name 'App' does not exist in the current context.
How that possible?
Have to note my initialization code is different than MainPage() type, as I converted SketchFlow app into production Silverlight. They instruct you to do init code via System.Windows.Controls.Frame():
private void Application_Startup(object sender, StartupEventArgs e)
{
this.RootVisual = new System.Windows.Controls.Frame() { Source = new Uri("/MyAppScreen.xaml", UriKind.Relative) };
}
public static string ValueFromHome =
"A Value on Home page";
the goal was to set up public var inside App object so I can access it from various screens down the road
Accessing Resource data requires calling App object I believe as in below, is that correct? so this won't help me
string color = App.Current.Resources["customColor"].ToString();
If you are just storing strings, look into using Resource files. Then they can be translated if that ever becomes necessary.
EDIT (to explain the resource file usage): To access the resource, first create a .resx file in your project (let's say you name it MainResource.resx), change the access modifier drop down to public, add your string with Name: ValueFromHome and Value: "A Value on Home page".
Then you can get the value by adding a using to the namespace of the resource if needed and calling it directly like so:
string value = MainResource.ValueFromHome;
I'd be wary of static variables hanging around. Maybe you could use a MainViewModel to store that value. If you really need a static variable create a new static class in your project and put your ValueFromHome property in that class. The App probably isn't available since it is a Silverlight construct and not made to be available to all areas.
Related
I am very new to WPF and MVVM Pattern. I even have no experience on windows.
I have Created Simple login window
_ Login.xaml, LoginViewModel.cs
_ Dashboard.xaml, DashboardViewModel.cs
After Login Successfully - ( In Login time we will select Language also )
I am Displaying Username & Selected Language in Dashboard window
I wrote code like this:
public partial class App : Application
{
protected override void OnStartup(StartupEventArgs e)
{
base.OnStartup(e);
try
{
var login = new Login();
var loginVM = new LoginViewModel();
Dashboard main = null;
loginVM.LoginCompleted += (sender, args) =>
{
DashboardViewModel dvModel = new DashboardViewModel(loginVM);
main = new Dashboard();
main.DataContext = dvModel;
main.ShowDialog();
login.Hide();
};
login.DataContext = loginVM;
login.ShowDialog();
}
catch (Exception ex)
{
throw ex;
}
}
In Dashboard Window it is displaying username and Language successfully.
But my problem is those two (Username & Language) properties I want to use in dashboard codebehind for update the layout based on language & other xaml files or other viewmodels . How to do that one ?
Technically I want to use Loginviewmodel object in all viewmodels.
Based on Selected Language I want to update Layout.
Note: Is this login approach good ? Is there any alternative for Globalization in MVVM pattern ?
Using a ViewModel for login is perfectly valid. I would perhaps create a token in your loginVM to pass around the system, depending on your needs. That token should be passed into the constructors of your other viewmodels from your main view model (DashboardViewModel?). This can be resolved using any decent IoC container.
For globalization/localization, I would use resources (in satellite assemblies). We've experimented with various things, and found that we didn't like the WPF UUIDs added everywhere when using LocBaml. And storing translation is a database quickly became a performance hog (even when loading in bulk). This does require you to find your labels etc. to a resource manager, but in my opinion, it is worth it.
Take a look at this article, for a nice extension, that enables you to simply write:
<TextBlock Text="{Resx MyText}"/>
And it will be translated using resource files.
An alterative approach is to simply store the Username and Language is a static property. I know most people don't like globals, but something like this is in nature very global, and you will still be able to inject it in if you so desire. The downside of this approach is that your unit tests would have to setup this static variable first.
EDIT An example of the static approach:
public static class RuntimeInfo {
public static string UserName { get; set; }
public static CultureInfo UserCulture { get; set; }
}
In your loginVM, simply store the necessary values in a static class. This can be accessed anywhere needed. This is not as 'correct' as the previous approach, but it can be more pragmatic than having to pass the username into every single ViewModel in your application.
I still recommend injection through an IoC container though.
I am trying to make Jeff's testing program, written in Silverlight 2 (http://www.jeff.wilcox.name/2008/03/silverlight2-unit-testing/), work using Silverlight 4 and VS2010 and I get a NullReferenceException at this line:
chatSession.ConnectWithRemoteUser("ScottGu");
Any ideas why? Here's code:
public Page()
{
// commented out because it doesn't exist in the current context
// according to the compiler
// InitializeComponent();
// Retrieve ChatSession instance from XAML resource declaration
chatSession = new ChatSession();
chatSession = (ChatSession)Resources["ChatSessionDS"];
// Connect with Chat Server to chat with "ScottGu"
chatSession.ConnectWithRemoteUser("ScottGu");
}
First, if you had to comment out InitializeComponent(), I Feel bad about your application: InitializeComponent is generated by the VS tools when the XAML file of your page is parsed.
If it doesn't exist, it probably means that the class declared in the xaml file is different from the one in your c# file (different name or different namespace) Otherwise, maybe the XAML file action type in the VS property tab isn't set to "page".
second:
chatSession = new ChatSession();
chatSession = (ChatSession)Resources["ChatSessionDS"];
this looks strange.you create a new ChatSession, then replace it by an object saved in the page resources. Why do you create it firstplace if you put the instance out of scope at the next line?
i have 2 projects in my solution (main is A.WPF and secondary is B.WPF)
when i'm trying to access variables inside my App.xaml.cs in B.WPF:
filename = ((App)Application.Current).ErrorLogFileName;
i get the following error:
Unable to cast object of type 'A.App' to type 'B.App'.
i also tried the following:
filename = ((B.App)Application.Current).ErrorLogFileName;
but still the same error...
the definition in B.App is:
private string _errorLogFileName = "error log.xml";
public string ErrorLogFileName
{
get { return _errorLogFileName; }
}
please assist...
