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• Scale transform in xaml (in a controltemplate) on a button to perform a "zoom"

  - by Matt B

  Hi all, I've got a button with an image in it and it's being styled by the following: <ControlTemplate x:Key="IconButton" TargetType="Button"> <Border> <ContentPresenter Height="80" Width="80" /> </Border> <ControlTemplate.Triggers> <EventTrigger RoutedEvent="Button.Click"> <BeginStoryboard> <Storyboard TargetProperty="Opacity"> <DoubleAnimation From="1" To="0.5" Duration="0:0:0.5" /> <DoubleAnimation From="0.5" To="1" Duration="0:0:0.5" /> </Storyboard> </BeginStoryboard> </EventTrigger> <EventTrigger RoutedEvent="Mouse.MouseEnter"> <BeginStoryboard> <Storyboard TargetProperty="Width"> <DoubleAnimation From="80" To="95" Duration="0:0:0.2" /> </Storyboard> </BeginStoryboard> </EventTrigger> <Trigger Property="IsMouseOver" Value="True"> <Setter Property="Cursor" Value="Hand"/> </Trigger> </ControlTemplate.Triggers> </ControlTemplate> Button is as follows: <Button Template="{StaticResource IconButton}" Name="btnExit"> <Image Source="Images/Exit.png" /> </Button> The problem is that the width doesn't change when my mouse goes over. (Or at least - the width of the image does not...) I believe there is a "scale" transform I can use to enlarge the button and all it's contents? how would I do that here...? Thanks.

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• WPF Border DesiredHeight

  - by Joseph Sturtevant

  The following Microsoft example code contains the following: <Grid> ... <Border Name="Content" ... > ... </Border> </Grid> <ControlTemplate.Triggers> <Trigger Property="IsExpanded" Value="True"> <Setter TargetName="ContentRow" Property="Height" Value="{Binding ElementName=Content,Path=DesiredHeight}" /> </Trigger> ... </ControlTemplate.Triggers> When run, however, this code generates the following databinding error: System.Windows.Data Error: 39 : BindingExpression path error: 'DesiredHeight' property not found on 'object' ''Border' (Name='Content')'. BindingExpression:Path=DesiredHeight; DataItem='Border' (Name='Content'); target element is 'RowDefinition' (HashCode=2034711); target property is 'Height' (type 'GridLength') Despite this error, the code works correctly. I have looked through the documentation and DesiredHeight does not appear to be a member of Border. Can anyone explain where DesiredHeight is coming from? Also, is there any way to resolve/suppress this error so my program output is clean?

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• AdornedElement Properties in a Trigger

  - by Chris Nicol

  I have an Adorner in XAML that I'm using for ErrorValidation. Basically I have a grid that I want to display on two conditions (if the "AdornedElement" IsFocused or IsMouseOver). Below is a code snippet where I'm binding - successfully - to the IsFocused of the AdornedElement, but as you can tell that only solves 1/2 the conditions. Now I can't pass another binding into the converter, nor can I create a property that handles both (needs to be XAML only solution). <AdornedElementPlaceholder x:Name="errorAdorner" /> ... <Grid x:Name="ErrorDetails" Visibility="{Binding ElementName=errorAdorner, Path=AdornedElement.IsFocused, Converter={StaticResource BooleanToVisibilityConverter}}" /> ... What I want to do is use triggers to handle this, the only problem is I can't access the AdornedElement's properties on a trigger. Something like this ... <Trigger SourceName="errorAdorner" Property="AdornedElement.IsFocused" Value="True"> <Setter TargetName="ErrorDetails" Property="Visibility" Value="Visible" /> </Trigger> This would also help as part of what I want to do is trigger animations, rather than just setting the visibility. Any help would be great.

