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Paging Through Records(json data) Using jQuery...

- by Pandiya Chendur

I have a JSON result that contains numerous records. I'd like to show the first five records in one page and create pager links which have to move to that page with five record so on. I don't want the page to refresh which is why I'm hoping a combination of JavaScript and jQuery... My json Data looks like this... {"Table" : [{"Emp_Id" : "3","Identity_No" : "","Emp_Name" : "Jerome","Address" : "Madurai","Date_Of_Birth" : "","Desig_Name" : "Supervisior","Desig_Description" : "Supervisior of the Construction","SalaryBasis" : "Monthly","FixedSalary" : "25000.00"},{"Emp_Id" : "4","Identity_No" : "","Emp_Name" : "Mohan","Address" : "Madurai","Date_Of_Birth" : "","Desig_Name" : "Acc ","Desig_Description" : "Accountant","SalaryBasis" : "Monthly","FixedSalary" : "200.00"},{"Emp_Id" : "5","Identity_No" : "","Emp_Name" : "Murugan","Address" : "Madurai","Date_Of_Birth" : "","Desig_Name" : "Mason","Desig_Description" : "Mason","SalaryBasis" : "Weekly","FixedSalary" : "150.00"},{"Emp_Id" : "6","Identity_No" : "","Emp_Name" : "Ram","Address" : "Madurai","Date_Of_Birth" : "","Desig_Name" : "Mason","Desig_Description" : "Mason","SalaryBasis" : "Weekly","FixedSalary" : "120.00"},{"Emp_Id" : "7","Identity_No" : "","Emp_Name" : "Raja","Address" : "Madurai","Date_Of_Birth" : "","Desig_Name" : "Mason","Desig_Description" : "Mason","SalaryBasis" : "Weekly","FixedSalary" : "135.00"},{"Emp_Id" : "8","Identity_No" : "","Emp_Name" : "Raja kumar","Address" : "Madurai","Date_Of_Birth" : "","Desig_Name" : "Mason Helper","Desig_Description" : "Mason Helper","SalaryBasis" : "Weekly","FixedSalary" : "105.00"},{"Emp_Id" : "9","Identity_No" : "","Emp_Name" : "Lakshmi","Address" : "Madurai","Date_Of_Birth" : "","Desig_Name" : "Mason Helper","Desig_Description" : "Mason Helper","SalaryBasis" : "Weekly","FixedSalary" : "100.00"},{"Emp_Id" : "10","Identity_No" : "","Emp_Name" : "Palani","Address" : "Madurai","Date_Of_Birth" : "","Desig_Name" : "Carpenter","Desig_Description" : "Carpenter","SalaryBasis" : "Weekly","FixedSalary" : "200.00"},{"Emp_Id" : "11","Identity_No" : "","Emp_Name" : "Annamalai","Address" : "Madurai","Date_Of_Birth" : "","Desig_Name" : "Carpenter","Desig_Description" : "Carpenter","SalaryBasis" : "Weekly","FixedSalary" : "220.00"},{"Emp_Id" : "12","Identity_No" : "","Emp_Name" : "David","Address" : "Madurai","Date_Of_Birth" : "","Desig_Name" : "Steel Fixer","Desig_Description" : "Steel Fixer","SalaryBasis" : "Weekly","FixedSalary" : "220.00"},{"Emp_Id" : "13","Identity_No" : "","Emp_Name" : "Chandru","Address" : "Madurai","Date_Of_Birth" : "","Desig_Name" : "Steel Fixer","Desig_Description" : "Steel Fixer","SalaryBasis" : "Weekly","FixedSalary" : "220.00"},{"Emp_Id" : "14","Identity_No" : "","Emp_Name" : "Mani","Address" : "Madurai","Date_Of_Birth" : "","Desig_Name" : "Steel Helper","Desig_Description" : "Steel Helper","SalaryBasis" : "Weekly","FixedSalary" : "175.00"},{"Emp_Id" : "15","Identity_No" : "","Emp_Name" : "Karthik","Address" : "Madurai","Date_Of_Birth" : "","Desig_Name" : "Wood Fixer","Desig_Description" : "Wood Fixer","SalaryBasis" : "Weekly","FixedSalary" : "195.00"},{"Emp_Id" : "16","Identity_No" : "","Emp_Name" : "Bala","Address" : "Madurai","Date_Of_Birth" : "","Desig_Name" : "Wood Fixer","Desig_Description" : "Wood Fixer","SalaryBasis" : "Weekly","FixedSalary" : "185.00"},{"Emp_Id" : "17","Identity_No" : "","Emp_Name" : "Tamil arasi","Address" : "Madurai","Date_Of_Birth" : "","Desig_Name" : "Wood Helper","Desig_Description" : "Wood Helper","SalaryBasis" : "Weekly","FixedSalary" : "185.00"},{"Emp_Id" : "18","Identity_No" : "","Emp_Name" : "Perumal","Address" : "Madurai","Date_Of_Birth" : "","Desig_Name" : "Cook","Desig_Description" : "Cook","SalaryBasis" : "Weekly","FixedSalary" : "105.00"},{"Emp_Id" : "19","Identity_No" : "","Emp_Name" : "Andiappan","Address" : "Madurai","Date_Of_Birth" : "","Desig_Name" : "Watchman","Desig_Description" : "Watchman","SalaryBasis" : "Weekly","FixedSalary" : "150.00"}]} And as of now my result looks like this, http://img401.imageshack.us/img401/2500/yuidtsum.jpg I have used jquery for this, var jsonObj = JSON.parse(HfJsonValue); for (var i = jsonObj.Table.length - 1; i >= 0; i--) { var employee = jsonObj.Table[i]; $('<div class="resultsdiv"> ' + employee.Emp_Name + 'Category : ' + employee.Desig_Name + ' Salary Basis : ' + employee.SalaryBasis + 'Salary : ' + employee.FixedSalary + 'Address : ' + employee.Address + '</div>').insertAfter('#ResultsDiv'); } My image contains only 6 records as of now.. Any suggestions?

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Java Builder pattern with Generic type bounds

- by I82Much

Hi all, I'm attempting to create a class with many parameters, using a Builder pattern rather than telescoping constructors. I'm doing this in the way described by Joshua Bloch's Effective Java, having private constructor on the enclosing class, and a public static Builder class. The Builder class ensures the object is in a consistent state before calling build(), at which point it delegates the construction of the enclosing object to the private constructor. Thus public class Foo { // Many variables private Foo(Builder b) { // Use all of b's variables to initialize self } public static final class Builder { public Builder(/* required variables */) { } public Builder var1(Var var) { // set it return this; } public Foo build() { return new Foo(this); } } } I then want to add type bounds to some of the variables, and thus need to parametrize the class definition. I want the bounds of the Foo class to be the same as that of the Builder class. public class Foo<Q extends Quantity> { private final Unit<Q> units; // Many variables private Foo(Builder<Q> b) { // Use all of b's variables to initialize self } public static final class Builder<Q extends Quantity> { private Unit<Q> units; public Builder(/* required variables */) { } public Builder units(Unit<Q> units) { this.units = units; return this; } public Foo build() { return new Foo<Q>(this); } } } This compiles fine, but the compiler is allowing me to do things I feel should be compiler errors. E.g. public static final Foo.Builder<Acceleration> x_Body_AccelField = new Foo.Builder<Acceleration>() .units(SI.METER) .build(); Here the units argument is not Unit<Acceleration> but Unit<Length>, but it is still accepted by the compiler. What am I doing wrong here? I want to ensure at compile time that the unit types match up correctly.

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How to improve the builder pattern?

