellpadding="0"> <tr> <td>I don't need anything here, should I always put a &nbsp; here?</td> <td>item </td> </tr> <tr> <td>model</td> <td>one</td> </tr> <tr> <td>model</td> <td>two</td> </tr> <tr> <td>model</td> <td>three</td> </tr> </table> How will a screen reader read a blank td? Is it semantically correct?

    Read the article

  • Wrap a list to add an empty row for UI binding.

    - by TheSean
    I am binding a List to a UI Control. My list does not contain a blank row, but I need to add one to allow the user to select blank. However, I'm using the same list in other parts of the application (users can edit/add/delete items) where it doesn't make sense to show a blank row. My idea is to create a wrapper around the list which adds a blank row just for the UI. The wrapper would hold a reference so that updates to the list (from other parts of the app) would be reflected in UI without any extra work. I have tried a few different ways, but nothing has worked out for me yet. Can anyone solve this problem?

    Read the article

  • What is a truly empty std::vector in C++?

    - by RyanG
    I've got a two vectors in class A that contain other class objects B and C. I know exactly how many elements these vectors are supposed to hold at maximum. In the initializer list of class A's constructor, I initialize these vectors to their max sizes (constants). If I understand this correctly, I now have a vector of objects of class B that have been initialized using their default constructor. Right? When I wrote this code, I thought this was the only way to deal with things. However, I've since learned about std::vector.reserve() and I'd like to achieve something different. I'd like to allocate memory for these vectors to grow as large as possible because adding to them is controlled by user-input, so I don't want frequent resizings. However, I iterate through this vector many, many times per second and I only currently work on objects I've flagged as "active". To have to check a boolean member of class B/C on ever iteration is silly. I don't want these objects to even BE there for my iterators to see when I run through this list. Is reserving the max space ahead of time and using push_back to add a new object to the vector a solution to this?

    Read the article

  • How to select first empty value option in a select menu??

    - by alex
    Hi there, The following always preselects the last option, but i like the first option to be preselected? <select name="filter"> <option value="" selected>Make a choice</option> <option value="1">1</option> <option value="3">3</option> <option value="7">7</option> <option value="">all</option> </select> even with the first selected?? Can this be done??

    Read the article

  • How to remove .zip file in c on windows? (error: Directory not empty)

    - by ExtremeBlue
    include include include include "win32-dirent.h" include include include define MAXFILEPATH 1024 bool IsDirectory(char* path) { WIN32_FIND_DATA w32fd; HANDLE hFindFile; hFindFile = FindFirstFile((PTCHAR)path, &w32fd); if(hFindFile == INVALID_HANDLE_VALUE) { return false; } return w32fd.dwFileAttributes & (FILE_ATTRIBUTE_DIRECTORY); } int RD(const char* folderName) { DIR *dir; struct dirent *ent; dir = opendir(folderName); if(dir != NULL) { while((ent = readdir(dir)) != NULL) { if(strcmp(ent->d_name , ".") == 0 || strcmp(ent->d_name, "..") == 0) { continue; } char fileName[MAXFILEPATH]; sprintf(fileName,"%s%c%s", folderName, '\\', ent->d_name); if(IsDirectory(fileName)) { RD(fileName); } else { unlink(fileName); } } closedir(dir); //chmod(folderName, S_IWRITE | S_IREAD); if(_rmdir(folderName) != 0)perror(folderName); } else { printf("%s <%s>\n","Could Not Open Directory.", folderName); return -1; } return 0; } int main(int argc, char* argv[]) { if(argc < 2) { printf("usage: ./a.out \n"); return 1; } //RD(argv[1]); //_mkdir("12"); //_mkdir("12\\34"); //_rmdir("12\\34"); //_rmdir("12"); char buf[0xff]; sprintf(buf, "unzip -x -q -d 1234 1234.zip"); system(buf); RD("1234"); //unlink("D:\\dev\\c\\project\\removeFolder\\Debug\\1234\\56\\5.txt"); //unlink("D:\\dev\\c\\project\\removeFolder\\Debug\\1234\\56\\6.txt"); //unlink("D:\\dev\\c\\project\\removeFolder\\Debug\\1234\\1_23.zip"); //unlink("D:\\dev\\c\\project\\removeFolder\\Debug\\1234\\4.txt"); //_rmdir("D:\\dev\\c\\project\\removeFolder\\Debug\\1234\\56"); //_rmdir("D:\\dev\\c\\project\\removeFolder\\Debug\\1234"); return 0; } Archive: 1234.zip inflating: 1234/4.txt inflating: 1234/56/5.txt inflating: 1234/56/6.txt inflating: 1234/1_23.zip

    Read the article

  • Null pointer to struct which has zero size (empty)... It is a good practice?

    - by ProgramWriter
    Hi2All.. I have some null struct, for example: struct null_type { NullType& someNonVirtualMethod() { return *this; } }; And in some function i need to pass reference to this type. Reason: template <typename T1 = null_type, typename T2 = null_type, ... > class LooksLikeATupleButItsNotATuple { public: LooksLikeATupleButItsNotATuple(T1& ref1 = defParamHere, T2& ref2 = andHere..) : _ref1(ref1), _ref2(ref2), ... { } void someCompositeFunctionHere() { _ref1.someNonVirtualMethod(); _ref2.someNonVirtualMethod(); ... } private: T1& _ref1; T2& _ref2; ...; }; It is a good practice to use null reference as a default parameter?: *static_cast<NullType*>(0) It works on MSVC, but i have some doubts...

    Read the article

  • What is the proper way to test is variable is empty in a batch file, If NOT "%1" == "" GOTO SomeLabe

    - by blak3r
    I need to test if a variable is set or not. I've tried several techniques but they seem to fail whenever %1 is surrounded by quotes such as the case when %1 = "c:\some path with spaces". IF NOT %1 GOTO MyLabel // This is invalid syntax IF "%1" == "" GOTO MyLabel // Works unless %1, otherwise fatally kills bat execution IF %1 == GOTO MyLabel // Gives an unexpected GOTO error. According to this site. These are the support IF syntax types. So, I don't see a way to do it. IF [NOT] ERRORLEVEL number command IF [NOT] string1==string2 command IF [NOT] EXIST filename command