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• WPF: Selecting the Target of an Animation

  - by Phil Sandler

  I am trying to create a simple (I think) animation effect based on a property change in my ViewModel. I would like the target to be a specific textblock in the control template of a custom control, which inherits from Window. From the article examples I've seen, a DataTrigger is the easiest way to accomplish this. It appears that Window.Triggers doesn't support DataTriggers, which led me to try to apply the trigger in the style. The problem I am currently having is that I can't seem to target the TextBlock (or any other child control)--what happens is which the code below is that the animation is applied to the background of the whole window. If I leave off StoryBoard.Target completely, the effect is exactly the same. Is this the right approach with the wrong syntax, or is there an easier way to accomplish this? <Style x:Key="MyWindowStyle" TargetType="{x:Type Window}"> <Setter Property="Template" Value="{StaticResource MyWindowTemplate}"/> <Style.Triggers> <DataTrigger Binding="{Binding ChangeOccurred}" Value="True"> <DataTrigger.EnterActions> <BeginStoryboard> <Storyboard BeginTime="00:00:00" Duration="0:0:2" Storyboard.Target="{Binding RelativeSource={RelativeSource AncestorType=TextBlock}}" Storyboard.TargetProperty="(Background).(SolidColorBrush.Color)"> <ColorAnimation FillBehavior="Stop" From="Black" To="Red" Duration="0:0:0.5" AutoReverse="True"/> </Storyboard> </BeginStoryboard> </DataTrigger.EnterActions> </DataTrigger> </Style.Triggers> </Style>

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• PHP OOP: Providing Domain Entities with "Identity"

  - by sunwukung

  Bit of an abstract problem here. I'm experimenting with the Domain Model pattern, and barring my other tussles with dependencies - I need some advice on generating Identity for use in an Identity Map. In most examples for the Data Mapper pattern I've seen (including the one outlined in this book: http://apress.com/book/view/9781590599099) - the user appears to manually set the identity for a given Domain Object using a setter: $UserMapper = new UserMapper; //returns a fully formed user object from record sets $User = $UserMapper->find(1); //returns an empty object with appropriate properties for completion $UserBlank = $UserMapper->get(); $UserBlank->setId(); $UserBlank->setOtherProperties(); Now, I don't know if I'm reading the examples wrong - but in the first $User object, the $id property is retrieved from the data store (I'm assuming $id represents a row id). In the latter case, however, how can you set the $id for an object if it has not yet acquired one from the data store? The problem is generating a valid "identity" for the object so that it can be maintained via an Identity Map - so generating an arbitrary integer doesn't solve it. My current thinking is to nominate different fields for identity (i.e. email) and demanding their presence in generating blank Domain Objects. Alternatively, demanding all objects be fully formed, and using all properties as their identity...hardly efficient. (Or alternatively, dump the Domain Model concept and return to DBAL/DAO/Transaction Scripts...which is seeming increasingly elegant compared to the ORM implementations I've seen...)

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• What's the order of execution when using IDataErrorInfo?

  - by Benny Jobigan

  Many times with WPF, we use INotifyPropertyChanged and IDataErrorInfo to enable binding and validation on our data objects. I've got a lot of properties that look like this: public SomeObject SomeData { get { return _SomeData; } set { _SomeData = value; OnPropertyChanged("SomeData"); } } Of course, I have an appropriate overridden IDataErrorInfo.this[] in my class to do validation. Question 1) In a binding situation, what happens? For example: User enters new data. Binding writes data to property. Property set method is executed. Binding checks this[] for validation. If the data is invalid, the binding sets the property back to the old value. Property set method is executed again. This is important if you are adding "hooks" into the set method, like: public string PathToFile { get { return _PathToFile; } set { if (_PathToFile != value && // prevent unnecessary actions OnPathToFileChanging(value)) // allow subclasses to do something or stop the setter { _PathToFile = value; OnPathToFileChanged(); // allow subclasses to do something afterwards OnPropertyChanged("PathToFile"); } } }

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• How do you map a DateTime property to 2 varchar columns in the database with NHibernate (Fluent)?

  - by gabe

  I'm dealing with a legacy database that has date and time fields as char(8) columns (formatted yyyyMMdd and HH:mm:ss, respectively) in some of the tables. How can i map the 2 char columns to a single .NET DateTime property? I have tried the following, but i get a "can't access setter" error of course because DateTime Date and TimeOfDay properties are read-only: public class SweetPocoMannaFromHeaven { public virtual DateTime? FileCreationDateTime { get; set; } } . mapping.Component<DateTime?>(x => x.FileCreationDateTime, dt => { dt.Map(x => x.Value.Date, "file_creation_date"); dt.Map(x => x.Value.TimeOfDay, "file_creation_time"); }); I have also tried defining a IUserType for DateTime, but i can't figure it out. I've done a ton of googling for an answer, but i can't figure it out still. What is my best option to handle this stupid legacy database convention? A code example would be helpful since there's not much out for documentation on some of these more obscure scenarios.