- by tangens

Motivation Recently I searched for a way to initialize a complex object without passing a lot of parameter to the constructor. I tried it with the builder pattern, but I don't like the fact, that I'm not able to check at compile time if I really set all needed values. Traditional builder pattern When I use the builder pattern to create my Complex object, the creation is more "typesafe", because it's easier to see what an argument is used for: new ComplexBuilder() .setFirst( "first" ) .setSecond( "second" ) .setThird( "third" ) ... .build(); But now I have the problem, that I can easily miss an important parameter. I can check for it inside the build() method, but that is only at runtime. At compile time there is nothing that warns me, if I missed something. Enhanced builder pattern Now my idea was to create a builder, that "reminds" me if I missed a needed parameter. My first try looks like this: public class Complex { private String m_first; private String m_second; private String m_third; private Complex() {} public static class ComplexBuilder { private Complex m_complex; public ComplexBuilder() { m_complex = new Complex(); } public Builder2 setFirst( String first ) { m_complex.m_first = first; return new Builder2(); } public class Builder2 { private Builder2() {} Builder3 setSecond( String second ) { m_complex.m_second = second; return new Builder3(); } } public class Builder3 { private Builder3() {} Builder4 setThird( String third ) { m_complex.m_third = third; return new Builder4(); } } public class Builder4 { private Builder4() {} Complex build() { return m_complex; } } } } As you can see, each setter of the builder class returns a different internal builder class. Each internal builder class provides exactly one setter method and the last one provides only a build() method. Now the construction of an object again looks like this: new ComplexBuilder() .setFirst( "first" ) .setSecond( "second" ) .setThird( "third" ) .build(); ...but there is no way to forget a needed parameter. The compiler wouldn't accept it. Optional parameters If I had optional parameters, I would use the last internal builder class Builder4 to set them like a "traditional" builder does, returning itself. Questions Is this a well known pattern? Does it have a special name? Do you see any pitfalls? Do you have any ideas to improve the implementation - in the sense of fewer lines of code?

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Test first subnode from node.

- by Kalinin

XML: <cont> <mode> <submode>lorem ipsum</submode> <submode>lorem ipsum</submode> <submode>lorem ipsum</submode> <submode>lorem ipsum</submode> <submode>lorem ipsum</submode> <submode>lorem ipsum</submode> <submode>lorem ipsum</submode> </mode> <mode> <submode>lorem ipsum</submode> <submode>lorem ipsum</submode> <submode>lorem ipsum</submode> <submode>lorem ipsum</submode> <submode>lorem ipsum</submode> <submode>lorem ipsum</submode> <submode>lorem ipsum</submode> </mode> <mode> <submode>lorem ipsum</submode> <submode>lorem ipsum</submode> <submode>lorem ipsum</submode> <submode>lorem ipsum</submode> <submode>lorem ipsum</submode> <submode>lorem ipsum</submode> <submode>lorem ipsum</submode> </mode> </cont> How to test first <submode> from each <mode> in such construction: <xsl:template match="submode"> <xsl:if test="(parent::mode) and (...what?...)"> ... </xsl:if> ... </xsl:template> I do not understand how use position() here.

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Good jquery pagination plugin to use with json Data...

- by bala3569

I am looking for a good jquery pagination plugin to use in my aspx page.... I have the following parameters currentpage,pagesize,TotalRecords,NumberofPages... I would like my plugin to same as stackoverflow paging .... EDIT: It should paginate through json data.... similar to this I use my json data and iterating with jquery var jsonObj = jQuery.parseJSON(HfJsonValue); for (var i = jsonObj.Table.length - 1; i >= 0; i--) { var employee = jsonObj.Table[i]; $('<div class="resultsdiv"> ' + employee.Emp_Name + 'Category : ' + employee.Desig_Name + ' Salary Basis : ' + employee.SalaryBasis + 'Salary : ' + employee.FixedSalary + 'Address : ' + employee.Address + '</div>').insertAfter('#ResultsDiv'); } There are 25 divs in my page as a result i want to show first five divs in page 1 and so on... Any suggestion... My HfJsonValue contains the following json data {"Table" : [{"Emp_Id" : "3","Identity_No" : "","Emp_Name" : "Jerome","Address" : "Madurai","Date_Of_Birth" : "","Desig_Name" : "Supervisior","Desig_Description" : "Supervisior of the Construction","SalaryBasis" : "Monthly","FixedSalary" : "25000.00"},{"Emp_Id" : "4","Identity_No" : "","Emp_Name" : "Mohan","Address" : "Madurai","Date_Of_Birth" : "","Desig_Name" : "Acc ","Desig_Description" : "Accountant","SalaryBasis" : "Monthly","FixedSalary" : "200.00"},{"Emp_Id" : "5","Identity_No" : "","Emp_Name" : "Murugan","Address" : "Madurai","Date_Of_Birth" : "","Desig_Name" : "Mason","Desig_Description" : "Mason","SalaryBasis" : "Weekly","FixedSalary" : "150.00"},{"Emp_Id" : "6","Identity_No" : "","Emp_Name" : "Ram","Address" : "Madurai","Date_Of_Birth" : "","Desig_Name" : "Mason","Desig_Description" : "Mason","SalaryBasis" : "Weekly","FixedSalary" : "120.00"},{"Emp_Id" : "7","Identity_No" : "","Emp_Name" : "Raja","Address" : "Madurai","Date_Of_Birth" : "","Desig_Name" : "Mason","Desig_Description" : "Mason","SalaryBasis" : "Weekly","FixedSalary" : "135.00"},{"Emp_Id" : "8","Identity_No" : "","Emp_Name" : "Raja kumar","Address" : "Madurai","Date_Of_Birth" : "","Desig_Name" : "Mason Helper","Desig_Description" : "Mason Helper","SalaryBasis" : "Weekly","FixedSalary" : "105.00"},{"Emp_Id" : "9","Identity_No" : "","Emp_Name" : "Lakshmi","Address" : "Madurai","Date_Of_Birth" : "","Desig_Name" : "Mason Helper","Desig_Description" : "Mason Helper","SalaryBasis" : "Weekly","FixedSalary" : "100.00"},{"Emp_Id" : "10","Identity_No" : "","Emp_Name" : "Palani","Address" : "Madurai","Date_Of_Birth" : "","Desig_Name" : "Carpenter","Desig_Description" : "Carpenter","SalaryBasis" : "Weekly","FixedSalary" : "200.00"},{"Emp_Id" : "11","Identity_No" : "","Emp_Name" : "Annamalai","Address" : "Madurai","Date_Of_Birth" : "","Desig_Name" : "Carpenter","Desig_Description" : "Carpenter","SalaryBasis" : "Weekly","FixedSalary" : "220.00"},{"Emp_Id" : "12","Identity_No" : "","Emp_Name" : "David","Address" : "Madurai","Date_Of_Birth" : "","Desig_Name" : "Steel Fixer","Desig_Description" : "Steel Fixer","SalaryBasis" : "Weekly","FixedSalary" : "220.00"},{"Emp_Id" : "13","Identity_No" : "","Emp_Name" : "Chandru","Address" : "Madurai","Date_Of_Birth" : "","Desig_Name" : "Steel Fixer","Desig_Description" : "Steel Fixer","SalaryBasis" : "Weekly","FixedSalary" : "220.00"},{"Emp_Id" : "14","Identity_No" : "","Emp_Name" : "Mani","Address" : "Madurai","Date_Of_Birth" : "","Desig_Name" : "Steel Helper","Desig_Description" : "Steel Helper","SalaryBasis" : "Weekly","FixedSalary" : "175.00"},{"Emp_Id" : "15","Identity_No" : "","Emp_Name" : "Karthik","Address" : "Madurai","Date_Of_Birth" : "","Desig_Name" : "Wood Fixer","Desig_Description" : "Wood Fixer","SalaryBasis" : "Weekly","FixedSalary" : "195.00"},{"Emp_Id" : "16","Identity_No" : "","Emp_Name" : "Bala","Address" : "Madurai","Date_Of_Birth" : "","Desig_Name" : "Wood Fixer","Desig_Description" : "Wood Fixer","SalaryBasis" : "Weekly","FixedSalary" : "185.00"},{"Emp_Id" : "17","Identity_No" : "","Emp_Name" : "Tamil arasi","Address" : "Madurai","Date_Of_Birth" : "","Desig_Name" : "Wood Helper","Desig_Description" : "Wood Helper","SalaryBasis" : "Weekly","FixedSalary" : "185.00"},{"Emp_Id" : "18","Identity_No" : "","Emp_Name" : "Perumal","Address" : "Madurai","Date_Of_Birth" : "","Desig_Name" : "Cook","Desig_Description" : "Cook","SalaryBasis" : "Weekly","FixedSalary" : "105.00"},{"Emp_Id" : "19","Identity_No" : "","Emp_Name" : "Andiappan","Address" : "Madurai","Date_Of_Birth" : "","Desig_Name" : "Watchman","Desig_Description" : "Watchman","SalaryBasis" : "Weekly","FixedSalary" : "150.00"}]}