    Read the article

  • ASP.NET Podcast Show #148 - ASP.NET WebForms to build a Mobile Web Application

    - by Wallym
    Check the podcast site for the original url. This is the video and source code for an ASP.NET WebForms app that I wrote that is optimized for the iPhone and mobile environments.  Subscribe to everything. Subscribe to WMV. Subscribe to M4V for iPhone/iPad. Subscribe to MP3. Download WMV. Download M4V for iPhone/iPad. Download MP3. Link to iWebKit. Source Code: <%@ Page Title="MapSplore" Language="C#" MasterPageFile="iPhoneMaster.master" AutoEventWireup="true" CodeFile="Default.aspx.cs" Inherits="AT_iPhone_Default" %> <asp:Content ID="Content1" ContentPlaceHolderID="head" Runat="Server"></asp:Content><asp:Content ID="Content2" ContentPlaceHolderID="Content" Runat="Server" ClientIDMode="Static">    <asp:ScriptManager ID="sm" runat="server"         EnablePartialRendering="true" EnableHistory="false" EnableCdn="true" />    <script type="text/javascript" src="http://maps.google.com/maps/api/js?sensor=true"></script>    <script  language="javascript"  type="text/javascript">    <!--    Sys.WebForms.PageRequestManager.getInstance().add_endRequest(endRequestHandle);    function endRequestHandle(sender, Args) {        setupMapDiv();        setupPlaceIveBeen();    }    function setupPlaceIveBeen() {        var mapPlaceIveBeen = document.getElementById('divPlaceIveBeen');        if (mapPlaceIveBeen != null) {            var PlaceLat = document.getElementById('<%=hdPlaceIveBeenLatitude.ClientID %>').value;            var PlaceLon = document.getElementById('<%=hdPlaceIveBeenLongitude.ClientID %>').value;            var PlaceTitle = document.getElementById('<%=lblPlaceIveBeenName.ClientID %>').innerHTML;            var latlng = new google.maps.LatLng(PlaceLat, PlaceLon);            var myOptions = {                zoom: 14,                center: latlng,                mapTypeId: google.maps.MapTypeId.ROADMAP            };            var map = new google.maps.Map(mapPlaceIveBeen, myOptions);            var marker = new google.maps.Marker({                position: new google.maps.LatLng(PlaceLat, PlaceLon),                map: map,                title: PlaceTitle,                clickable: false            });        }    }    function setupMapDiv() {        var mapdiv = document.getElementById('divImHere');        if (mapdiv != null) {            var PlaceLat = document.getElementById('<%=hdPlaceLat.ClientID %>').value;            var PlaceLon = document.getElementById('<%=hdPlaceLon.ClientID %>').value;            var PlaceTitle = document.getElementById('<%=hdPlaceTitle.ClientID %>').value;            var latlng = new google.maps.LatLng(PlaceLat, PlaceLon);            var myOptions = {                zoom: 14,                center: latlng,                mapTypeId: google.maps.MapTypeId.ROADMAP            };            var map = new google.maps.Map(mapdiv, myOptions);            var marker = new google.maps.Marker({                position: new google.maps.LatLng(PlaceLat, PlaceLon),                map: map,                title: PlaceTitle,                clickable: false            });        }     }    -->    </script>    <asp:HiddenField ID="Latitude" runat="server" />    <asp:HiddenField ID="Longitude" runat="server" />    <script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1/jquery.min.js%22%3E%3C/script>    <script language="javascript" type="text/javascript">        $(document).ready(function () {            GetLocation();            setupMapDiv();            setupPlaceIveBeen();        });        function GetLocation() {            if (navigator.geolocation != null) {                navigator.geolocation.getCurrentPosition(getData);            }            else {                var mess = document.getElementById('<%=Message.ClientID %>');                mess.innerHTML = "Sorry, your browser does not support geolocation. " +                    "Try the latest version of Safari on the iPhone, Android browser, or the latest version of FireFox.";            }        }        function UpdateLocation_Click() {            GetLocation();        }        function getData(position) {            var latitude = position.coords.latitude;            var longitude = position.coords.longitude;            var hdLat = document.getElementById('<%=Latitude.ClientID %>');            var hdLon = document.getElementById('<%=Longitude.ClientID %>');            hdLat.value = latitude;            hdLon.value = longitude;        }    </script>    <asp:Label ID="Message" runat="server" />    <asp:UpdatePanel ID="upl" runat="server">        <ContentTemplate>    <asp:Panel ID="pnlStart" runat="server" Visible="true">    <div id="topbar">        <div id="title">MapSplore</div>    </div>    <div id="content">        <ul class="pageitem">            <li class="menu">                <asp:LinkButton ID="lbLocalDeals" runat="server" onclick="lbLocalDeals_Click">                <asp:Image ID="imLocalDeals" runat="server" ImageUrl="~/Images/ArtFavor_Money_Bag_Icon.png" Height="30" />                <span class="name">Local Deals.</span>                <span class="arrow"></span>                </asp:LinkButton>                </li>            <li class="menu">                <asp:LinkButton ID="lbLocalPlaces" runat="server" onclick="lbLocalPlaces_Click">                <asp:Image ID="imLocalPlaces" runat="server" ImageUrl="~/Images/Andy_Houses_on_the_horizon_-_Starburst_remix.png" Height="30" />                <span class="name">Local Places.</span>                <span class="arrow"></span>                </asp:LinkButton>                </li>            <li class="menu">                <asp:LinkButton ID="lbWhereIveBeen" runat="server" onclick="lbWhereIveBeen_Click">                <asp:Image ID="imImHere" runat="server" ImageUrl="~/Images/ryanlerch_flagpole.png" Height="30" />                <span class="name">I've been here.</span>                <span class="arrow"></span>                </asp:LinkButton>                </li>            <li class="menu">                <asp:LinkButton ID="lbMyStats" runat="server">                <asp:Image ID="imMyStats" runat="server" ImageUrl="~/Images/Anonymous_Spreadsheet.png" Height="30" />                <span class="name">My Stats.</span>                <span class="arrow"></span>                </asp:LinkButton>                </li>            <li class="menu">                <asp:LinkButton ID="lbAddAPlace" runat="server" onclick="lbAddAPlace_Click">                <asp:Image ID="imAddAPlace" runat="server" ImageUrl="~/Images/jean_victor_balin_add.png" Height="30" />                <span class="name">Add a Place.</span>                <span class="arrow"></span>                </asp:LinkButton>                </li>            <li class="button">                <input type="button" value="Update Your Current Location" onclick="UpdateLocation_Click()">                </li>        </ul>    </div>    </asp:Panel>    <div>    <asp:Panel ID="pnlCoupons" runat="server" Visible="false">        <div id="topbar">        <div id="title">MapSplore</div>        <div id="leftbutton">            <asp:LinkButton runat="server" Text="Return"                 ID="ReturnFromDeals" OnClick="ReturnFromDeals_Click" /></div></div>    <div class="content">    <asp:ListView ID="lvCoupons" runat="server">        <LayoutTemplate>            <ul class="pageitem" runat="server">                <asp:PlaceHolder ID="itemPlaceholder" runat="server" />            </ul>        </LayoutTemplate>        <ItemTemplate>            <li class="menu">                <asp:LinkButton ID="lbBusiness" runat="server" Text='<%#Eval("Place.Name") %>' OnClick="lbBusiness_Click">                    <span class="comment">                    <asp:Label ID="lblAddress" runat="server" Text='<%#Eval("Place.Address1") %>' />                    <asp:Label ID="lblDis" runat="server" Text='<%# Convert.ToString(Convert.ToInt32(Eval("Place.Distance"))) + " meters" %>' CssClass="smallText" />                    <asp:HiddenField ID="hdPlaceId" runat="server" Value='<%#Eval("PlaceId") %>' />                    <asp:HiddenField ID="hdGeoPromotionId" runat="server" Value='<%#Eval("GeoPromotionId") %>' />                    </span>                    <span class="arrow"></span>                </asp:LinkButton></li></ItemTemplate></asp:ListView><asp:GridView ID="gvCoupons" runat="server" AutoGenerateColumns="false">            <HeaderStyle BackColor="Silver" />            <AlternatingRowStyle BackColor="Wheat" />            <Columns>                <asp:TemplateField AccessibleHeaderText="Business" HeaderText="Business">                    <ItemTemplate>                        <asp:Image ID="imPlaceType" runat="server" Text='<%#Eval("Type") %>' ImageUrl='<%#Eval("Image") %>' />                        <asp:LinkButton ID="lbBusiness" runat="server" Text='<%#Eval("Name") %>' OnClick="lbBusiness_Click" />                        <asp:LinkButton ID="lblAddress" runat="server" Text='<%#Eval("Address1") %>' CssClass="smallText" />                        <asp:Label ID="lblDis" runat="server" Text='<%# Convert.ToString(Convert.ToInt32(Eval("Distance"))) + " meters" %>' CssClass="smallText" />                        <asp:HiddenField ID="hdPlaceId" runat="server" Value='<%#Eval("PlaceId") %>' />                        <asp:HiddenField ID="hdGeoPromotionId" runat="server" Value='<%#Eval("GeoPromotionId") %>' />                        <asp:Label ID="lblInfo" runat="server" Visible="false" />                    </ItemTemplate>                </asp:TemplateField>            </Columns>        </asp:GridView>    </div>    </asp:Panel>    <asp:Panel ID="pnlPlaces" runat="server" Visible="false">    <div id="topbar">        <div id="title">            MapSplore</div><div id="leftbutton">            <asp:LinkButton runat="server" Text="Return"                 ID="ReturnFromPlaces" OnClick="ReturnFromPlaces_Click" /></div></div>        <div id="content">        <asp:ListView ID="lvPlaces" runat="server">            <LayoutTemplate>                <ul id="ulPlaces" class="pageitem" runat="server">                    <asp:PlaceHolder ID="itemPlaceholder" runat="server" />                    <li class="menu">                        <asp:LinkButton ID="lbNotListed" runat="server" CssClass="name"                            OnClick="lbNotListed_Click">                            Place not listed                            <span class="arrow"></span>                            </asp:LinkButton>                    </li>                </ul>            </LayoutTemplate>            <ItemTemplate>            <li class="menu">                <asp:LinkButton ID="lbImHere" runat="server" CssClass="name"                     OnClick="lbImHere_Click">                <%#DisplayName(Eval("Name")) %>&nbsp;                <%# Convert.ToString(Convert.ToInt32(Eval("Distance"))) + " meters" %>                <asp:HiddenField ID="hdPlaceId" runat="server" Value='<%#Eval("PlaceId") %>' />                <span class="arrow"></span>                </asp:LinkButton></li></ItemTemplate></asp:ListView>    </div>    </asp:Panel>    <asp:Panel ID="pnlImHereNow" runat="server" Visible="false">        <div id="topbar">        <div id="title">            MapSplore</div><div id="leftbutton">            <asp:LinkButton runat="server" Text="Places"                 ID="lbImHereNowReturn" OnClick="lbImHereNowReturn_Click" /></div></div>            <div id="rightbutton">            <asp:LinkButton runat="server" Text="Beginning"                ID="lbBackToBeginning" OnClick="lbBackToBeginning_Click" />            </div>        <div id="content">        <ul class="pageitem">        <asp:HiddenField ID="hdPlaceId" runat="server" />        <asp:HiddenField ID="hdPlaceLat" runat="server" />        <asp:HiddenField ID="hdPlaceLon" runat="server" />        <asp:HiddenField ID="hdPlaceTitle" runat="server" />        <asp:Button ID="btnImHereNow" runat="server"             Text="I'm here" OnClick="btnImHereNow_Click" />             <asp:Label ID="lblPlaceTitle" runat="server" /><br />        <asp:TextBox ID="txtWhatsHappening" runat="server" TextMode="MultiLine" Rows="2" style="width:300px" /><br />        <div id="divImHere" style="width:300px; height:300px"></div>        </div>        </ul>    </asp:Panel>    <asp:Panel runat="server" ID="pnlIveBeenHere" Visible="false">        <div id="topbar">        <div id="title">            Where I've been</div><div id="leftbutton">            <asp:LinkButton ID="lbIveBeenHereBack" runat="server" Text="Back" OnClick="lbIveBeenHereBack_Click" /></div></div>        <div id="content">        <asp:ListView ID="lvWhereIveBeen" runat="server">            <LayoutTemplate>                <ul id="ulWhereIveBeen" class="pageitem" runat="server">                    <asp:PlaceHolder ID="itemPlaceholder" runat="server" />                </ul>            </LayoutTemplate>            <ItemTemplate>            <li class="menu" runat="server">                <asp:LinkButton ID="lbPlaceIveBeen" runat="server" OnClick="lbPlaceIveBeen_Click" CssClass="name">                    <asp:Label ID="lblPlace" runat="server" Text='<%#Eval("PlaceName") %>' /> at                    <asp:Label ID="lblTime" runat="server" Text='<%#Eval("ATTime") %>' CssClass="content" />                    <asp:HiddenField ID="hdATID" runat="server" Value='<%#Eval("ATID") %>' />                    <span class="arrow"></span>                </asp:LinkButton>            </li>            </ItemTemplate>        </asp:ListView>        </div>        </asp:Panel>    <asp:Panel runat="server" ID="pnlPlaceIveBeen" Visible="false">        <div id="topbar">        <div id="title">            I've been here        </div>        <div id="leftbutton">            <asp:LinkButton ID="lbPlaceIveBeenBack" runat="server" Text="Back" OnClick="lbPlaceIveBeenBack_Click" />        </div>        <div id="rightbutton">            <asp:LinkButton ID="lbPlaceIveBeenBeginning" runat="server" Text="Beginning" OnClick="lbPlaceIveBeenBeginning_Click" />        </div>        </div>        <div id="content">            <ul class="pageitem">            <li>            <asp:HiddenField ID="hdPlaceIveBeenPlaceId" runat="server" />            <asp:HiddenField ID="hdPlaceIveBeenLatitude" runat="server" />            <asp:HiddenField ID="hdPlaceIveBeenLongitude" runat="server" />            <asp:Label ID="lblPlaceIveBeenName" runat="server" /><br />            <asp:Label ID="lblPlaceIveBeenAddress" runat="server" /><br />            <asp:Label ID="lblPlaceIveBeenCity" runat="server" />,             <asp:Label ID="lblPlaceIveBeenState" runat="server" />            <asp:Label ID="lblPlaceIveBeenZipCode" runat="server" /><br />            <asp:Label ID="lblPlaceIveBeenCountry" runat="server" /><br />            <div id="divPlaceIveBeen" style="width:300px; height:300px"></div>            </li>            </ul>        </div>                </asp:Panel>         <asp:Panel ID="pnlAddPlace" runat="server" Visible="false">                <div id="topbar"><div id="title">MapSplore</div><div id="leftbutton"><asp:LinkButton ID="lbAddPlaceReturn" runat="server" Text="Back" OnClick="lbAddPlaceReturn_Click" /></div><div id="rightnav"></div></div><div id="content">    <ul class="pageitem">        <li id="liPlaceAddMessage" runat="server" visible="false">        <asp:Label ID="PlaceAddMessage" runat="server" />        </li>        <li class="bigfield">        <asp:TextBox ID="txtPlaceName" runat="server" placeholder="Name of Establishment" />        </li>        <li class="bigfield">        <asp:TextBox ID="txtAddress1" runat="server" placeholder="Address 1" />        </li>        <li