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• How do I properly implement a property in F#?

  - by Greg D

  Consider my first attempt, a simple type in F# like the following: type Test() = inherit BaseImplementingNotifyPropertyChangedViaOnPropertyChanged() let mutable prop: string = null member this.Prop with public get() = prop and public set value = match value with | _ when value = prop -> () | _ -> let prop = value this.OnPropertyChanged("Prop") Now I test this via C# (this object is being exposed to a C# project, so apparent C# semantics are desirable): [TestMethod] public void TaskMaster_Test() { var target = new FTest(); string propName = null; target.PropertyChanged += (s, a) => propName = a.PropertyName; target.Prop = "newString"; Assert.AreEqual("Prop", propName); Assert.AreEqual("newString", target.Prop); return; } propName is properly assigned, my F# Setter is running, but the second assert is failing because the underlying value of prop isn't changed. This sort of makes sense to me, because if I remove mutable from the prop field, no error is generated (and one should be because I'm trying to mutate the value). I think I must be missing a fundamental concept. What's the correct way to rebind/mutate prop in the Test class so that I can pass my unit test?

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• Checked status not updated in CheckBox template

  - by Simon

  Hey there. I'm trying to create an hyperlink that changes its text depending on a boolean value. I thought I could leverage the IsChecked method of a CheckBox. So I wrote this ControlTemplate for a CheckBox: <CheckBox Checked="CheckBox_Checked" IsChecked="{Binding Path=SomeBool, Mode=TwoWay}"> <CheckBox.Template> <ControlTemplate TargetType="{x:Type CheckBox}"> <BulletDecorator> <BulletDecorator.Bullet> <TextBlock> <Hyperlink> <TextBlock x:Name="TextBoxHyperlink">Unchecked</TextBlock> </Hyperlink> </TextBlock> </BulletDecorator.Bullet> <ContentPresenter /> </BulletDecorator> <ControlTemplate.Triggers> <Trigger Property="IsChecked" Value="True"> <Setter TargetName="TextBoxHyperlink" Property="Text" Value="Checked" /> </Trigger> </ControlTemplate.Triggers> </ControlTemplate> </CheckBox.Template> </CheckBox> But when I click on the hyperlink, nothing happens. The checked status is not changed and the Text property of the TextBlock is not updated. Any ideas?

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• wpf error template - red box still visible on collapse of an expander

  - by Andy Clarke

  Hi, I'm doing some validation on the DataSource of TextBox that's within an Expander and have found that once a validation error has been triggered, if I collapse the Expander, the red box stays where the TextBox would have been. <Expander Header="Blah Blah Blah"> <TextBox Name="TextBox" Validation.ErrorTemplate="{DynamicResource TextBoxErrorTemplate}" Text="{Binding Path=Blah, UpdateSourceTrigger=PropertyChanged, ValidatesOnDataErrors=True}" /> </Expander> I've tried to get round this by binding the visibility of the Error Template to the Expander, however I think there's something wrong with the binding. <local:NotVisibleConverter x:Key="NotVisibleConverter" /> <ControlTemplate x:Key="TextBoxErrorTemplate"> <DockPanel> <Border BorderBrush="Red" BorderThickness="2" Visibility="{Binding Path=IsExpanded, Converter={StaticResource NotVisibleConverter}, RelativeSource={RelativeSource AncestorType=Expander}}" > <AdornedElementPlaceholder Name="MyAdorner" /> </Border> </DockPanel> <ControlTemplate.Triggers> <Trigger Property="Validation.HasError" Value="true"> <Setter Property="ToolTip" Value="{Binding RelativeSource={RelativeSource Self}, Path=(Validation.Errors)[0].ErrorContent}"/> </Trigger> </ControlTemplate.Triggers> </ControlTemplate> I guess I've gone wrong with my binding, can someone put me back on track please? Alternatively does anyone know another solution to the ErrorTemplate still being visible on the collapse of an Expander?