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How to use jquery to paginate json data?

- by Pandiya Chendur

My json Data looks like this {"Table" : [{"Emp_Id" : "3","Identity_No" : "","Emp_Name" : "Jerome","Address" : "Madurai","Date_Of_Birth" : "","Desig_Name" : "Supervisior","Desig_Description" : "Supervisior of the Construction","SalaryBasis" : "Monthly","FixedSalary" : "25000.00"},{"Emp_Id" : "4","Identity_No" : "","Emp_Name" : "Mohan","Address" : "Madurai","Date_Of_Birth" : "","Desig_Name" : "Acc ","Desig_Description" : "Accountant","SalaryBasis" : "Monthly","FixedSalary" : "200.00"},{"Emp_Id" : "5","Identity_No" : "","Emp_Name" : "Murugan","Address" : "Madurai","Date_Of_Birth" : "","Desig_Name" : "Mason","Desig_Description" : "Mason","SalaryBasis" : "Weekly","FixedSalary" : "150.00"},{"Emp_Id" : "6","Identity_No" : "","Emp_Name" : "Ram","Address" : "Madurai","Date_Of_Birth" : "","Desig_Name" : "Mason","Desig_Description" : "Mason","SalaryBasis" : "Weekly","FixedSalary" : "120.00"},{"Emp_Id" : "7","Identity_No" : "","Emp_Name" : "Raja","Address" : "Madurai","Date_Of_Birth" : "","Desig_Name" : "Mason","Desig_Description" : "Mason","SalaryBasis" : "Weekly","FixedSalary" : "135.00"},{"Emp_Id" : "8","Identity_No" : "","Emp_Name" : "Raja kumar","Address" : "Madurai","Date_Of_Birth" : "","Desig_Name" : "Mason Helper","Desig_Description" : "Mason Helper","SalaryBasis" : "Weekly","FixedSalary" : "105.00"},{"Emp_Id" : "9","Identity_No" : "","Emp_Name" : "Lakshmi","Address" : "Madurai","Date_Of_Birth" : "","Desig_Name" : "Mason Helper","Desig_Description" : "Mason Helper","SalaryBasis" : "Weekly","FixedSalary" : "100.00"},{"Emp_Id" : "10","Identity_No" : "","Emp_Name" : "Palani","Address" : "Madurai","Date_Of_Birth" : "","Desig_Name" : "Carpenter","Desig_Description" : "Carpenter","SalaryBasis" : "Weekly","FixedSalary" : "200.00"},{"Emp_Id" : "11","Identity_No" : "","Emp_Name" : "Annamalai","Address" : "Madurai","Date_Of_Birth" : "","Desig_Name" : "Carpenter","Desig_Description" : "Carpenter","SalaryBasis" : "Weekly","FixedSalary" : "220.00"},{"Emp_Id" : "12","Identity_No" : "","Emp_Name" : "David","Address" : "Madurai","Date_Of_Birth" : "","Desig_Name" : "Steel Fixer","Desig_Description" : "Steel Fixer","SalaryBasis" : "Weekly","FixedSalary" : "220.00"},{"Emp_Id" : "13","Identity_No" : "","Emp_Name" : "Chandru","Address" : "Madurai","Date_Of_Birth" : "","Desig_Name" : "Steel Fixer","Desig_Description" : "Steel Fixer","SalaryBasis" : "Weekly","FixedSalary" : "220.00"},{"Emp_Id" : "14","Identity_No" : "","Emp_Name" : "Mani","Address" : "Madurai","Date_Of_Birth" : "","Desig_Name" : "Steel Helper","Desig_Description" : "Steel Helper","SalaryBasis" : "Weekly","FixedSalary" : "175.00"},{"Emp_Id" : "15","Identity_No" : "","Emp_Name" : "Karthik","Address" : "Madurai","Date_Of_Birth" : "","Desig_Name" : "Wood Fixer","Desig_Description" : "Wood Fixer","SalaryBasis" : "Weekly","FixedSalary" : "195.00"},{"Emp_Id" : "16","Identity_No" : "","Emp_Name" : "Bala","Address" : "Madurai","Date_Of_Birth" : "","Desig_Name" : "Wood Fixer","Desig_Description" : "Wood Fixer","SalaryBasis" : "Weekly","FixedSalary" : "185.00"},{"Emp_Id" : "17","Identity_No" : "","Emp_Name" : "Tamil arasi","Address" : "Madurai","Date_Of_Birth" : "","Desig_Name" : "Wood Helper","Desig_Description" : "Wood Helper","SalaryBasis" : "Weekly","FixedSalary" : "185.00"},{"Emp_Id" : "18","Identity_No" : "","Emp_Name" : "Perumal","Address" : "Madurai","Date_Of_Birth" : "","Desig_Name" : "Cook","Desig_Description" : "Cook","SalaryBasis" : "Weekly","FixedSalary" : "105.00"},{"Emp_Id" : "19","Identity_No" : "","Emp_Name" : "Andiappan","Address" : "Madurai","Date_Of_Birth" : "","Desig_Name" : "Watchman","Desig_Description" : "Watchman","SalaryBasis" : "Weekly","FixedSalary" : "150.00"}]} There are 22 records in this json... How to paginate this json data 5 per page using jquery? EDIT: The above image is my summary view of employee list iterated using jquery var jsonObj = JSON.parse(HfJsonValue); for (var i = jsonObj.Table.length - 1; i >= 0; i--) { var employee = jsonObj.Table[i]; $('<div class="resultsdiv"> ' + employee.Emp_Name + 'Category : ' + employee.Desig_Name + ' Salary Basis : ' + employee.SalaryBasis + 'Salary : ' + employee.FixedSalary + 'Address : ' + employee.Address + '</div>').insertAfter('#ResultsDiv'); } I get 22 records now it may grow how to paginate json date by using jquery pagination.. Any suggestion...

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Efficiency of Java "Double Brace Initialization"?