class="bigfield">        <asp:TextBox ID="txtCity" runat="server" placeholder="City" />        </li>        <li class="select">        <asp:DropDownList ID="ddlProvince" runat="server" placeholder="Select State" />          <span class="arrow"></span>              </li>        <li class="bigfield">        <asp:TextBox ID="txtZipCode" runat="server" placeholder="Zip Code" />        </li>        <li class="select">        <asp:DropDownList ID="ddlCountry" runat="server"             onselectedindexchanged="ddlCountry_SelectedIndexChanged" />        <span class="arrow"></span>        </li>        <li class="bigfield">        <asp:TextBox ID="txtPhoneNumber" runat="server" placeholder="Phone Number" />        </li>        <li class="checkbox">            <span class="name">You Here Now:</span> <asp:CheckBox ID="cbYouHereNow" runat="server" Checked="true" />        </li>        <li class="button">        <asp:Button ID="btnAdd" runat="server" Text="Add Place"             onclick="btnAdd_Click" />        </li>    </ul></div>        </asp:Panel>        <asp:Panel ID="pnlImHere" runat="server" Visible="false">            <asp:TextBox ID="txtImHere" runat="server"                 TextMode="MultiLine" Rows="3" Columns="40" /><br />            <asp:DropDownList ID="ddlPlace" runat="server" /><br />            <asp:Button ID="btnHere" runat="server" Text="Tell Everyone I'm Here"                 onclick="btnHere_Click" /><br />        </asp:Panel>     </div>    </ContentTemplate>    </asp:UpdatePanel> </asp:Content> Code Behind .cs file: using System;using System.Collections.Generic;using System.Linq;using System.Web;using System.Web.Security;using System.Web.UI;using System.Web.UI.HtmlControls;using System.Web.UI.WebControls;using LocationDataModel; public partial class AT_iPhone_Default : ViewStatePage{    private iPhoneDevice ipd;     protected void Page_Load(object sender, EventArgs e)    {        LocationDataEntities lde = new LocationDataEntities();        if (!Page.IsPostBack)        {            var Countries = from c in lde.Countries select c;            foreach (Country co in Countries)            {                ddlCountry.Items.Add(new ListItem(co.Name, co.CountryId.ToString()));            }            ddlCountry_SelectedIndexChanged(ddlCountry, null);            if (AppleIPhone.IsIPad())                ipd = iPhoneDevice.iPad;            if (AppleIPhone.IsIPhone())                ipd = iPhoneDevice.iPhone;            if (AppleIPhone.IsIPodTouch())                ipd = iPhoneDevice.iPodTouch;        }    }    protected void btnPlaces_Click(object sender, EventArgs e)    {    }    protected void btnAdd_Click(object sender, EventArgs e)    {        bool blImHere = cbYouHereNow.Checked;        string Place = txtPlaceName.Text,            Address1 = txtAddress1.Text,            City = txtCity.Text,            ZipCode = txtZipCode.Text,            PhoneNumber = txtPhoneNumber.Text,            ProvinceId = ddlProvince.SelectedItem.Value,            CountryId = ddlCountry.SelectedItem.Value;        int iProvinceId, iCountryId;        double dLatitude, dLongitude;        DataAccess da = new DataAccess();        if ((!String.IsNullOrEmpty(ProvinceId)) &&            (!String.IsNullOrEmpty(CountryId)))        {            iProvinceId = Convert.ToInt32(ProvinceId);            iCountryId = Convert.ToInt32(CountryId);            if (blImHere)            {                dLatitude = Convert.ToDouble(Latitude.Value);                dLongitude = Convert.ToDouble(Longitude.Value);                da.StorePlace(Place, Address1, String.Empty, City,                    iProvinceId, ZipCode, iCountryId, PhoneNumber,                    dLatitude, dLongitude);            }            else            {                da.StorePlace(Place, Address1, String.Empty, City,                    iProvinceId, ZipCode, iCountryId, PhoneNumber);            }            liPlaceAddMessage.Visible = true;            PlaceAddMessage.Text = "Awesome, your place has been added. Add Another!";            txtPlaceName.Text = String.Empty;            txtAddress1.Text = String.Empty;            txtCity.Text = String.Empty;            ddlProvince.SelectedIndex = -1;            txtZipCode.Text = String.Empty;            txtPhoneNumber.Text = String.Empty;        }        else        {            liPlaceAddMessage.Visible = true;            PlaceAddMessage.Text = "Please select a State and a Country.";        }    }    protected void ddlCountry_SelectedIndexChanged(object sender, EventArgs e)    {        string CountryId = ddlCountry.SelectedItem.Value;        if (!String.IsNullOrEmpty(CountryId))        {            int iCountryId = Convert.ToInt32(CountryId);            LocationDataModel.LocationDataEntities lde = new LocationDataModel.LocationDataEntities();            var prov = from p in lde.Provinces where p.CountryId == iCountryId                        orderby p.ProvinceName select p;                        ddlProvince.Items.Add(String.Empty);            foreach (Province pr in prov)            {                ddlProvince.Items.Add(new ListItem(pr.ProvinceName, pr.ProvinceId.ToString()));            }        }        else        {            ddlProvince.Items.Clear();        }    }    protected void btnImHere_Click(object sender, EventArgs e)    {        int i = 0;        DataAccess da = new DataAccess();        double Lat = Convert.ToDouble(Latitude.Value),            Lon = Convert.ToDouble(Longitude.Value);        List<Place> lp = da.NearByLocations(Lat, Lon);        foreach (Place p in lp)        {            ListItem li = new ListItem(p.Name, p.PlaceId.ToString());            if (i == 0)            {                li.Selected = true;            }            ddlPlace.Items.Add(li);            i++;        }        pnlAddPlace.Visible = false;        pnlImHere.Visible = true;    }    protected void lbImHere_Click(object sender, EventArgs e)    {        string UserName = Membership.GetUser().UserName;        ListViewItem lvi = (ListViewItem)(((LinkButton)sender).Parent);        HiddenField hd = (HiddenField)lvi.FindControl("hdPlaceId");        long PlaceId = Convert.ToInt64(hd.Value);        double dLatitude = Convert.ToDouble(Latitude.Value);        double dLongitude = Convert.ToDouble(Longitude.Value);        DataAccess da = new DataAccess();        Place pl = da.GetPlace(PlaceId);        pnlImHereNow.Visible = true;        pnlPlaces.Visible = false;        hdPlaceId.Value = PlaceId.ToString();        hdPlaceLat.Value = pl.Latitude.ToString();        hdPlaceLon.Value = pl.Longitude.ToString();        hdPlaceTitle.Value = pl.Name;        lblPlaceTitle.Text = pl.Name;    }    protected void btnHere_Click(object sender, EventArgs e)    {        string UserName = Membership.GetUser().UserName;        string WhatsH = txtImHere.Text;        long PlaceId = Convert.ToInt64(ddlPlace.SelectedValue);        double dLatitude = Convert.ToDouble(Latitude.Value);        double dLongitude = Convert.ToDouble(Longitude.Value);        DataAccess da = new DataAccess();        da.StoreUserAT(UserName, PlaceId, WhatsH,            dLatitude, dLongitude);    }    protected void btnLocalCoupons_Click(object sender, EventArgs e)    {        double dLatitude = Convert.ToDouble(Latitude.Value);        double dLongitude = Convert.ToDouble(Longitude.Value);        DataAccess da = new DataAccess();     }    protected void lbBusiness_Click(object sender, EventArgs e)    {        string UserName = Membership.GetUser().UserName;        GridViewRow gvr = (GridViewRow)(((LinkButton)sender).Parent.Parent);        HiddenField hd = (HiddenField)gvr.FindControl("hdPlaceId");        string sPlaceId = hd.Value;        Int64 PlaceId;        if (!String.IsNullOrEmpty(sPlaceId))        {            PlaceId = Convert.ToInt64(sPlaceId);        }    }    protected void lbLocalDeals_Click(object sender, EventArgs