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• Problem with UserControl with custom Dependency Property

  - by Mathias Koch

  Hi, I'm writing a user control with a dependency property for a search text called SearchText. It is a dependency property because I want to allow consumers of the control to use data binding. The user control contains a WPF TextBox where the user can enter the search text. I could use data binding to connect the SearchText dependency property of the user control with the Text dependency property of the TextBox, but this binding only fires when the text box looses input focus. What I want is SearchText to be updated after every change of Text. So I have added a TextChanged event handler to the user control where I set SearchText to the value of Text. My Problem is, the SearchText binding doesn't work, the source never gets updated. What am I doing wrong? Here's the relevant part of the user controls code-behind: public partial class UserControlSearchTextBox : UserControl { public string SearchText { get { return (string)GetValue(SearchTextProperty); } set { SetValue(SearchTextProperty, value); } } public static readonly DependencyProperty SearchTextProperty = DependencyProperty.Register("SearchText", typeof(string), typeof(UserControlSearchTextBox), new UIPropertyMetadata("")); private void TextBox_TextChanged(object sender, TextChangedEventArgs e) { SearchText = ((TextBox)sender).Text; } ... } The window that contains an instance of the user control has its DataContext set to an object that has a property also called SearchText. <uc:UserControlSearchTextBox SearchText="{Binding SearchText}" /> The data context of the Window: public class DataSourceUserManual : DataSourceBase { private string _searchText; public string SearchText { get { return _searchText; } set { _searchText = value; ... OnPropertyChanged("SearchText"); } } } Unfortunately, this setter is not called when I type into the text box. Any ideas?

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• Is it possible from Spring to inject the result of calling a method on a ref bean?

  - by Alex Worden

  Hi, Is it possible from Spring to inject the result of calling a method on a ref bean? I'm trying to refactor some cut/pasted code from two separate projects into a common class. In one of the projects, the code lives in a class I'll call "MyClient" that is being instantiated from Spring. It is injected with another spring-instantiated class "MyRegistry", then the MyClient class uses that class to look up an endpoint. All I really need is the endpoint String in my refactored class, which can be initialized via a Setter. I really cannot have a dependency on MyRegistry from MyClient in the refactored code. So, my question is this... is there a way I can inject the endpoint String from spring that was looked up in the MyRegistry class. So, I currently have: <bean id="registryService" class="foo.MyRegistry"> ...properties set etc... </bean> <bean id="MyClient" class="foo.MyClient"> <property name="registry" ref="registryService"/> </bean> But I'd like to have (and I know this is imaginary Spring syntax) <bean id="MyClient" class="foo.MyClient"> <property name="endPoint" value="registryService.getEndPoint('bar')"/> </bean> where MyRegistry will have a method getEndPoint(Stirng endPointName) Hope that makes sense from a the standpoint of what I'm trying to achieve. Please let me know if something like this is possible in Spring!

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• Is NUnit's ExpectedExceptionAttribute only way to test if something raises an exception?

  - by Dariusz Walczak

  Hello, I'm completely new at C# and NUnit. In Boost.Test there is a family of BOOST_*_THROW macros. In Python's test module there is TestCase.assertRaises method. As far as I understand it, in C# with NUnit (2.4.8) the only method of doing exception test is to use ExpectedExceptionAttribute. Why should I prefer ExpectedExceptionAttribute over - let's say - Boost.Test's approach? What reasoning can stand behind this design decision? Why is that better in case of C# and NUnit? Finally, if I decide to use ExpectedExceptionAttribute, how can I do some additional tests after exception was raised and catched? Let's say that I want to test requirement saying that object has to be valid after some setter raised System.IndexOutOfRangeException. How would you fix following code to compile and work as expected? [Test] public void TestSetterException() { Sth.SomeClass obj = new SomeClass(); // Following statement won't compile. Assert.Raises( "System.IndexOutOfRangeException", obj.SetValueAt( -1, "foo" ) ); Assert.IsTrue( obj.IsValid() ); } Edit: Thanks for your answers. Today, I've found an It's the Tests blog entry where all three methods described by you are mentioned (and one more minor variation). It's shame that I couldn't find it before :-(.