- by Jim Ferrans

In Hidden Features of Java the top answer mentions Double Brace Initialization, with a very enticing syntax: Set<String> flavors = new HashSet<String>() {{ add("vanilla"); add("strawberry"); add("chocolate"); add("butter pecan"); }}; This idiom creates an anonymous inner class with just an instance initializer in it, which "can use any [...] methods in the containing scope". Main question: Is this as inefficient as it sounds? Should its use be limited to one-off initializations? (And of course showing off!) Second question: The new HashSet must be the "this" used in the instance initializer ... can anyone shed light on the mechanism? Third question: Is this idiom too obscure to use in production code? Summary: Very, very nice answers, thanks everyone. On question (3), people felt the syntax should be clear (though I'd recommend an occasional comment, especially if your code will pass on to developers who may not be familiar with it). On question (1), The generated code should run quickly. The extra .class files do cause jar file clutter, and slow program startup slightly (thanks to coobird for measuring that). Thilo pointed out that garbage collection can be affected, and the memory cost for the extra loaded classes may be a factor in some cases. Question (2) turned out to be most interesting to me. If I understand the answers, what's happening in DBI is that the anonymous inner class extends the class of the object being constructed by the new operator, and hence has a "this" value referencing the instance being constructed. Very neat. Overall, DBI strikes me as something of an intellectual curiousity. Coobird and others point out you can achieve the same effect with Arrays.asList, varargs methods, Google Collections, and the proposed Java 7 Collection literals. Newer JVM languages like Scala, JRuby, and Groovy also offer concise notations for list construction, and interoperate well with Java. Given that DBI clutters up the classpath, slows down class loading a bit, and makes the code a tad more obscure, I'd probably shy away from it. However, I plan to spring this on a friend who's just gotten his SCJP and loves good natured jousts about Java semantics! ;-) Thanks everyone!

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WPF MVVM: Convention over Configuration for ResourceDictionary ?

- by Jeffrey Knight

Update In the wiki spirit of StackOverflow, here's an update: I spiked Joe White's IValueConverter suggestion below. It works like a charm. I've written a "quickstart" example of this that automates the mapping of ViewModels-Views using some cheap string replacement. If no View is found to represent the ViewModel, it defaults to an "Under Construction" page. I'm dubbing this approach "WPF MVVM White" since it was Joe White's idea. Here are a couple screenshots. The first image is a case of "[SomeControlName]ViewModel" has a corresponding "[SomeControlName]View", based on pure naming convention. The second is a case where the ModelView doesn't have any views to represent it. No more ResourceDictionaries with long ViewModel to View mappings. It's pure naming convention now. I'm hosting a download of the project here: http://rootsilver.com/files/Mvvm.White.Quickstart.zip I'll follow up with a longer blog post walk through. Original Post I read Josh Smith's fantastic MSDN article on WPF MVVM over the weekend. It's destined to be a cult classic. It took me a while to wrap my head around the magic of asking WPF to render the ViewModel. It's like saying "Here's a class, WPF. Go figure out which UI to use to present it." For those who missed this magic, WPF can do this by looking up the View for ModelView in the ResourceDictionary mapping and pulling out the corresponding View. (Scroll down to Figure 10 Supplying a View ). The first thing that jumps out at me immediately is that there's already a strong naming convention of: classNameView ("View" suffix) classNameViewModel ("ViewModel" suffix) My question is: Since the ResourceDictionary can be manipulated programatically, I"m wondering if anyone has managed to Regex.Replace the whole thing away, so the lookup is automatic, and any new View/ViewModels get resolved by virtue of their naming convention? [Edit] What I'm imagining is a hook/interception into ResourceDictionary. ... Also considering a method at startup that uses interop to pull out *View$ and *ViewModel$ class names to build the DataTemplate dictionary in code: //build list foreach .... String.Format("<DataTemplate DataType=\"{x:Type vm:{0} }\"><v:{1} /></DataTemplate>", ...)

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POD global object initialization

- by paercebal

I've got bitten today by a bug. The following source can be copy/pasted (and then compiled) into a main.cpp file #include <iostream> // The point of SomeGlobalObject is for its // constructor to be launched before the main // ... struct SomeGlobalObject { SomeGlobalObject() ; } ; // ... // Which explains the global object SomeGlobalObject oSomeGlobalObject ; // A POD... I was hoping it would be constructed at // compile time when using an argument list struct MyPod { short m_short ; const char * const m_string ; } ; // declaration/Initialization of a MyPod array MyPod myArrayOfPod[] = { { 1, "Hello" }, { 2, "World" }, { 3, " !" } } ; // declaration/Initialization of an array of array of void * void * myArrayOfVoid[][2] = { { (void *)1, "Hello" }, { (void *)2, "World" }, { (void *)3, " !" } } ; // constructor of the global object... Launched BEFORE main SomeGlobalObject::SomeGlobalObject() { std::cout << "myArrayOfPod[0].m_short : " << myArrayOfPod[0].m_short << std::endl ; std::cout << "myArrayOfVoid[0][0] : " << myArrayOfVoid[0][0] << std::endl ; } // main... What else ? int main(int argc, char* argv[]) { return 0 ; } MyPod being a POD, I believed there would be no constructors. Only initialization at compile time. Thus, the global object SomeGlobalObject would have no problem to use the global array of PODs upon its construction. The problem is that in real life, nothing is so simple. On Visual C++ 2008 (I did not test on other compilers), upon execution myArrayOfPodis not initialized, even ifmyArrayOfVoid` is initialized. So my questions is: Are C++ compilers not supposed to initialize global PODs (including POD structures) at compilation time ? Note that I know global variable are evil, and I know that one can't be sure of the order of creation of global variables declared in different compilation units. The problem here is really the POD C-like initialization which seems to call a constructor (the default, compiler-generated one?). And to make everyone happy: This is on debug. On release, the global array of PODs is correctly initialized.

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When is #include <new> library required in C++?

- by Czarak

Hi, According to this reference entry for operator new ( http://www.cplusplus.com/reference/std/new/operator%20new/ ) : Global dynamic storage operator functions are special in the standard library: All three versions of operator new are declared in the global namespace, not in the std namespace. The first and second versions are implicitly declared in every translation unit of a C++ program: The header does not need to be included for them to be present. This seems to me to imply that the third version of operator new (placement new) is not implicitly declared in every translation unit of a C++ program and the header <new> does need to be included for it to be present. Is that correct? If so, how is it that using both g++ and MS VC++ Express compilers it seems I can compile code using the third version of new without #include <new> in my source code? Also, the MSDN Standard C++ Library reference entry on operator new gives some example code for the three forms of operator new which contains the #include <new> statement, however the example seems to compile and run just the same for me without this include? // new_op_new.cpp // compile with: /EHsc #include<new> #include<iostream> using namespace std; class MyClass { public: MyClass( ) { cout << "Construction MyClass." << this << endl; }; ~MyClass( ) { imember = 0; cout << "Destructing MyClass." << this << endl; }; int imember; }; int main( ) { // The first form of new delete MyClass* fPtr = new MyClass; delete fPtr; // The second form of new delete char x[sizeof( MyClass )]; MyClass* fPtr2 = new( &x[0] ) MyClass; fPtr2 -> ~MyClass(); cout << "The address of x[0] is : " << ( void* )&x[0] << endl; // The third form of new delete MyClass* fPtr3 = new( nothrow ) MyClass; delete fPtr3; } Could anyone shed some light on this and when and why you might need to #include <new> - maybe some example code that will not compile without #include <new> ? Thanks.