e)    {        double dLatitude = Convert.ToDouble(Latitude.Value);        double dLongitude = Convert.ToDouble(Longitude.Value);        DataAccess da = new DataAccess();        pnlCoupons.Visible = true;        pnlStart.Visible = false;        List<GeoPromotion> lgp = da.NearByDeals(dLatitude, dLongitude);        lvCoupons.DataSource = lgp;        lvCoupons.DataBind();    }    protected void lbLocalPlaces_Click(object sender, EventArgs e)    {        DataAccess da = new DataAccess();        double Lat = Convert.ToDouble(Latitude.Value);        double Lon = Convert.ToDouble(Longitude.Value);        List<LocationDataModel.Place> places = da.NearByLocations(Lat, Lon);        lvPlaces.DataSource = places;        lvPlaces.SelectedIndex = -1;        lvPlaces.DataBind();        pnlPlaces.Visible = true;        pnlStart.Visible = false;    }    protected void ReturnFromPlaces_Click(object sender, EventArgs e)    {        pnlPlaces.Visible = false;        pnlStart.Visible = true;    }    protected void ReturnFromDeals_Click(object sender, EventArgs e)    {        pnlCoupons.Visible = false;        pnlStart.Visible = true;    }    protected void btnImHereNow_Click(object sender, EventArgs e)    {        long PlaceId = Convert.ToInt32(hdPlaceId.Value);        string UserName = Membership.GetUser().UserName;        string WhatsHappening = txtWhatsHappening.Text;        double UserLat = Convert.ToDouble(Latitude.Value);        double UserLon = Convert.ToDouble(Longitude.Value);        DataAccess da = new DataAccess();        da.StoreUserAT(UserName, PlaceId, WhatsHappening,             UserLat, UserLon);    }    protected void lbImHereNowReturn_Click(object sender, EventArgs e)    {        pnlImHereNow.Visible = false;        pnlPlaces.Visible = true;    }    protected void lbBackToBeginning_Click(object sender, EventArgs e)    {        pnlStart.Visible = true;        pnlImHereNow.Visible = false;    }    protected void lbWhereIveBeen_Click(object sender, EventArgs e)    {        string UserName = Membership.GetUser().UserName;        pnlStart.Visible = false;        pnlIveBeenHere.Visible = true;        DataAccess da = new DataAccess();        lvWhereIveBeen.DataSource = da.UserATs(UserName, 0, 15);        lvWhereIveBeen.DataBind();    }    protected void lbIveBeenHereBack_Click(object sender, EventArgs e)    {        pnlIveBeenHere.Visible = false;        pnlStart.Visible = true;    }     protected void lbPlaceIveBeen_Click(object sender, EventArgs e)    {        LinkButton lb = (LinkButton)sender;        ListViewItem lvi = (ListViewItem)lb.Parent.Parent;        HiddenField hdATID = (HiddenField)lvi.FindControl("hdATID");        Int64 ATID = Convert.ToInt64(hdATID.Value);        DataAccess da = new DataAccess();        pnlIveBeenHere.Visible = false;        pnlPlaceIveBeen.Visible = true;        var plac = da.GetPlaceViaATID(ATID);        hdPlaceIveBeenPlaceId.Value = plac.PlaceId.ToString();        hdPlaceIveBeenLatitude.Value = plac.Latitude.ToString();        hdPlaceIveBeenLongitude.Value = plac.Longitude.ToString();        lblPlaceIveBeenName.Text = plac.Name;        lblPlaceIveBeenAddress.Text = plac.Address1;        lblPlaceIveBeenCity.Text = plac.City;        lblPlaceIveBeenState.Text = plac.Province.ProvinceName;        lblPlaceIveBeenZipCode.Text = plac.ZipCode;        lblPlaceIveBeenCountry.Text = plac.Country.Name;    }     protected void lbNotListed_Click(object sender, EventArgs e)    {        SetupAddPoint();        pnlPlaces.Visible = false;    }     protected void lbAddAPlace_Click(object sender, EventArgs e)    {        SetupAddPoint();    }     private void SetupAddPoint()    {        double lat = Convert.ToDouble(Latitude.Value);        double lon = Convert.ToDouble(Longitude.Value);        DataAccess da = new DataAccess();        var zip = da.WhereAmIAt(lat, lon);        if (zip.Count > 0)        {            var z0 = zip[0];            txtCity.Text = z0.City;            txtZipCode.Text = z0.ZipCode;            ddlProvince.ClearSelection();            if (z0.ProvinceId.HasValue == true)            {                foreach (ListItem li in ddlProvince.Items)                {                    if (li.Value == z0.ProvinceId.Value.ToString())                    {                        li.Selected = true;                        break;                    }                }            }        }        pnlAddPlace.Visible = true;        pnlStart.Visible = false;    }    protected void lbAddPlaceReturn_Click(object sender, EventArgs e)    {        pnlAddPlace.Visible = false;        pnlStart.Visible = true;        liPlaceAddMessage.Visible = false;        PlaceAddMessage.Text = String.Empty;    }    protected void lbPlaceIveBeenBack_Click(object sender, EventArgs e)    {        pnlIveBeenHere.Visible = true;        pnlPlaceIveBeen.Visible = false;            }    protected void lbPlaceIveBeenBeginning_Click(object sender, EventArgs e)    {        pnlPlaceIveBeen.Visible = false;        pnlStart.Visible = true;    }    protected string DisplayName(object val)    {        string strVal = Convert.ToString(val);         if (AppleIPhone.IsIPad())        {            ipd = iPhoneDevice.iPad;        }        if (AppleIPhone.IsIPhone())        {            ipd = iPhoneDevice.iPhone;        }        if (AppleIPhone.IsIPodTouch())        {            ipd = iPhoneDevice.iPodTouch;        }        return (iPhoneHelper.DisplayContentOnMenu(strVal, ipd));    }} iPhoneHelper.cs file: using System;using System.Collections.Generic;using System.Linq;using System.Web; public enum iPhoneDevice{    iPhone, iPodTouch, iPad}/// <summary>/// Summary description for iPhoneHelper/// </summary>/// public class iPhoneHelper{ public iPhoneHelper() {  //  // TODO: Add constructor logic here  // } // This code is stupid in retrospect. Use css to solve this problem      public static string DisplayContentOnMenu(string val, iPhoneDevice ipd)    {        string Return = val;        string Elipsis = "...";        int iPadMaxLength = 30;        int iPhoneMaxLength = 15;        if (ipd == iPhoneDevice.iPad)        {            if (Return.Length > iPadMaxLength)            {                Return = Return.Substring(0, iPadMaxLength - Elipsis.Length) + Elipsis;            }        }        else        {            if (Return.Length > iPhoneMaxLength)            {                Return = Return.Substring(0, iPhoneMaxLength - Elipsis.Length) + Elipsis;            }        }        return (Return);    }}  Source code for the ViewStatePage: using System;using System.Data;using System.Data.SqlClient;using System.Configuration;using System.Web;using System.Web.Security;using System.Web.UI;using System.Web.UI.WebControls;using System.Web.UI.WebControls.WebParts;using System.Web.UI.HtmlControls; /// <summary>/// Summary description for BasePage/// </summary>#region Base class for a page.public class ViewStatePage : System.Web.UI.Page{     PageStatePersisterToDatabase myPageStatePersister;        public ViewStatePage()        : base()    {        myPageStatePersister = new PageStatePersisterToDatabase(this);    }     protected override PageStatePersister PageStatePersister    {        get        {            return myPageStatePersister;        }    } }#endregion #region This class will override the page persistence to store page state in a database.public class PageStatePersisterToDatabase : PageStatePersister{    private string ViewStateKeyField = "__VIEWSTATE_KEY";    private string _exNoConnectionStringFound = "No Database Configuration information is in the web.config.";     public PageStatePersisterToDatabase(Page page)        : base(page)    {    }     public override void Load()    {         // Get the cache key from the web form data        System.Int64 key = Convert.ToInt64(Page.Request.Params[ViewStateKeyField]);         Pair state = this.LoadState(key);         // Abort if cache object is not of type Pair        if (state == null)            throw new ApplicationException("Missing valid " + ViewStateKeyField);         // Set view state and control state        ViewState = state.First;        ControlState = state.Second;    }     public override void Save()    {         // No processing needed if no states available        if (ViewState == null && ControlState != null)            return;         System.Int64 key;        IStateFormatter formatter = this.StateFormatter;        Pair statePair = new Pair(ViewState, ControlState);         // Serialize the statePair object to a string.        