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• Setting WPF control background image using styles?

  - by aviv

  Hi, I have a set of buttons inside a stack panel. I want them all to have a background image. How can i do it using styles? since i don't want to set manually the Background image for each button. Here is a code snippet: <StackPanel Orientation="Horizontal" Height="100px" VerticalAlignment="Top"> <StackPanel.Resources> <Style TargetType="Button"> <Setter Property="Margin" Value="2,4" /> </Style> </StackPanel.Resources> <Button Width="127px" Height="79px" VerticalAlignment="Bottom"> <Button.Background> <ImageBrush ImageSource="images/Tab.png" /> </Button.Background> </Button> <Button>A</Button> <Button>R</Button> <Button>S</Button> </StackPanel> Thanks.

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• How to do binding programmically?

  - by user175908

  Hello, Could anyone identify the problem in this code? (I'm kinda newbie in WPF bindings.) This code executes after chart is loaded when I click a button: I get this error: Update: I dont get that error anymore. Thanks to Tomas. Now no error occur but chart looks completely blank (no columns) Update: Code now looks like this: // create a very simple DataSet var dataSet = new DataSet("MyDataSet"); var table = dataSet.Tables.Add("MyTable"); table.Columns.Add("Name"); table.Columns.Add("Price"); table.Rows.Add("Brick", 1.5d); table.Rows.Add("Soap", 4.99d); table.Rows.Add("Comic Book", 0.99d); // chart series var series = new ColumnSeries() { IndependentValueBinding = new Binding("[Name]"), // How to deal with DependentValueBinding = new Binding("[Price]"), // these two? ItemsSource = dataSet.Tables[0].DefaultView // or maybe I do mistake here? }; // ---------- set additional binding as adviced ------------------ series.SetBinding(ColumnSeries.ItemsSourceProperty, new Binding()); // chart stuff MyChart.Series.Add(series); MyChart.Title = "Names 'n Prices"; // some code to remove legend var style = new Style(typeof(Control)); style.Setters.Add(new Setter(LegendItem.TemplateProperty, null)); MyChart.LegendStyle = style; XAML: <Window x:Class="BindingzTest.MainWindow" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" Title="MainWindow" Height="606" Width="988" xmlns:charting="clr-namespace:System.Windows.Controls.DataVisualization.Charting;assembly=System.Windows.Controls.DataVisualization.Toolkit"> <Grid Name="LayoutRoot"> <charting:Chart Name="MyChart" Margin="0,0,573,0" Height="289" VerticalAlignment="Top" /> <Button Content="Button" Height="23" HorizontalAlignment="Left" Margin="272,361,0,0" Name="button1" VerticalAlignment="Top" Width="75" Click="chart1_Loaded" /> </Grid> Thanks for help in advance once more.

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• WPF ContextMenu bind some property to another property of the same control

  - by bebicasoft

  I have a ContextMenu and a ColumnHeaderStyle defined in Window.Resource section witch i use-it to a DataGrid ColumnHeader. My code is something like this: <ContextMenu x:Key="cm_columnHeaderMenu"/> <Style x:Key="DefaultColumnHeaderStyle" TargetType="{x:Type DataGridColumnHeader}"> <Setter Property="ContextMenu" Value="{StaticResource cm_columnHeaderMenu}" /> </Style> <DataGrid Grid.Column="2" Grid.Row="1" x:Name="dgridFiles" IsReadOnly="True" ColumnHeaderStyle="{StaticResource DefaultColumnHeaderStyle}"> I want to know if I can (and if the answer it true, then HOW I could do it) bind the ContextMenu Visibility property to same control ContextMenu Items.Count>0 property. Initially based on some other treeView control selections made there shoud be no items in the context menu, but i wish to add dinamically items in ContextMenu based on selection in treeView. This part is done, the context has those items. On some selections there are no-items, but still on the grid it appears an empty ContextMenu. So I believe the easiest part it would be to bind the Visibility to Items.Count property of the same control. Sorry if my english is not good enought, I'll try to explain better if i didnt make clear 1st time.