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Dependency property does not work within a geometry in a controltemplate

- by Erik Bongers

I have a DepencencyProperty (a boolean) that works fine on an Ellipse, but not on an ArcSegment. Am I doing something that is not possible? Here's part of the xaml. Both the TemplateBindings of Origin and LargeArc do not work in the geometry. But the LargeArc DependencyProperty does work in the Ellipse, so my DependencyProperty seems to be set up correctly. <ControlTemplate TargetType="{x:Type nodes:TestCircle}"> <Canvas Background="AliceBlue"> <Ellipse Height="10" Width="10" Fill="Yellow" Visibility="{TemplateBinding LargeArc, Converter={StaticResource BoolToVisConverter}}"/> <Path Canvas.Left="0" Canvas.Top="0" Stroke="Black" StrokeThickness="3"> <Path.Data> <GeometryGroup> <PathGeometry> <PathFigure IsClosed="True" StartPoint="{TemplateBinding Origin}"> <LineSegment Point="150,100" /> <ArcSegment Point="140,150" IsLargeArc="{TemplateBinding LargeArc}" Size="50,50" SweepDirection="Clockwise"/> </PathFigure> </PathGeometry> </GeometryGroup> </Path.Data> </Path> </Canvas> </ControlTemplate> What I'm trying to build is a (sort of) pie-shaped usercontrol where the shape of the Pie is defined by DependencyProperties and the actual graphics used are in a template, so they can be replaced or customized. In other words: I would like the code-behind to be visual-free (which, I assume, is good separation). SOLUTION--------------------------(I'm not allowed to answer my own questions yet) I found the answer myself, and this can be useful for others encountering the same issue. This is why the TemplateBinding on the Geometry failed: A TemplateBinding will only work when binding a DependencyProperty to another DependencyProperty. Following article set me on the right track: http://blogs.msdn.com/b/liviuc/archive/2009/12/14/wpf-templatebinding-vs-relativesource-templatedparent.aspx The ArcSegment properties are no DependencyProperties. Thus, the solution to the above problem is to replace <ArcSegment Point="140,150" IsLargeArc="{TemplateBinding LargeArc}" with <ArcSegment Point="140,150" IsLargeArc="{Binding RelativeSource={RelativeSource TemplatedParent}, Path=LargeArc}" Colin, your working example where an 'ordinary' binding was used in the geometry set me on the right track. BTW, love the infographics and the construction of your UserControl in your blogpost. And, hey, that quick tip on code snippets, and especially on that DP attribute and the separation of those DPs into a partial class file is pure gold!

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question about book example - Java Concurrency in Practice, Listing 4.12

- by mike

Hi, I am working through an example in Java Concurrency in Practice and am not understanding why a concurrent-safe container is necessary in the following code. I'm not seeing how the container "locations" 's state could be modified after construction; so since it is published through an 'unmodifiableMap' wrapper, it appears to me that an ordinary HashMap would suffice. EG, it is accessed concurrently, but the state of the map is only accessed by readers, no writers. The value fields in the map are syncronized via delegation to the 'SafePoint' class, so while the points are mutable, the keys for the hash, and their associated values (references to SafePoint instances) in the map never change. I think my confusion is based on what precisely the state of the collection is in the problem. Thanks!! -Mike Listing 4.12, Java Concurrency in Practice, (this listing available as .java here, and also in chapter form via google) /////////////begin code @ThreadSafe public class PublishingVehicleTracker { private final Map<String, SafePoint> locations; private final Map<String, SafePoint> unmodifiableMap; public PublishingVehicleTracker( Map<String, SafePoint> locations) { this.locations = new ConcurrentHashMap<String, SafePoint>(locations); this.unmodifiableMap = Collections.unmodifiableMap(this.locations); } public Map<String, SafePoint> getLocations() { return unmodifiableMap; } public SafePoint getLocation(String id) { return locations.get(id); } public void setLocation(String id, int x, int y) { if (!locations.containsKey(id)) throw new IllegalArgumentException( "invalid vehicle name: " + id); locations.get(id).set(x, y); } } // monitor protected helper-class @ThreadSafe public class SafePoint { @GuardedBy("this") private int x, y; private SafePoint(int[] a) { this(a[0], a[1]); } public SafePoint(SafePoint p) { this(p.get()); } public SafePoint(int x, int y) { this.x = x; this.y = y; } public synchronized int[] get() { return new int[] { x, y }; } public synchronized void set(int x, int y) { this.x = x; this.y = y; } } ///////////end code

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Good style for handling constructor failure of critical object

- by mtlphil

I'm trying to decide between two ways of instantiating an object & handling any constructor exceptions for an object that is critical to my program, i.e. if construction fails the program can't continue. I have a class SimpleMIDIOut that wraps basic Win32 MIDI functions. It will open a MIDI device in the constructor and close it in the destructor. It will throw an exception inherited from std::exception in the constructor if the MIDI device cannot be opened. Which of the following ways of catching constructor exceptions for this object would be more in line with C++ best practices Method 1 - Stack allocated object, only in scope inside try block #include <iostream> #include "simplemidiout.h" int main() { try { SimpleMIDIOut myOut; //constructor will throw if MIDI device cannot be opened myOut.PlayNote(60,100); //..... //myOut goes out of scope outside this block //so basically the whole program has to be inside //this block. //On the plus side, it's on the stack so //destructor that handles object cleanup //is called automatically, more inline with RAII idiom? } catch(const std::exception& e) { std::cout << e.what() << std::endl; std::cin.ignore(); return 1; } std::cin.ignore(); return 0; } Method 2 - Pointer to object, heap allocated, nicer structured code? #include <iostream> #include "simplemidiout.h" int main() { SimpleMIDIOut *myOut; try { myOut = new SimpleMIDIOut(); } catch(const std::exception& e) { std::cout << e.what() << std::endl; delete myOut; return 1; } myOut->PlayNote(60,100); std::cin.ignore(); delete myOut; return 0; } I like the look of the code in Method 2 better, don't have to jam my whole program into a try block, but Method 1 creates the object on the stack so C++ manages the object's life time, which is more in tune with RAII philosophy isn't it? I'm still a novice at this so any feedback on the above is much appreciated. If there's an even better way to check for/handle constructor failure in a siatuation like this please let me know.

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How does the event dispatch thread work?

- by Roman

With the help of people on stackoverflow I was able to get the following working code of the simples GUI countdown (it just displays a window counting down seconds). My main problem with this code is the invokeLater stuff. As far as I understand the invokeLater send a task to the event dispatching thread (EDT) and then the EDT execute this task whenever it "can" (whatever it means). Is it right? To my understanding the code works like that: In the main method we use invokeLater to show the window (showGUI method). In other words, the code displaying the window will be executed in the EDT. In the main method we also start the counter and the counter (by construction) is executed in another thread (so it is not in the event dispatching thread). Right? The counter is executed in a separate thread and periodically it calls updateGUI. The updateGUI is supposed to update GUI. And GUI is working in the EDT. So, updateGUI should also be executed in the EDT. It is why the code for the updateGUI is inclosed in the invokeLater. Is it right? What is not clear to me is why we call the counter from the EDT. Anyway it is not executed in the EDT. It starts immediately a new thread and the counter is executed there. So, why we cannot call the counter in the main method after the invokeLater block? import javax.swing.JFrame; import javax.swing.JLabel; import javax.swing.SwingUtilities; public class CountdownNew { static JLabel label; // Method which defines the appearance of the window. public static void showGUI() { JFrame frame = new JFrame("Simple Countdown"); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); label = new JLabel("Some Text"); frame.add(label); frame.pack(); frame.setVisible(true); } // Define a new thread in which the countdown is counting down. public static Thread counter = new Thread() { public void run() { for (int i=10; i>0; i=i-1) { updateGUI(i,label); try {Thread.sleep(1000);} catch(InterruptedException e) {}; } } }; // A method which updates GUI (sets a new value of JLabel). private static void updateGUI(final int i, final JLabel label) { SwingUtilities.invokeLater( new Runnable() { public void run() { label.setText("You have " + i + " seconds."); } } ); } public static void main(String[] args) { SwingUtilities.invokeLater(new Runnable() { public void run() { showGUI(); counter.start(); } }); } }