string serializedState = formatter.Serialize(statePair);         // Save the ViewState and get a unique identifier back.        key = SaveState(serializedState);         // Register hidden field to store cache key in        // Page.ClientScript does not work properly with Atlas.        //Page.ClientScript.RegisterHiddenField(ViewStateKeyField, key.ToString());        ScriptManager.RegisterHiddenField(this.Page, ViewStateKeyField, key.ToString());    }     private System.Int64 SaveState(string PageState)    {        System.Int64 i64Key = 0;        string strConn = String.Empty,            strProvider = String.Empty;         string strSql = "insert into tblPageState ( SerializedState ) values ( '" + SqlEscape(PageState) + "');select scope_identity();";        SqlConnection sqlCn;        SqlCommand sqlCm;        try        {            GetDBConnectionString(ref strConn, ref strProvider);            sqlCn = new SqlConnection(strConn);            sqlCm = new SqlCommand(strSql, sqlCn);            sqlCn.Open();            i64Key = Convert.ToInt64(sqlCm.ExecuteScalar());            if (sqlCn.State != ConnectionState.Closed)            {                sqlCn.Close();            }            sqlCn.Dispose();            sqlCm.Dispose();        }        finally        {            sqlCn = null;            sqlCm = null;        }        return i64Key;    }     private Pair LoadState(System.Int64 iKey)    {        string strConn = String.Empty,            strProvider = String.Empty,            SerializedState = String.Empty,            strMinutesInPast = GetMinutesInPastToDelete();        Pair PageState;        string strSql = "select SerializedState from tblPageState where tblPageStateID=" + iKey.ToString() + ";" +            "delete from tblPageState where DateUpdated<DateAdd(mi, " + strMinutesInPast + ", getdate());";        SqlConnection sqlCn;        SqlCommand sqlCm;        try        {            GetDBConnectionString(ref strConn, ref strProvider);            sqlCn = new SqlConnection(strConn);            sqlCm = new SqlCommand(strSql, sqlCn);             sqlCn.Open();            SerializedState = Convert.ToString(sqlCm.ExecuteScalar());            IStateFormatter formatter = this.StateFormatter;             if ((null == SerializedState) ||                (String.Empty == SerializedState))            {                throw (new ApplicationException("No ViewState records were returned."));            }             // Deserilize returns the Pair object that is serialized in            // the Save method.            PageState = (Pair)formatter.Deserialize(SerializedState);             if (sqlCn.State != ConnectionState.Closed)            {                sqlCn.Close();            }            sqlCn.Dispose();            sqlCm.Dispose();        }        finally        {            sqlCn = null;            sqlCm = null;        }        return PageState;    }     private string SqlEscape(string Val)    {        string ReturnVal = String.Empty;        if (null != Val)        {            ReturnVal = Val.Replace("'", "''");        }        return (ReturnVal);    }    private void GetDBConnectionString(ref string ConnectionStringValue, ref string ProviderNameValue)    {        if (System.Configuration.ConfigurationManager.ConnectionStrings.Count > 0)        {            ConnectionStringValue = System.Configuration.ConfigurationManager.ConnectionStrings["ApplicationServices"].ConnectionString;            ProviderNameValue = System.Configuration.ConfigurationManager.ConnectionStrings["ApplicationServices"].ProviderName;        }        else        {            throw new ConfigurationErrorsException(_exNoConnectionStringFound);        }    }    private string GetMinutesInPastToDelete()    {        string strReturn = "-60";        if (null != System.Configuration.ConfigurationManager.AppSettings["MinutesInPastToDeletePageState"])        {            strReturn = System.Configuration.ConfigurationManager.AppSettings["MinutesInPastToDeletePageState"].ToString();        }        return (strReturn);    }}#endregion AppleiPhone.cs file: using System;using System.Collections.Generic;using System.Linq;using System.Web; /// <summary>/// Summary description for AppleIPhone/// </summary>public class AppleIPhone{ public AppleIPhone() {  //  // TODO: Add constructor logic here  // }     static public bool IsIPhoneOS()    {        return (IsIPad() || IsIPhone() || IsIPodTouch());    }     static public bool IsIPhone()    {        return IsTest("iPhone");    }     static public bool IsIPodTouch()    {        return IsTest("iPod");    }     static public bool IsIPad()    {        return IsTest("iPad");    }     static private bool IsTest(string Agent)    {        bool bl = false;        string ua = HttpContext.Current.Request.UserAgent.ToLower();        try        {            bl = ua.Contains(Agent.ToLower());        }        catch { }        return (bl);        }} Master page .cs: using System;using System.Collections.Generic;using System.Linq;using System.Web;using System.Web.UI;using System.Web.UI.HtmlControls;using System.Web.UI.WebControls; public partial class MasterPages_iPhoneMaster : System.Web.UI.MasterPage{    protected void Page_Load(object sender, EventArgs e)    {            HtmlHead head = Page.Header;            HtmlMeta meta = new HtmlMeta();            if (AppleIPhone.IsIPad() == true)            {                meta.Content = "width=400,user-scalable=no";                head.Controls.Add(meta);             }            else            {                meta.Content = "width=device-width, user-scalable=no";                meta.Attributes.Add("name", "viewport");            }            meta.Attributes.Add("name", "viewport");            head.Controls.Add(meta);            HtmlLink cssLink = new HtmlLink();            HtmlGenericControl script = new HtmlGenericControl("script");            script.Attributes.Add("type", "text/javascript");            script.Attributes.Add("src", ResolveUrl("~/Scripts/iWebKit/javascript/functions.js"));            head.Controls.Add(script);            cssLink.Attributes.Add("rel", "stylesheet");            cssLink.Attributes.Add("href", ResolveUrl("~/Scripts/iWebKit/css/style.css") );            cssLink.Attributes.Add("type", "text/css");            head.Controls.Add(cssLink);            HtmlGenericControl jsLink = new HtmlGenericControl("script");            //jsLink.Attributes.Add("type", "text/javascript");            //jsLink.Attributes.Add("src", ResolveUrl("~/Scripts/jquery-1.4.1.min.js") );            //head.Controls.Add(jsLink);            HtmlLink appleIcon = new HtmlLink();            appleIcon.Attributes.Add("rel", "apple-touch-icon");            appleIcon.Attributes.Add("href", ResolveUrl("~/apple-touch-icon.png"));            HtmlMeta appleMobileWebAppStatusBarStyle = new HtmlMeta();            appleMobileWebAppStatusBarStyle.Attributes.Add("name", "apple-mobile-web-app-status-bar-style");            appleMobileWebAppStatusBarStyle.Attributes.Add("content", "black");            head.Controls.Add(appleMobileWebAppStatusBarStyle);    }     internal string FindPath(string Location)    {        string Url = Server.MapPath(Location);        return (Url);    }}