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• Pointers, am I doing them correctly? Objective-c/cocoa

  - by Chris

  I have this in my @interface struct track currentTrack; struct track previousTrack; int anInt; Since these are not objects, I do not have to have them like int* anInt right? And if setting non-object values like ints, boolean, etc, I do not have to release the old value right (assuming non-GC environment)? The struct contains objects: typedef struct track { NSString* theId; NSString* title; } *track; Am I doing that correctly? Lastly, I access the struct like this: [currentTrack.title ...]; currentTrack.theId = @"asdf"; //LINE 1 I'm also manually managing the memory (from a setter) for the struct like this: [currentTrack.title autorelease]; currentTrack.title = [newTitle retain]; If I'm understanding the garbage collection correctly, I should be able to ditch that and just set it like LINE 1 (above)? Also with garbage collection, I don't need a dealloc method right? If I use garbage collection does this mean it only runs on OS 10.5+? And any other thing I should know before I switch to garbage collected code? Sorry there are so many questions. Very new to objective-c and desktop programming. Thanks

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• How can I bind another DependencyProperty to the IsChecked Property of a CheckBox?

  - by speedmetal

  Here's an example of what I'm trying to accomplish: <Window x:Class="CheckBoxBinding.MainWindow" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" Title="MainWindow" Height="350" Width="525"> <StackPanel> <CheckBox Name="myCheckBox">this</CheckBox> <Grid> <Grid.Resources> <Style TargetType="ListBox"> <Style.Triggers> <Trigger Property="{Binding ElementName=myCheckBox, Path=IsChecked}" Value="True"> <Setter Property="Background" Value="Red" /> </Trigger> </Style.Triggers> </Style> </Grid.Resources> <ListBox> <ListBoxItem>item</ListBoxItem> <ListBoxItem>another</ListBoxItem> </ListBox> </Grid> </StackPanel> </Window> When I try to run it, I get this XamlParseException: A 'Binding' cannot be set on the 'Property' property of type 'Trigger'. A 'Binding' can only be set on a DependencyProperty of a DependencyObject. So how can I bind a property on the ListBox to the IsChecked property of a CheckBox?

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• How do I reference my MainViewController from another class?

  - by todd412

  Hi, I am building an iPhone Utility app that uses UIImageView to display an animation. Within the MainViewController's viewDidLoad() method, I am creating an instance of a CustomClass, and then setting up the animations: - (void)viewDidLoad { [super viewDidLoad]; cc = [CustomClass new]; NSArray * imageArray = [[NSArray alloc] initWithObjects: [UIImage imageNamed:@"image-1-off.jpg"], [UIImage imageNamed:@"image-2-off.jpg"], [UIImage imageNamed:@"image-3-off.jpg"], [UIImage imageNamed:@"image-4-off.jpg"], nil]; offSequence = [[UIImageView alloc] initWithFrame:CGRectMake(0, 0, 320, 480)]; offSequence.animationImages = imageArray; offSequence.animationDuration = .8; offSequence.contentMode = UIViewContentModeBottomLeft; [self.view addSubview:offSequence]; [offSequence startAnimating]; } That works fine. However, I would like to be able to move all the above code that sets up the UIImageView into my CustomClass. The problem is in the second to last line: [self.view addSubview:offSequence]; I basically need to replace 'self' with a reference to the MainControllerView, so I can call addSubview from within my CustomClass. I tried creating an instance var of CustomClass called mvc and a setter method that takes a reference to the MainViewController as an argument as such: - (void) setMainViewController: (MainViewController *) the_mvc { mvc = the_mvc; } And then I called it within MainViewController like so: [cc setMainController:MainViewController:self]; But this yields all sorts of errors which I can post here, but it strikes me that I may be overcomplicating this. Is there an easier way to reference the MainViewController that instanatiated my CustomClass?