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Simplest way to flatten document to a view in RavenDB

- by degorolls

Given the following classes: public class Lookup { public string Code { get; set; } public string Name { get; set; } } public class DocA { public string Id { get; set; } public string Name { get; set; } public Lookup Currency { get; set; } } public class ViewA // Simply a flattened version of the doc { public string Id { get; set; } public string Name { get; set; } public string CurrencyName { get; set; } // View just gets the name of the currency } I can create an index that allows client to query the view as follows: public class A_View : AbstractIndexCreationTask<DocA, ViewA> { public A_View() { Map = docs => from doc in docs select new ViewA { Id = doc.Id, Name = doc.Name, CurrencyName = doc.Currency.Name }; Reduce = results => from result in results group on new ViewA { Id = result.Id, Name = result.Name, CurrencyName = result.CurrencyName } into g select new ViewA { Id = g.Key.Id, Name = g.Key.Name, CurrencyName = g.Key.CurrencyName }; } } This certainly works and produces the desired result of a view with the data transformed to the structure required at the client application. However, it is unworkably verbose, will be a maintenance nightmare and is probably fairly inefficient with all the redundant object construction. Is there a simpler way of creating an index with the required structure (ViewA) given a collection of documents (DocA)? FURTHER INFORMATION The issue appears to be that in order to have the index hold the data in the transformed structure (ViewA), we have to do a Reduce. It appears that a Reduce must have both a GROUP ON and a SELECT in order to work as expected so the following are not valid: INVALID REDUCE CLAUSE 1: Reduce = results => from result in results group on new ViewA { Id = result.Id, Name = result.Name, CurrencyName = result.CurrencyName } into g select g.Key; This produces: System.InvalidOperationException: Variable initializer select must have a lambda expression with an object create expression Clearly we need to have the 'select new'. INVALID REDUCE CLAUSE 2: Reduce = results => from result in results select new ViewA { Id = result.Id, Name = result.Name, CurrencyName = result.CurrencyName }; This prduces: System.InvalidCastException: Unable to cast object of type 'ICSharpCode.NRefactory.Ast.IdentifierExpression' to type 'ICSharpCode.NRefactory.Ast.InvocationExpression'. Clearly, we also need to have the 'group on new'. Thanks for any assistance you can provide. (Note: removing the type (ViewA) from the constructor calls has no effect on the above)

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Implementing Skip List in C++

- by trikker

[SOLVED] So I decided to try and create a sorted doubly linked skip list... I'm pretty sure I have a good grasp of how it works. When you insert x the program searches the base list for the appropriate place to put x (since it is sorted), (conceptually) flips a coin, and if the "coin" lands on a then that element is added to the list above it(or a new list is created with element in it), linked to the element below it, and the coin is flipped again, etc. If the "coin" lands on b at anytime then the insertion is over. You must also have a -infinite stored in every list as the starting point so that it isn't possible to insert a value that is less than the starting point (meaning that it could never be found.) To search for x, you start at the "top-left" (highest list lowest value) and "move right" to the next element. If the value is less than x than you continue to the next element, etc. until you have "gone too far" and the value is greater than x. In this case you go back to the last element and move down a level, continuing this chain until you either find x or x is never found. To delete x you simply search x and delete it every time it comes up in the lists. For now, I'm simply going to make a skip list that stores numbers. I don't think there is anything in the STL that can assist me, so I will need to create a class List that holds an integer value and has member functions, search, delete, and insert. The problem I'm having is dealing with links. I'm pretty sure I could create a class to handle the "horizontal" links with a pointer to the previous element and the element in front, but I'm not sure how to deal with the "vertical" links (point to corresponding element in other list?) If any of my logic is flawed please tell me, but my main questions are: How to deal with vertical links and whether my link idea is correct Now that I read my class List idea I'm thinking that a List should hold a vector of integers rather than a single integer. In fact I'm pretty positive, but would just like some validation. I'm assuming the coin flip would simply call int function where rand()%2 returns a value of 0 or 1 and if it's 0 then a the value "levels up" and if it's 0 then the insert is over. Is this incorrect? How to store a value similar to -infinite? Edit: I've started writing some code and am considering how to handle the List constructor....I'm guessing that on its construction, the "-infinite" value should be stored in the vectorname[0] element and I can just call insert on it after its creation to put the x in the appropriate place.

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Implementing a scalable and high-performing web app

- by Christopher McCann

I have asked a few questions on here before about various things relating to this but this is more of a consolidation question as I would like to check I have got the gist of everything. I am in the middle of developing a social media web app and although I have a lot of experience coding in Java and in PHP I am trying things a bit different this time. I have modularised each component of the application. So for example one component of the application allows users to private message each other and I have split this off into its own private messaging service. I have also created a user data service the purpose of which is to return data about the user for example their name, address, age etc etc from the database. Their is also another service, the friends service, which will work off the neo4j database to create a social graph. My reason for doing all this is to allow me up to update seperate modules when I need to - so while they mostly all run off MySQL right now I could move one to Cassandra later if I thought it approriate. The actual code of the web app is really just used for the final construction. The modules behind it dont really follow any strict REST or SOAP protocol. Basically each method on our API is turned into a PHP procedural script. This then may make calls to other back-end code which tends to be OO. The web app makes CURL requests to these pages and POSTs data to them or GETs data from them. These pages then return JSON where data is required. I'm still a little mixed up about how I actually identify which user is logged in at that moment. Do I just use sessions for that? Like if we called the get-messages.php script which equates to the getMessages() method for that user - returning all the private messages for that user - how would the back-end code know which user it is as posting the users ID to the script would not be secure. Anyone could do that and get all the messages. So I thought I would use sessions for it. Am I correct on this? Can anyone spot any other problems with what I am doing here? Thanks

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How to cache queries in EJB and return result efficient (performance POV)

- by Maxym

I use JBoss EJB 3.0 implementation (JBoss 4.2.3 server) At the beginning I created native query all the time using construction like Query query = entityManager.createNativeQuery("select * from _table_"); Of couse it is not that efficient, I performed some tests and found out that it really takes a lot of time... Then I found a better way to deal with it, to use annotation to define native queries: @NamedNativeQuery( name = "fetchData", value = "select * from _table_", resultClass=Entity.class ) and then just use it Query query = entityManager.createNamedQuery("fetchData"); the performance of code line above is two times better than where I started from, but still not that good as I expected... then I found that I can switch to Hibernate annotation for NamedNativeQuery (anyway, JBoss's implementation of EJB is based on Hibernate), and add one more thing: @NamedNativeQuery( name = "fetchData2", value = "select * from _table_", resultClass=Entity.class, readOnly=true) readOnly - marks whether the results are fetched in read-only mode or not. It sounds good, because at least in this case of mine I don't need to update data, I wanna just fetch it for report. When I started server to measure performance I noticed that query without readOnly=true (by default it is false) returns result with each iteration better and better, and at the same time another one (fetchData2) works like "stable" and with time difference between them is shorter and shorter, and after 5 iterations speed of both was almost the same... The questions are: 1) is there any other way to speed query using up? Seems that named queries should be prepared once, but I can't say it... In fact if to create query once and then just use it it would be better from performance point of view, but it is problematic to cache this object, because after creating query I can set parameters (when I use ":variable" in query), and it changes query object (isn't it?). well, is here any way to cache them? Or named query is the best option I can use? 2) any other approaches how to make results retrieveng faster. I mean, for instance I don't need those Entities to be attached, I won't update them, all I need is just fetch collection of data. Maybe readOnly is the only available way, so I can't speed it up, but who knows :) P.S. I don't ask about DB performance, all I need now is how not to create query all the time, so use it efficient, and to "allow" EJB to do less job with the same result concerning data returning.

