Archive for the ‘WPF’ Category

Getting WPF Control Template in IronPython

October 14, 2009 Leave a comment

I always find myself needing a control template so I can customize one of the WPF controls. I used to fire up Expression Blend to get it, and then realized I could write a little IronPython code to do it. Paste this code into the IronPython 2.0 or 2.6 console to see it work!

import clr
from System.Windows import Window
from System.Windows.Controls import *
from System.Windows.Markup import XamlWriter
from System.Xml import XmlWriter, XmlWriterSettings
from System.Text import StringBuilder

# Need to render the control on screen so it will have a Control Template
def getControlTemplate(ctl):
   "Gets the control template for a WPF control"
   window = Window()
   window.Content = ctl
   return ctl.Template

settings = XmlWriterSettings()
settings.Indent = True
settings.IndentChars = "   "
sb = StringBuilder()
writer = XmlWriter.Create(sb,settings)
### replace Button() with an instance of whatever control you want. ###
XamlWriter.Save(getControlTemplate(Button()), writer)
print (sb.ToString())

Reference to Self in XAML

April 9, 2009 3 comments

I’m always finding that I need to get a reference to the root element (this) in my XAML markup. If I’m in a situation that I can use a Binding, I can do something like this where I’m getting the Height of the current Window):

{Binding RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type Window}}, Path=Height}

However, there are many times that I need a reference to the root where I can’t use a binding. I really, really hope somebody will prove me wrong and show me there is a better way to do this that’s already built in to WPF, but since I haven’t been able to find anything, I added a MarkupExtension that uses reflection to get a reference to the private fields serviceProvider._Context._rootElement:

public class SelfExtension : MarkupExtension
    public override object ProvideValue(IServiceProvider serviceProvider)
        object self = null;
        Type selfType = serviceProvider.GetType();
        FieldInfo contextFieldInfo = selfType.GetField("_context", BindingFlags.NonPublic | BindingFlags.Instance);
        if(contextFieldInfo != null)
            object context = contextFieldInfo.GetValue(serviceProvider);
            Type contextType = context.GetType();
            FieldInfo rootElementFieldInfo = contextType.GetField("_rootElement", BindingFlags.NonPublic | BindingFlags.Instance);
            if(rootElementFieldInfo != null)
                self = rootElementFieldInfo.GetValue(context);
        return self;

Yes, this is a terrible hack using reflection to access private fields, and there’s a good chance it will go away in a future version of WPF…hopefully because Microsoft builds in their own extension to do this properly. If you know of a better way, please speak up!

[Update: Microsoft addressed this is .NET 4]

Here is a new version that doesn’t require reflection using the updated API in .NET 4:

public class SelfExtension : MarkupExtension
    public override object ProvideValue(IServiceProvider serviceProvider)
        return ((System.Xaml.IRootObjectProvider)serviceProvider).RootObject;
Categories: WPF Tags: , , , ,

Loading an Object from XAML Markup

March 30, 2009 Leave a comment

I’ve got to say that my absolute favorite feature of WPF is that you can create your entire user interface in a string of XAML.

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Using Reflection in WPF

March 30, 2009 Leave a comment

Reflection is a very powerful tool for building code that is highly customizable at runtime, making it very reusable. If you’re going to make an application that is primarily loose XAML, you will want to make whatever code you do write as flexible as possible, and to do so, it helps to have a firm grasp of reflection.

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Model-View-Controller with WPF

March 30, 2009 Leave a comment

With WPF, it is very simple follow the MVC pattern where a CLR object or XML is acting as your Model, and you want to present the data from the Model in a View, which is built in XAML by binding WPF controls to elements in the Model. What happens when we want to make changes to the data in the Model, such as updating some properties of that object? Your user is interacting with the View, so you need something in between the View and the Model, which is your Controller.

The most common approach to updating the data is to write event handlers in the code behind for your XAML file (your View). However, this means that your Controller logic is tightly coupled with your View…you can’t easily reuse it in another View. If you implement your Controller logic as a WPF ICommand, you can keep the logic in a different class and use it declaratively from any XAML file.

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