    Read the article

  • C#/.NET Little Wonders: ConcurrentBag and BlockingCollection

    - by James Michael Hare
    In the first week of concurrent collections, began with a general introduction and discussed the ConcurrentStack<T> and ConcurrentQueue<T>.  The last post discussed the ConcurrentDictionary<T> .  Finally this week, we shall close with a discussion of the ConcurrentBag<T> and BlockingCollection<T>. For more of the "Little Wonders" posts, see C#/.NET Little Wonders: A Redux. Recap As you'll recall from the previous posts, the original collections were object-based containers that accomplished synchronization through a Synchronized member.  With the advent of .NET 2.0, the original collections were succeeded by the generic collections which are fully type-safe, but eschew automatic synchronization.  With .NET 4.0, a new breed of collections was born in the System.Collections.Concurrent namespace.  Of these, the final concurrent collection we will examine is the ConcurrentBag and a very useful wrapper class called the BlockingCollection. For some excellent information on the performance of the concurrent collections and how they perform compared to a traditional brute-force locking strategy, see this informative whitepaper by the Microsoft Parallel Computing Platform team here. ConcurrentBag<T> – Thread-safe unordered collection. Unlike the other concurrent collections, the ConcurrentBag<T> has no non-concurrent counterpart in the .NET collections libraries.  Items can be added and removed from a bag just like any other collection, but unlike the other collections, the items are not maintained in any order.  This makes the bag handy for those cases when all you care about is that the data be consumed eventually, without regard for order of consumption or even fairness – that is, it’s possible new items could be consumed before older items given the right circumstances for a period of time. So why would you ever want a container that can be unfair?  Well, to look at it another way, you can use a ConcurrentQueue and get the fairness, but it comes at a cost in that the ordering rules and synchronization required to maintain that ordering can affect scalability a bit.  Thus sometimes the bag is great when you want the fastest way to get the next item to process, and don’t care what item it is or how long its been waiting. The way that the ConcurrentBag works is to take advantage of the new ThreadLocal<T> type (new in System.Threading for .NET 4.0) so that each thread using the bag has a list local to just that thread.  This means that adding or removing to a thread-local list requires very low synchronization.  The problem comes in where a thread goes to consume an item but it’s local list is empty.  In this case the bag performs “work-stealing” where it will rob an item from another thread that has items in its list.  This requires a higher level of synchronization which adds a bit of overhead to the take operation. So, as you can imagine, this makes the ConcurrentBag good for situations where each thread both produces and consumes items from the bag, but it would be less-than-idea in situations where some threads are dedicated producers and the other threads are dedicated consumers because the work-stealing synchronization would outweigh the thread-local optimization for a thread taking its own items. Like the other concurrent collections, there are some curiosities to keep in mind: IsEmpty(), Count, ToArray(), and GetEnumerator() lock collection Each of these needs to take a snapshot of whole bag to determine if empty, thus they tend to be more expensive and cause Add() and Take() operations to block. ToArray() and GetEnumerator() are static snapshots Because it is based on a snapshot, will not show subsequent updates after snapshot. Add() is lightweight Since adding to the thread-local list, there is very little overhead on Add. TryTake() is lightweight if items in thread-local list As long as items are in the thread-local list, TryTake() is very lightweight, much more so than ConcurrentStack() and ConcurrentQueue(), however if the local thread list is empty, it must steal work from another thread, which is more expensive. Remember, a bag is not ideal for all situations, it is mainly ideal for situations where a process consumes an item and either decomposes it into more items to be processed, or handles the item partially and places it back to be processed again until some point when it will complete.  The main point is that the bag works best when each thread both takes and adds items. For example, we could create a totally contrived example where perhaps we want to see the largest power of a number before it crosses a certain threshold.  Yes, obviously we could easily do this with a log function, but bare with me while I use this contrived example for simplicity. So let’s say we have a work function that will take a Tuple out of a bag, this Tuple will contain two ints.  The first int is the original number, and the second int is the last multiple of that number.  So we could load our bag with the initial values (let’s say we want to know the last multiple of each of 2, 3, 5, and 7 under 100. 1: var bag = new ConcurrentBag<Tuple<int, int>> 2: { 3: Tuple.Create(2, 1), 4: Tuple.Create(3, 1), 5: Tuple.Create(5, 1), 6: Tuple.Create(7, 1) 7: }; Then we can create a method that given the bag, will take out an item, apply the multiplier again, 1: public static void FindHighestPowerUnder(ConcurrentBag<Tuple<int,int>> bag, int threshold) 2: { 3: Tuple<int,int> pair; 4:  5: // while there are items to take, this will prefer local first, then steal if no local 6: while (bag.TryTake(out pair)) 7: { 8: // look at next power 9: var result = Math.Pow(pair.Item1, pair.Item2 + 1); 10:  11: if (result < threshold) 12: { 13: // if smaller than threshold bump power by 1 14: bag.Add(Tuple.Create(pair.Item1, pair.Item2 + 1)); 15: } 16: else 17: { 18: // otherwise, we're done 19: Console.WriteLine("Highest power of {0} under {3} is {0}^{1} = {2}.", 20: pair.Item1, pair.Item2, Math.Pow(pair.Item1, pair.Item2), threshold); 21: } 22: } 23: } Now that we have this, we can load up this method as an Action into our Tasks and run it: 1: // create array of tasks, start all, wait for all 2: var tasks = new[] 3: { 4: new Task(() => FindHighestPowerUnder(bag, 100)), 5: new Task(() => FindHighestPowerUnder(bag, 100)), 6: }; 7:  8: Array.ForEach(tasks, t => t.Start()); 9:  10: Task.WaitAll(tasks); Totally contrived, I know, but keep in mind the main point!  When you have a thread or task that operates on an item, and then puts it back for further consumption – or decomposes an item into further sub-items to be processed – you should consider a ConcurrentBag as the thread-local lists will allow for quick processing.  However, if you need ordering or if your processes are dedicated producers or consumers, this collection is not ideal.  As with anything, you should performance test as your mileage will vary depending on your situation! BlockingCollection<T> – A producers & consumers pattern collection The BlockingCollection<T> can be treated like a collection in its own right, but in reality it adds a producers and consumers paradigm to any collection that implements the interface IProducerConsumerCollection<T>.  If you don’t specify one at the time of construction, it will use a ConcurrentQueue<T> as its underlying store. If you don’t want to use the ConcurrentQueue, the ConcurrentStack and ConcurrentBag also implement the interface (though ConcurrentDictionary does not).  In addition, you are of course free to create your own implementation of the interface. So, for those who don’t remember the producers and consumers classical computer-science problem, the gist of it is that you have one (or more) processes that are creating items (producers) and one (or more) processes that are consuming these items (consumers).  Now, the crux of the problem is that there is a bin (queue) where the produced items are placed, and typically that bin has a limited size.  Thus if a producer creates an item, but there is no space to store it, it must wait until an item is consumed.  Also if a consumer goes to consume an item and none exists, it must wait until an item is produced. The BlockingCollection makes it trivial to implement any standard producers/consumers process set by providing that “bin” where the items can be produced into and consumed from with the appropriate blocking operations.  In addition, you can specify whether the bin should have a limited size or can be (theoretically) unbounded, and you can specify timeouts on the blocking operations. As far as your choice of “bin”, for the most part the ConcurrentQueue is the right choice because it is fairly light and maximizes fairness by ordering items so that they are consumed in the same order they are produced.  You can use the concurrent bag or stack, of course, but your ordering would be random-ish in the case of the former and LIFO in the case of the latter. So let’s look at some of the methods of note in BlockingCollection: BoundedCapacity returns capacity of the “bin” If the bin is unbounded, the capacity is int.MaxValue. Count returns an internally-kept count of items This makes it O(1), but if you modify underlying collection directly (not recommended) it is unreliable. CompleteAdding() is used to cut off further adds. This sets IsAddingCompleted and begins to wind down consumers once empty. IsAddingCompleted is true when producers are “done”. Once you are done producing, should complete the add process to alert consumers. IsCompleted is true when producers are “done” and “bin” is empty. Once you mark the producers done, and all items removed, this will be true. Add() is a blocking add to collection. If bin is full, will wait till space frees up Take() is a blocking remove from collection. If bin is empty, will wait until item is produced or adding is completed. GetConsumingEnumerable() is used to iterate and consume items. Unlike the standard enumerator, this one consumes the items instead of iteration. TryAdd() attempts add but does not block completely If adding would block, returns false instead, can specify TimeSpan to wait before stopping. TryTake() attempts to take but does not block completely Like TryAdd(), if taking would block, returns false instead, can specify TimeSpan to wait. Note the use of CompleteAdding() to signal the BlockingCollection that nothing else should be added.  This means that any attempts to TryAdd() or Add() after marked completed will throw an InvalidOperationException.  In addition, once adding is complete you can still continue to TryTake() and Take() until the bin is empty, and then Take() will throw the InvalidOperationException and TryTake() will return false. So let’s create a simple program to try this out.  Let’s say that you have one process that will be producing items, but a slower consumer process that handles them.  This gives us a chance to peek inside what happens when the bin is bounded (by default, the bin is NOT bounded). 1: var bin = new BlockingCollection<int>(5); Now, we create a method to produce items: 1: public static void ProduceItems(BlockingCollection<int> bin, int numToProduce) 2: { 3: for (int i = 0; i < numToProduce; i++) 4: { 5: // try for 10 ms to add an item 6: while (!bin.TryAdd(i, TimeSpan.FromMilliseconds(10))) 7: { 8: Console.WriteLine("Bin is full, retrying..."); 9: } 10: } 11:  12: // once done producing, call CompleteAdding() 13: Console.WriteLine("Adding is completed."); 14: bin.CompleteAdding(); 15: } And one to consume them: 1: public static void ConsumeItems(BlockingCollection<int> bin) 2: { 3: // This will only be true if CompleteAdding() was called AND the bin is empty. 4: while (!bin.IsCompleted) 5: { 6: int item; 7:  8: if (!bin.TryTake(out item, TimeSpan.FromMilliseconds(10))) 9: { 10: Console.WriteLine("Bin is empty, retrying..."); 11: } 12: else 13: { 14: Console.WriteLine("Consuming item {0}.", item); 15: Thread.Sleep(TimeSpan.FromMilliseconds(20)); 16: } 17: } 18: } Then we can fire them off: 1: // create one producer and two consumers 2: var tasks = new[] 3: { 4: new Task(() => ProduceItems(bin, 20)), 5: new Task(() => ConsumeItems(bin)), 6: new Task(() => ConsumeItems(bin)), 7: }; 8:  9: Array.ForEach(tasks, t => t.Start()); 10:  11: Task.WaitAll(tasks); Notice that the producer is faster than the consumer, thus it should be hitting a full bin often and displaying the message after it times out on TryAdd(). 1: Consuming item 0. 2: Consuming item 1. 3: Bin is full, retrying... 4: Bin is full, retrying... 5: Consuming item 3. 6: Consuming item 2. 7: Bin is full, retrying... 8: Consuming item 4. 9: Consuming item 5. 10: Bin is full, retrying... 11: Consuming item 6. 12: Consuming item 7. 13: Bin is full, retrying... 14: Consuming item 8. 15: Consuming item 9. 16: Bin is full, retrying... 17: Consuming item 10. 18: Consuming item 11. 19: Bin is full, retrying... 20: Consuming item 12. 21: Consuming item 13. 22: Bin is full, retrying... 23: Bin is full, retrying... 24: Consuming item 14. 25: Adding is completed. 26: Consuming item 15. 27: Consuming item 16. 28: Consuming item 17. 29: Consuming item 19. 30: Consuming item 18. Also notice that once CompleteAdding() is called and the bin is empty, the IsCompleted property returns true, and the consumers will exit. Summary The ConcurrentBag is an interesting collection that can be used to optimize concurrency scenarios where tasks or threads both produce and consume items.  In this way, it will choose to consume its own work if available, and then steal if not.  However, in situations where you want fair consumption or ordering, or in situations where the producers and consumers are distinct processes, the bag is not optimal. The BlockingCollection is a great wrapper around all of the concurrent queue, stack, and bag that allows you to add producer and consumer semantics easily including waiting when the bin is full or empty. That’s the end of my dive into the concurrent collections.  I’d also strongly recommend, once again, you read this excellent Microsoft white paper that goes into much greater detail on the efficiencies you can gain using these collections judiciously (here). Tweet Technorati Tags: C#,.NET,Concurrent Collections,Little Wonders