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Supporting multiple instances of a plugin DLL with global data

- by Bruno De Fraine

Context: I converted a legacy standalone engine into a plugin component for a composition tool. Technically, this means that I compiled the engine code base to a C DLL which I invoke from a .NET wrapper using P/Invoke; the wrapper implements an interface defined by the composition tool. This works quite well, but now I receive the request to load multiple instances of the engine, for different projects. Since the engine keeps the project data in a set of global variables, and since the DLL with the engine code base is loaded only once, loading multiple projects means that the project data is overwritten. I can see a number of solutions, but they all have some disadvantages: You can create multiple DLLs with the same code, which are seen as different DLLs by Windows, so their code is not shared. Probably this already works if you have multiple copies of the engine DLL with different names. However, the engine is invoked from the wrapper using DllImport attributes and I think the name of the engine DLL needs to be known when compiling the wrapper. Obviously, if I have to compile different versions of the wrapper for each project, this is quite cumbersome. The engine could run as a separate process. This means that the wrapper would launch a separate process for the engine when it loads a project, and it would use some form of IPC to communicate with this process. While this is a relatively clean solution, it requires some effort to get working, I don't now which IPC technology would be best to set-up this kind of construction. There may also be a significant overhead of the communication: the engine needs to frequently exchange arrays of floating-point numbers. The engine could be adapted to support multiple projects. This means that the global variables should be put into a project structure, and every reference to the globals should be converted to a corresponding reference that is relative to a particular project. There are about 20-30 global variables, but as you can imagine, these global variables are referenced from all over the code base, so this conversion would need to be done in some automatic manner. A related problem is that you should be able to reference the "current" project structure in all places, but passing this along as an extra argument in each and every function signature is also cumbersome. Does there exist a technique (in C) to consider the current call stack and find the nearest enclosing instance of a relevant data value there? Can the stackoverflow community give some advice on these (or other) solutions?

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WinForm-style Invoke() in unmanaged C++

- by Matt Green

I've been playing with a DataBus-type design for a hobby project, and I ran into an issue. Back-end components need to notify the UI that something has happened. My implementation of the bus delivers the messages synchronously with respect to the sender. In other words, when you call Send(), the method blocks until all the handlers have called. (This allows callers to use stack memory management for event objects.) However, consider the case where an event handler updates the GUI in response to an event. If the handler is called, and the message sender lives on another thread, then the handler cannot update the GUI due to Win32's GUI elements having thread affinity. More dynamic platforms such as .NET allow you to handle this by calling a special Invoke() method to move the method call (and the arguments) to the UI thread. I'm guessing they use the .NET parking window or the like for these sorts of things. A morbid curiosity was born: can we do this in C++, even if we limit the scope of the problem? Can we make it nicer than existing solutions? I know Qt does something similar with the moveToThread() function. By nicer, I'll mention that I'm specifically trying to avoid code of the following form: if(! this->IsUIThread()) { Invoke(MainWindowPresenter::OnTracksAdded, e); return; } being at the top of every UI method. This dance was common in WinForms when dealing with this issue. I think this sort of concern should be isolated from the domain-specific code and a wrapper object made to deal with it. My implementation consists of: DeferredFunction - functor that stores the target method in a FastDelegate, and deep copies the single event argument. This is the object that is sent across thread boundaries. UIEventHandler - responsible for dispatching a single event from the bus. When the Execute() method is called, it checks the thread ID. If it does not match the UI thread ID (set at construction time), a DeferredFunction is allocated on the heap with the instance, method, and event argument. A pointer to it is sent to the UI thread via PostThreadMessage(). Finally, a hook function for the thread's message pump is used to call the DeferredFunction and de-allocate it. Alternatively, I can use a message loop filter, since my UI framework (WTL) supports them. Ultimately, is this a good idea? The whole message hooking thing makes me leery. The intent is certainly noble, but are there are any pitfalls I should know about? Or is there an easier way to do this?

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PyGTK: Radiobuttons are still displayed after removal

- by canavanin

Hi everyone! I am using PyGTK and the gtk.assistant. On one page I would like to display two radiobuttons in case the user selected a certain option on a previous page. The labels of the buttons - and whether the buttons are to be present at all - are to depend entirely on that earlier selection. Furthermore, if the user goes back and changes that selection, the page containing the radiobuttons is to be updated accordingly. I have got as far as having the radiobuttons displayed when necessary, and with the correct labels. The trouble is that if I go back and change the determining selection, or if I move one page further than the 'radiobutton page' and then move back, the buttons are not only not removed (in case that would have been required), their number has also doubled. To show you what I'm doing, here's part of my code (I've left out bits that do unrelated things, that's why the function name doesn't fit). The function is called when the "prepare" signal is emitted prior to construction of the 'radiobutten page'. def make_class_skills_treestore(self): print self.trained_by_default_hbox.get_children() # PRINT 1 for child in self.trained_by_default_hbox.get_children(): if type(child) == gtk.RadioButton: self.trained_by_default_hbox.remove(child) #child.destroy() # <-- removed the labels, but not the buttons print self.trained_by_default_hbox.get_children() # PRINT 2 class_skills = self.data.data['classes'][selected_class].class_skills.values() default_trained_count = (class_skills.count([True, True]) , class_skills.count([True, False])) num_default_trained_skills = default_trained_count[1] / 2 # you have to pick one of a pair --> don't # count each as trained by default for i in range(default_trained_count[0]): # those are trained by default --> no choice num_default_trained_skills +=1 selected_class = self.get_classes_key_from_class_selection() if default_trained_count[1]: for skill in self.data.data['classes'][selected_class].class_skills.keys(): if self.data.data['classes'][selected_class].class_skills[skill] == [ True, False ] and not self.default_radio: self.default_radio.append(gtk.RadioButton(group=None, label=skill)) elif self.data.data['classes'][selected_class].class_skills[skill] == [ True, False ] and self.default_radio: self.default_radio.append(gtk.RadioButton(group=self.default_radio[0], label=skill)) if self.default_radio: for radio in self.default_radio: self.trained_by_default_hbox.add(radio) self.trained_by_default_hbox.show_all() self.trained_by_default_hbox and self.trained_by_default_label, as well as self.default_radio stem from the above function's class. I have two print statements (PRINT 1 and PRINT 2) in there for debugging. Here's what they give me: PRINT 1: [<gtk.Label object at 0x8fc4c84 (GtkLabel at 0x90a2f20)>, <gtk.RadioButton object at 0x8fc4d4c (GtkRadioButton at 0x90e4018)>, <gtk.RadioButton object at 0x8fc4cac (GtkRadioButton at 0x90ceec0)>] PRINT 2: [<gtk.Label object at 0x8fc4c84 (GtkLabel at 0x90a2f20)>] So the buttons have indeed been removed, yet they still show up on the page. I know the code requires some refactoring, but first I'd like to get it to work at all... If someone could help me out that would be great! Thanks a lot in advance for your replies - any kind of help is highly appreciated.