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• Logic for family tree program

  - by david robers

  Hi All, I am creating a family tree program in Java, or at least trying to. I have developed several classes: Person - getters and setter for name gender age etc FamilyMember - extends Person getters and setters for setting arents and children Family - which consists of multiple family members and methods for adding removing members FamilyTree which is the main class for setting relationships. I have two main problems: 1) I need to set the relationships between people. Currently I am doing: FamilyMember A, FamilyMember B B.setMother(A); A.setChild(B); The example above is for setting a mother child relationship. This seems very clunky. Its getting very long winded to implement all relationships. Any ideas on how to implement multiple relationships in a less prodcedural way? 2) I have to be able to display the family tree. How can I do this? Are there any custom classes out there to make life easier? Thanks for your time...

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• wpf observableCollection

  - by Asha

  I have an ObservableCollection which is dataContext for my treeview when I try to remove an Item from ObservableCollection I will get an error that Object reference not set to an instance of an object . can you please tell me why this error is happening and what is the solution thanks EDIT 1: The code is something like : class MyClass : INotifyPropertyChanged { //my class code here } public partial class UC_myUserControl : UserControl { private ObservableCollection<MyClass> myCollection = new ObservableCollection<MyClass>(); private void UserControl_Loaded(object sender, RoutedEventArgs e) { myCollection.add(new myClass); myTreeView.DataContext = myCollection ; } private void deleteItem() { myCollection.RemoveAt(0); //after removing I get error Which I guess should be something related //to interface update but I don't know how can I solve it } } Exception Detail : System.NullReferenceException was unhandled Message="Object reference not set to an instance of an object." Source="PresentationFramework" EDIT 3: I have a style which is for my treeitem to keep the treeitems expanded <Style TargetType="TreeViewItem"> <Setter Property="IsExpanded" Value="True" /> </Style> and with commenting this part I wont get any error !!! Now I want to change my question to why having this style is causing error ?

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• Reverse mapping from a table to a model in SQLAlchemy

  - by Jace

  To provide an activity log in my SQLAlchemy-based app, I have a model like this: class ActivityLog(Base): __tablename__ = 'activitylog' id = Column(Integer, primary_key=True) activity_by_id = Column(Integer, ForeignKey('users.id'), nullable=False) activity_by = relation(User, primaryjoin=activity_by_id == User.id) activity_at = Column(DateTime, default=datetime.utcnow, nullable=False) activity_type = Column(SmallInteger, nullable=False) target_table = Column(Unicode(20), nullable=False) target_id = Column(Integer, nullable=False) target_title = Column(Unicode(255), nullable=False) The log contains entries for multiple tables, so I can't use ForeignKey relations. Log entries are made like this: doc = Document(name=u'mydoc', title=u'My Test Document', created_by=user, edited_by=user) session.add(doc) session.flush() # See note below log = ActivityLog(activity_by=user, activity_type=ACTIVITY_ADD, target_table=Document.__table__.name, target_id=doc.id, target_title=doc.title) session.add(log) This leaves me with three problems: I have to flush the session before my doc object gets an id. If I had used a ForeignKey column and a relation mapper, I could have simply called ActivityLog(target=doc) and let SQLAlchemy do the work. Is there any way to work around needing to flush by hand? The target_table parameter is too verbose. I suppose I could solve this with a target property setter in ActivityLog that automatically retrieves the table name and id from a given instance. Biggest of all, I'm not sure how to retrieve a model instance from the database. Given an ActivityLog instance log, calling self.session.query(log.target_table).get(log.target_id) does not work, as query() expects a model as parameter. One workaround appears to be to use polymorphism and derive all my models from a base model which ActivityLog recognises. Something like this: class Entity(Base): __tablename__ = 'entities' id = Column(Integer, primary_key=True) title = Column(Unicode(255), nullable=False) edited_at = Column(DateTime, onupdate=datetime.utcnow, nullable=False) entity_type = Column(Unicode(20), nullable=False) __mapper_args__ = {'polymorphic_on': entity_type} class Document(Entity): __tablename__ = 'documents' __mapper_args__ = {'polymorphic_identity': 'document'} body = Column(UnicodeText, nullable=False) class ActivityLog(Base): __tablename__ = 'activitylog' id = Column(Integer, primary_key=True) ... target_id = Column(Integer, ForeignKey('entities.id'), nullable=False) target = relation(Entity) If I do this, ActivityLog(...).target will give me a Document instance when it refers to a Document, but I'm not sure it's worth the overhead of having two tables for everything. Should I go ahead and do it this way?