    Read the article

  • Does hiding images on 404 error affect SEO?

    - by Question Overflow
    I have a dynamic website that allows registered users to upload and display images on the their profile page. As each user may upload less than the maximum limit of 20 images, there would be some "empty" images on the page. I am using javascript to hide these empty images. The loading of the profile page would generate a series of 404 errors depending on the number of empty images. Would these 404 errors affect the SEO of the page and the website?

    Read the article

  • Questions about game states

    - by MrPlow
    I'm trying to make a framework for a game I've wanted to do for quite a while. The first thing that I decided to implement was a state system for game states. When my "original" idea of having a doubly linked list of game states failed I found This blog and liked the idea of a stack based game state manager. However there were a few things I found weird: Instead of RAII two class methods are used to initialize and destroy the state Every game state class is a singleton(and singletons are bad aren't they?) Every GameState object is static So I took the idea and altered a few things and got this: GameState.h class GameState { private: bool m_paused; protected: StateManager& m_manager; public: GameState(StateManager& manager) : m_manager(manager), m_paused(false){} virtual ~GameState() {} virtual void update() = 0; virtual void draw() = 0; virtual void handleEvents() = 0; void pause() { m_paused = true; } void resume() { m_paused = false; } void changeState(std::unique_ptr<GameState> state) { m_manager.changeState(std::move(state)); } }; StateManager.h class GameState; class StateManager { private: std::vector< std::unique_ptr<GameState> > m_gameStates; public: StateManager(); void changeState(std::unique_ptr<GameState> state); void StateManager::pushState(std::unique_ptr<GameState> state); void popState(); void update(); void draw(); void handleEvents(); }; StateManager.cpp StateManager::StateManager() {} void StateManager::changeState( std::unique_ptr<GameState> state ) { if(!m_gameStates.empty()) { m_gameStates.pop_back(); } m_gameStates.push_back( std::move(state) ); } void StateManager::pushState(std::unique_ptr<GameState> state) { if(!m_gameStates.empty()) { m_gameStates.back()->pause(); } m_gameStates.push_back( std::move(state) ); } void StateManager::popState() { if(!m_gameStates.empty()) m_gameStates.pop_back(); } void StateManager::update() { if(!m_gameStates.empty()) m_gameStates.back()->update(); } void StateManager::draw() { if(!m_gameStates.empty()) m_gameStates.back()->draw(); } void StateManager::handleEvents() { if(!m_gameStates.empty()) m_gameStates.back()->handleEvents(); } And it's used like this: main.cpp StateManager states; states.changeState( std::unique_ptr<GameState>(new GameStateIntro(states)) ); while(gamewindow::gameWindow.isOpen()) { states.handleEvents(); states.update(); states.draw(); } Constructors/Destructors are used to create/destroy states instead of specialized class methods, state objects are no longer static but

    Read the article

< Previous Page | 35 36 37 38 39 40 41 42 43 44 45 46  | Next Page >