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c++ std::ostringstream vs std::string::append

- by NickSoft

In all examples that use some kind of buffering I see they use stream instead of string. How is std::ostringstream and << operator different than using string.append. Which one is faster and which one uses less resourses (memory). One difference I know is that you can output different types into output stream (like integer) rather than the limited types that string::append accepts. Here is an example: std::ostringstream os; os << "Content-Type: " << contentType << ";charset=" << charset << "\r\n"; std::string header = os.str(); vs std::string header("Content-Type: "); header.append(contentType); header.append(";charset="); header.append(charset); header.append("\r\n"); Obviously using stream is shorter, but I think append returns reference to the string so it can be written like this: std::string header("Content-Type: "); header.append(contentType) .append(";charset=") .append(charset) .append("\r\n"); And with output stream you can do: std::string content; ... os << "Content-Length: " << content.length() << "\r\n"; But what about memory usage and speed? Especially when used in a big loop. Update: To be more clear the question is: Which one should I use and why? Is there situations when one is preferred or the other? For performance and memory ... well I think benchmark is the only way since every implementation could be different. Update 2: Well I don't get clear idea what should I use from the answers which means that any of them will do the job, plus vector. Cubbi did nice benchmark with the addition of Dietmar Kühl that the biggest difference is construction of those objects. If you are looking for an answer you should check that too. I'll wait a bit more for other answers (look previous update) and if I don't get one I think I'll accept Tolga's answer because his suggestion to use vector is already done before which means vector should be less resource hungry.

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Is it a good or bad practice to call instance methods from a java constructor?

- by Steve

There are several different ways I can initialize complex objects (with injected dependencies and required set-up of injected members), are all seem reasonable, but have various advantages and disadvantages. I'll give a concrete example: final class MyClass { private final Dependency dependency; @Inject public MyClass(Dependency dependency) { this.dependency = dependency; dependency.addHandler(new Handler() { @Override void handle(int foo) { MyClass.this.doSomething(foo); } }); doSomething(0); } private void doSomething(int foo) { dependency.doSomethingElse(foo+1); } } As you can see, the constructor does 3 things, including calling an instance method. I've been told that calling instance methods from a constructor is unsafe because it circumvents the compiler's checks for uninitialized members. I.e. I could have called doSomething(0) before setting this.dependency, which would have compiled but not worked. What is the best way to refactor this? Make doSomething static and pass in the dependency explicitly? In my actual case I have three instance methods and three member fields that all depend on one another, so this seems like a lot of extra boilerplate to make all three of these static. Move the addHandler and doSomething into an @Inject public void init() method. While use with Guice will be transparent, it requires any manual construction to be sure to call init() or else the object won't be fully-functional if someone forgets. Also, this exposes more of the API, both of which seem like bad ideas. Wrap a nested class to keep the dependency to make sure it behaves properly without exposing additional API:class DependencyManager { private final Dependency dependency; public DependecyManager(Dependency dependency) { ... } public doSomething(int foo) { ... } } @Inject public MyClass(Dependency dependency) { DependencyManager manager = new DependencyManager(dependency); manager.doSomething(0); } This pulls instance methods out of all constructors, but generates an extra layer of classes, and when I already had inner and anonymous classes (e.g. that handler) it can become confusing - when I tried this I was told to move the DependencyManager to a separate file, which is also distasteful because it's now multiple files to do a single thing. So what is the preferred way to deal with this sort of situation?

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Why does OpenGL's glDrawArrays() fail with GL_INVALID_OPERATION under Core Profile 3.2, but not 3.3 or 4.2?

- by metaleap

I have OpenGL rendering code calling glDrawArrays that works flawlessly when the OpenGL context is (automatically / implicitly obtained) 4.2 but fails consistently (GL_INVALID_OPERATION) with an explicitly requested OpenGL core context 3.2. (Shaders are always set to #version 150 in both cases but that's beside the point here I suspect.) According to specs, there are only two instances when glDrawArrays() fails with GL_INVALID_OPERATION: "if a non-zero buffer object name is bound to an enabled array and the buffer object's data store is currently mapped" -- I'm not doing any buffer mapping at this point "if a geometry shader is active and mode? is incompatible with [...]" -- nope, no geometry shaders as of now. Furthermore: I have verified & double-checked that it's only the glDrawArrays() calls failing. Also double-checked that all arguments passed to glDrawArrays() are identical under both GL versions, buffer bindings too. This happens across 3 different nvidia GPUs and 2 different OSes (Win7 and OSX, both 64-bit -- of course, in OSX we have only the 3.2 context, no 4.2 anyway). It does not happen with an integrated "Intel HD" GPU but for that one, I only get an automatic implicit 3.3 context (trying to explicitly force a 3.2 core profile with this GPU via GLFW here fails the window creation but that's an entirely different issue...) For what it's worth, here's the relevant routine excerpted from the render loop, in Golang: func (me *TMesh) render () { curMesh = me curTechnique.OnRenderMesh() gl.BindBuffer(gl.ARRAY_BUFFER, me.glVertBuf) if me.glElemBuf > 0 { gl.BindBuffer(gl.ELEMENT_ARRAY_BUFFER, me.glElemBuf) gl.VertexAttribPointer(curProg.AttrLocs["aPos"], 3, gl.FLOAT, gl.FALSE, 0, gl.Pointer(nil)) gl.DrawElements(me.glMode, me.glNumIndices, gl.UNSIGNED_INT, gl.Pointer(nil)) gl.BindBuffer(gl.ELEMENT_ARRAY_BUFFER, 0) } else { gl.VertexAttribPointer(curProg.AttrLocs["aPos"], 3, gl.FLOAT, gl.FALSE, 0, gl.Pointer(nil)) /* BOOM! */ gl.DrawArrays(me.glMode, 0, me.glNumVerts) } gl.BindBuffer(gl.ARRAY_BUFFER, 0) } So of course this is part of a bigger render-loop, though the whole "*TMesh" construction for now is just two instances, one a simple cube and the other a simple pyramid. What matters is that the entire drawing loop works flawlessly with no errors reported when GL is queried for errors under both 3.3 and 4.2, yet on 3 nvidia GPUs with an explicit 3.2 core profile fails with an error code that according to spec is only invoked in two specific situations, none of which as far as I can tell apply here. What could be wrong here? Have you ever run into this? Any ideas what I have been missing?

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best alternative to in-definition initialization of static class members? (for SVN keywords)

- by Jeff

I'm storing expanded SVN keyword literals for .cpp files in 'static char const *const' class members and want to store the .h descriptions as similarly as possible. In short, I need to guarantee single instantiation of a static member (presumably in a .cpp file) to an auto-generated non-integer literal living in a potentially shared .h file. Unfortunately the language makes no attempt to resolve multiple instantiations resulting from assignments made outside class definitions and explicitly forbids non-integer inits inside class definitions. My best attempt (using static-wrapping internal classes) is not too dirty, but I'd really like to do better. Does anyone have a way to template the wrapper below or have an altogether superior approach? // Foo.h: class with .h/.cpp SVN info stored and logged statically class Foo { static Logger const verLog; struct hInfoWrap; public: static hInfoWrap const hInfo; static char const *const cInfo; }; // Would like to eliminate this per-class boilerplate. struct Foo::hInfoWrap { hInfoWrapper() : text("$Id$") { } char const *const text; }; ... // Foo.cpp: static inits called here Foo::hInfoWrap const Foo::hInfo; char const *const Foo::cInfo = "$Id$"; Logger const Foo::verLog(Foo::cInfo, Foo::hInfo.text); ... // Helper.h: output on construction, with no subsequent activity or stored fields class Logger { Logger(char const *info1, char const *info2) { cout << info0 << endl << info1 << endl; } }; Is there a way to get around the static linkage address issue for templating the hInfoWrap class on string literals? Extern char pointers assigned outside class definitions are linguistically valid but fail in essentially the same manner as direct member initializations. I get why the language shirks the whole resolution issue, but it'd be very convenient if an inverted extern member qualifier were provided, where the definition code was visible in class definitions to any caller but only actually invoked at the point of a single special declaration elsewhere. Anyway, I digress. What's the best solution for the language we've got, template or otherwise? Thanks!

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