Looks like you need to do:
filename = ((A.App)Application.Current).ErrorLogFileName;
The error is saying the type is A.App, yet in both cases you are trying to cast to B.App.
There can only be one current application also.
Application.Current refers to the current application. The only way to be allowed to cast the current App to another App-type is when the other App-type is a base class of the current App-type.
Are A.App and B.App siblings or is B.App a base class of A.App?
If you don't want B to have a reference to A (or can't as you want A to reference B and that would cause a circular reference), then you need a common type defined in a third assembly that both A and B reference. In our implementation we tend to have a ConfigurationData type that is in a separate project referenced by both Wpf projects, e.g.
public static class ConfigurationData
{
private static string _errorLogFileName = "error log.xml";
public string ErrorLogFileName
{
get { return _errorLogFileName; }
}
}
Another approach would be to define an Interface for your ErrorLogFileName property in a 3rd assembly that both A and B reference, and then implement that interface on your Wpf Application class - A and B would then both be able to cast to that type. If you wanted your A project to set the values on that at runtime, you could make the ErrorLogFileName a read-write property instead and initialize it in your application startup.
I personally prefer using a separate ConfigurationData type from the Wpf app object for this kind of stuff (ErrorLogFileName etc.) as it can then also be used for code that might execute in a unit test and therefore might not be running under a Wpf application - it also avoids having to do casts all over the place (ConfigurationData.ErrorLogFileName instead of ((IAppConfigurationData)Application.Current).ErrorLogFileName.
BTW, if you have an Application object in both assemblies it sounds like you might have both assemblies configured to build as Output type: Windows Application in your project properties. You should only really have one assembly that is configured as the Windows Application and the rest should be Class Library to avoid confusing numbers of Application classes being generated - only the one in the main EXE (and it's related resources) will get created at runtime.
I have few public properties in App.xaml.cs which is in project A and I want to refer them in my project B. However my project A has a reference to project B, so I cannot add again the reference of project A in project B otherwise it will result in cyclic error. So how can I refer those properties in my class library? I don't want to use reflection :).
As a workaround I have stored those properties in one class in project B (so it can be referred in project A as well as project B) and made those properties to be static and all works fine. However I am still curious to know what if I had stored them in App.xaml.cs? Any options available?
Thanks in advance :)
The App class should expose things that are only relevant to the application project. As soon as you realised that you wanted these things accessable in B.dll they became relevant to more than just the application project and therefore no longer belong in the application project.
Adding a class to B.dll that carries these things as static properties could be a reasonable approach. Another common pattern is to have a single Current static property.
public MyClass
{
private static MyClass _current = new MyClass();
public static MyClass Current { get { return _current; } }
public string SomeInstanceValue { get; set; }
}
Both A and B would access things using the pattern var x = MyClass.Current.SomeInstanceValue. The advantage of this approach is that it allows the Current property getter to determine if a "current" instance is available or not.
You might also want to review the documentation on ApplicationLifeTimeObjects.
When A and B both need something, maybe you should put them in a C project (C as in Common) and then refer to C from both A and B.
I have a Silverlight application which has two different XAPs - an InitialXAP which is loaded statically by the HTML page and a DynamicXAP which is loaded from code within the initial XAP. The DynamicXAP is loaded with code similar to this:
var asm = LoadAssemblyFromXap(stream, "DLLName");
// LoadAssemblyFromXAP will load the DynamicXAP as a file stream,
// unpack it and load DLLName as a dll.
var controllerType = asm.GetType("ClassNameToInstantiate_InsideAsm");
var constructor = controllerType.GetConstructor(Type.EmptyTypes);
return constructor.Invoke(null);
I have a class which uses reflection (specifically FieldInfo.GetValue) to do data binding. This class is defined in the InitialXAP. If I try to use this class in the DynamicXAP, I get an error:
Message: Unhandled Error in Silverlight Application System.FieldAccessException: Class.In.DynamicXAP.Which.Uses.The.Reflection.Class.In.InitialXAP
at System.Reflection.RtFieldInfo.PerformVisibilityCheckOnField(IntPtr field, Object target, IntPtr declaringType, FieldAttributes attr, UInt32 invocationFlags)
at System.Reflection.RtFieldInfo.InternalGetValue(Object obj, Boolean doVisibilityCheck, Boolean doCheckConsistency)
at System.Reflection.RtFieldInfo.InternalGetValue(Object obj, Boolean doVisibilityCheck)
at System.Reflection.RtFieldInfo.GetValue(Object obj)
I can get around this error by creating a subclass of the class using reflection and overriding the method using reflection like so:
public class InitialXAP.ClassUsingReflection {
public virtual object GetValue()
{
return fieldInfo.GetValue(parent);
}
}
public class ClassUsingReflection : InitialXAP.ClassUsingReflection {
public override object GetValue()
{
return fieldInfo.GetValue(parent);
}
}
But I would prefer to avoid this duplication by allowing reflection from the InitialXAP in the DynamicXAP. Any ideas on what I can do?
Although there is a learning curve, I would look at Silverlight MEF or Prism (both are together at last in the latest Prism 4 Beta). They both support dynamic loading of modules and enforce good patterns for reuse and separate/team development.
InitialXAP.ClassUsingReflection...
Note the duplicate isn't part of the inital xap namespace (ClassUsingReflection), and may be imported.
Notice GetVisible - as in not visible to Dynamic xap...
Just leave the duplicate (take away base class obviously) and try.