Всем привет. Создаю userControl В нем - ContentPresenter Создаю DependencyProperty для ContentPresenter.Content В MainPage вставляю userControl В его DependencyProperty вставляю TextBlock и даю ему имя При запуске приложения вижу, что в объекте MainPage есть поле с названием TextBlock, но оно null Хотя на экране все ок Ниже код. Я ставлю в дебаггере точку останова на операции в методе Button_Click четко видно что this.MyLabel равно null. Вылетает ArgumentNullException Если присвоить имя созданному userControl или любому другому контролу - все ок. Я думаю, что проблема где-то в реализации DependencyProperty - реализация необычная и дает много возможностей (по сути дает в Silverlight возможности WPF DependencyProperty) Либо же это баг Silverlight Вот здесь лежит архив с кодом проекта и сниппетом для DependencyProperty: iFolderПомогите пожалуйста разобраться с проблемой | Код |
<UserControl x:Class="TestApp.SomeContainer"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
mc:Ignorable="d"
d:DesignHeight="300" d:DesignWidth="400">
<Grid x:Name="LayoutRoot" Background="White">
<ContentPresenter x:Name="MyCP"/>
</Grid>
</UserControl>
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| Код |
using System;
using System.Windows;
using System.Windows.Controls;
namespace TestApp {
public partial class SomeContainer : UserControl {
public SomeContainer() {
InitializeComponent();
MyContentChanged += new RoutedPropertyChangedEventHandler<FrameworkElement>(SomeContainer_MyContentChanged);
//apply default values to the View
this.SomeContainer_MyContentChanged(null, null);
}
#region Event handlers
//bridge between two objects - DependencyProperty and ContentPresenter
//This EH used when dependencyProperty changed from code
void SomeContainer_MyContentChanged(object sender, RoutedPropertyChangedEventArgs<FrameworkElement> e) {
this.MyCP.Content = this.MyContent;
}
#endregion Event handlers
#region public FrameworkElement MyContent
/// <summary>
/// Gets or sets the value of MyContent dependency property.
/// </summary>
public FrameworkElement MyContent {
get { return (FrameworkElement)GetValue(MyContentProperty); }
set { SetValue(MyContentProperty, value); }
}
/// <summary>
/// Identifies the MyContent dependency property.
/// </summary>
public static readonly DependencyProperty MyContentProperty =
DependencyProperty.Register(
"MyContent",
typeof(FrameworkElement),
typeof(SomeContainer),
new PropertyMetadata(null, OnMyContentPropertyChanged));
/// <summary>
/// MyContentProperty property changed handler.
/// </summary>
/// <param name="d">SomeContainer that changed its MyContent.</param>
/// <param name="e">Event arguments.</param>
private static void OnMyContentPropertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e) {
SomeContainer source = (SomeContainer)d;
FrameworkElement newValue = (FrameworkElement)e.NewValue;
FrameworkElement oldValue = (FrameworkElement)e.OldValue;
// validate newValue
if (!IsValidMyContent(source, oldValue, newValue)) {
// revert back to e.OldValue
source._nestLevelMyContent++;
source.SetValue(e.Property, e.OldValue);
source._nestLevelMyContent--;
// throw ArgumentException
throw new ArgumentException("Invalid MyContentProperty value", "e");
}
if (source._nestLevelMyContent == 0) {
// remember initial state
source._initialMyContent = oldValue;
source._requestedMyContent = newValue;
}
source._nestLevelMyContent++;
// coerce newValue
FrameworkElement coercedValue = (FrameworkElement)CoerceMyContent(d, e.NewValue);
if (newValue != coercedValue) {
// always set MyContentProperty to coerced value
source.MyContent = coercedValue;
}
source._nestLevelMyContent--;
if (source._nestLevelMyContent == 0 && source.MyContent != source._initialMyContent) {
// fire changed event only at root level and when there is indeed a change
source.OnMyContentChanged(oldValue, source.MyContent);
}
}
/// <summary>
/// MyContentProperty validation handler.
/// </summary>
/// <param name="value">New value of MyContentProperty.</param>
/// <returns>
/// Returns true if value is valid for MyContentProperty, false otherwise.
/// </returns>
private static bool IsValidMyContent(SomeContainer source, FrameworkElement oldValue, FrameworkElement newValue) {
//place here your code for validating new value (if you need)
//return false if newValue equals oldValue
if (newValue.Equals(oldValue)) { return false; }
return true;
}
/// <summary>
/// MyContentProperty coercion handler.
/// </summary>
/// <param name="d">SomeContainer that changed its MyContent.</param>
/// <param name="value">Event arguments.</param>
/// <returns>
/// Coerced effective value of MyContentProperty from input parameter value.
/// </returns>
private static object CoerceMyContent(DependencyObject d, object value) {
SomeContainer source = (SomeContainer)d;
FrameworkElement newValue = (FrameworkElement)value;
//place here your code (if you need)
return newValue;
}
/// <summary>
/// MyContentProperty changed event.
/// </summary>
public event RoutedPropertyChangedEventHandler<FrameworkElement> MyContentChanged;
/// <summary>
/// Called by OnMyContentPropertyChanged static method to fire MyContentChanged event.
/// </summary>
/// <param name="oldValue">The old value of MyContent.</param>
/// <param name="newValue">The new value of MyContent.</param>
protected virtual void OnMyContentChanged(FrameworkElement oldValue, FrameworkElement newValue) {
//place here your code (if you need)
RoutedPropertyChangedEventArgs<FrameworkElement> e =
new RoutedPropertyChangedEventArgs<FrameworkElement>(oldValue, newValue);
if (MyContentChanged != null) {
MyContentChanged(this, e);
}
}
/// <summary>
/// Cached previous value of MyContentProperty.
/// </summary>
private FrameworkElement _initialMyContent = null;
/// <summary>
/// Cached originally requested value of MyContentProperty by user.
/// </summary>
private FrameworkElement _requestedMyContent;
/// <summary>
/// level of recursive calls of PropertyChangedCallback, for implementing validation & coercion,
/// and preventing internal transitions from visible to client by not firing bogus changed notifications
/// </summary>
private int _nestLevelMyContent;
#endregion public FrameworkElement MyContent
}
}
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| Код |
<UserControl x:Class="TestApp.MainPage"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:local="clr-namespace:TestApp"
mc:Ignorable="d"
d:DesignHeight="300"
d:DesignWidth="400">
<Grid x:Name="LayoutRoot"
Background="White">
<StackPanel Width="300">
<Button Content="click it!"
Click="Button_Click"
Height="30" />
<local:SomeContainer>
<local:SomeContainer.MyContent>
<TextBlock x:Name="MyLabel"
Text="Any text" />
</local:SomeContainer.MyContent>
</local:SomeContainer>
</StackPanel>
</Grid>
</UserControl>
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| Код |
using System.Windows;
using System.Windows.Controls;
namespace TestApp {
public partial class MainPage : UserControl {
public MainPage() {
InitializeComponent();
}
private void Button_Click(object sender, RoutedEventArgs e) {
this.MyLabel.Text = "hellow from code";
}
}
}
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userControl-> DepProp -> ContentPresenter 
Загрузка ...
