如何从 xaml 获取显式指定的属性

Question

I have a loop with children of a grid. For every child, I want to know which properties have been specified explicitly in the XAML code. Do I have a chance to find out?

For example: I have a TextBox

<TextBox Height="150"/>

Only the property Height is given by XAML-Code. How I can find it out in the c# Code? In other words, I don't want all of the properties of the TextBox, but only those who are specified in the XAML.

Answer 1

This was a challenging question, but luckily for you, I like a good challenge. So initially, I found the DependencyPropertyHelper.GetValueSource method . This method takes a DependencyObject and a DependencyProperty and returns a ValueSource struct :

ValueSource valueSource = DependencyPropertyHelper.GetValueSource(SomeTextBlock, 
    TextBlock.TextWrappingProperty);

The ValueSource struct has a BaseValueSource enum property which has the following members:

These values relate to the list of DependencyProperty precedences and specify the different ways that a DependencyProperty value can be changed. A BaseValueSource enum instance value of Local means that the property was set locally using the SetValue method... this will also include instances where a property was set in code using the SetValue method. The Framework uses this method to set values from XAML markup.

The only problem was that we'd now have to find a collection of all of the DependencyProperty s of a particular DependencyObject so that we could call the above method on each to see if it was set by the SetValue method. I was hoping that Microsoft would have given us something to do this for us, but it appears not.

After a quick search, I found a way to do this using Reflection in the List properties of a DependencyObject? post here on StackOverflow. However, I kept looking and then came across a better method... a much better method. I found it in the Getting list of all dependency/attached properties of an Object question on the Visual Studio Forum.

If you look down that page at the answer from Zhou Yong, you can find a DependencyPropertyHelper class that he created. At first I thought 'let me just run this DependencyPropertyHelper.GetValueSource method to see what I get' and was expecting a long list of all of the DependencyProperty s of the TextBlock .

However, it turns out that what comes out of this method is exactly what you're after. It only returns the properties that have actually been set in XAML . In his code, I see a MarkupObject , a MarkupProperty and a MarkupWriter . I've not used these before, but it seems that this is actually looking at the XAML defined for the TextBlock . So in helping you, I've actually learned some new things too... +1 good question.

Bearing that in mind, I believe that you can ignore the earlier part of my answer regarding the ValueSource struct and just use that method. Let me know If you need any more help.

Answer 2

You could inherit the TextBox in your own code. The PropertyChanged could then be overriden and you would receive any properties changing.

public class MyTextBox : TextBox
{
    public MyTextBox()
    {
    }

    protected override void OnPropertyChanged(DependencyPropertyChangedEventArgs e)
    {
        Console.WriteLine(string.Format("Property changed: {0} {1}", e.Property.Name, e.NewValue));

        base.OnPropertyChanged(e);
    }
}

<Window x:Class="WpfApplication1.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="clr-namespace:WpfApplication1"
    Title="MainWindow" Height="350" Width="525">
<Grid>
    <local:MyTextBox x:Name="TB" Height="150"></local:MyTextBox>
</Grid>
</Window>

Unfortunatly you will also receive properties changed by styles

Here's the result of the code above

Property changed: UndoManagerInstance MS.Internal.Documents.UndoManager

Property changed: Instance System.Windows.Documents.TextEditor

Property changed: XmlnsDictionary System.Windows.Markup.XmlnsDictionary

Property changed: IWindowService WpfApplication1.MainWindow

Property changed: Name TB

Property changed: Height 150

Property changed: Background #FFFFFFFF

Property changed: BorderBrush #FFABADB3

Property changed: Foreground #FF000000

Property changed: BorderThickness 1,1,1,1

Property changed: TabNavigation None

Property changed: FocusVisualStyle

Property changed: AllowDrop True

Property changed: PanningMode VerticalFirst

Property changed: IsFlicksEnabled False

Property changed: Template System.Windows.Controls.ControlTemplate

Property changed: XmlNamespaceMaps System.Collections.Hashtable

Property changed: XmlnsDictionary System.Windows.Markup.XmlnsDictionary

Property changed: XmlNamespaceMaps System.Collections.Hashtable

Property changed: IsVisible True

Property changed: ActualWidth 509

Property changed: ActualHeight 150

Property changed: PageHeight 148

Answer 3

根据 Sheridan's answer 中提供的链接，这里是获取 XAML 中元素上设置的所有属性所需的非常小的代码片段：

MarkupWriter.GetMarkupObjectFor(element).Properties