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• Windows 8 Data Binding Bug - OnPropertyChanged Updates Wrong Object

  - by Andrew

  I'm experiencing some really weird behavior with data binding in Windows 8. I have a combobox set up like this: <ComboBox VerticalAlignment="Center" Margin="0,18,0,0" HorizontalAlignment="Right" Height="Auto" Width="138" Background="{StaticResource DarkBackgroundBrush}" BorderThickness="0" ItemsSource="{Binding CurrentForum.SortValues}" SelectedItem="{Binding CurrentForum.CurrentSort, Mode=TwoWay}"> <ComboBox.ItemTemplate> <DataTemplate> <TextBlock HorizontalAlignment="Right" Text="{Binding Converter={StaticResource SortValueConverter}}"/> </DataTemplate> </ComboBox.ItemTemplate> </ComboBox> Inside of a page with the DataContext set to a statically located ViewModel. When I change that ViewModel's CurrentForm attribute, who's property is implemented like this... public FormViewModel CurrentForm { get { return _currentForm; } set { _currentForm = value; if (!_currentForm.IsLoaded) { _currentSubreddit.Refresh.Execute(null); } RaisePropertyChanged("CurrentForm"); } } ... something really strange happens. The previous FormViewModel's CurrentSort property is changed to the new FormViewModel's current sort property. This happens as the RaisePropertyChanged event is called, through a managed-to-native transition, with native code invoking the setter of CurrentSort of the previous FormViewModel. Does that sound like a bug in Win8's data binding? Am I doing something wrong?

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• Strange JPA one-to-many behavior when trying to set the "many" on the "one" entity

  - by errr

  I've mapped two entities using JPA (specifically Hibernate). Those entities have a one-to-many relationship (I've simplified for presentation): @Entity public class A { @ManyToOne public B getB() { return b; } } @Entity public Class B { @OneToMany(mappedBy="b") public Set<A> getAs() { return as; } } Now, I'm trying to create a relationship between two instances of these entities by using the setter of the one-side/not-owner-side of the relationship (i.e the table being referenced to): em.getTransaction().begin(); A a = new A(); B b = new B(); Set<A> as = new HashSet<A>(); as.add(a); b.setAs(as); em.persist(a); em.persist(b); em.getTransaction().commit(); But then, the relationship isn't persisted to the DB (the row created for entity A isn't referencing the row created for entity B). Why is it so? I'd excpect it to work. Also, if I remove the "mappedBy" property from the @OneToMany annotation it will work. Again - why is it so? and what are the possible effects for removing the "mappedBy" property?

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• WPF ResourceDictionary and DynamicResource

  - by lanicor

  i am new to WPF so maybe this will be "noob" question but i can't find answer to it (and it seems so easy)... well i am programing WPF app and i want to use smth similar to css for webpages, so i found ResourceDictionary and tried to use it... I have main window in which i create Frame and on click some UserControl is loaded to that same Frame.I include my ResourceDictionary (root/style/Styles.xaml) to my main window like this: <Window.Resources> <ResourceDictionary x:Key="styles" Source="style/Styles.xaml" /> </Window.Resources> in which i have: <ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"> <Style x:Key="ProductsRequired" TargetType="{x:Type Label}"> <Setter Property="Height" Value="28" /> ... I don't use it on my main window but want to use it on my UserControls, which are loaded to that main window and i try to use it like this: <Label Name="product1" Style="{DynamicResource ProductsRequired}" /> Warning i am getting all the time is: The resource "ProductsRequired" could not be resolved. I even tried including Styles to my UserControl <UserControl.Resources> <ResourceDictionary x:Key="styles" Source="../style/Styles.xaml" /> </UserControl.Resources> and nothing happens... Well my question is long but i wanted to be clear... :) P.S. all that logic works in C# code btw private ResourceDictionary myStyles = new ResourceDictionary(); Style ProductsRequired = myStyles["ProductsRequired"] as Style; product1.Style = ProductsRequired;

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