在用wpf的时候发现个奇怪的问题：在嵌套的控件里面，如果有控件调用了事件处理程序和使用了ContentTemplateSelector时，程序就会提示：Object reference not set to an instance of an object.。删掉其中任何一个就不会出错
When
in use wpf found a strange problem: nested controls inside, if the control calls the event handler and use the ContentTemplateSelector, the program will prompt: Object reference not set to an instance of an object.. Delete
any of them will not go wrong
源码如下，删除下面的Click或者ContentTemplateSelector就正常，同时存在就会报错：
Source as follows, delete the following Click or ContentTemplateSelector to normal, while there will be error
<Window x:Class="TestApp.MainWindow" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:control="clr-namespace:TestApp" Title="MainWindow" Height="350" Width="525"> <Window.Resources> <control:MyTemplateSelector x:Key="bbb"></control:MyTemplateSelector> </Window.Resources> <ItemsControl ItemsSource="{Binding}"> <ItemsControl.ItemTemplate> <DataTemplate > <ItemsControl ItemsSource="{Binding}" DataContext="{Binding Path=ItemsSource, RelativeSource={RelativeSource AncestorType=ItemsControl,Mode=FindAncestor}}"> <ItemsControl.ItemTemplate> <DataTemplate > <WrapPanel > <Button Cursor="Hand" Content="bbbbbbbb" Height="23" Width="75" Click="ShowContextMenu" > </Button> <ContentControl Content="aa" ContentTemplateSelector="{StaticResource
bbb}" /> </WrapPanel> </DataTemplate> </ItemsControl.ItemTemplate> </ItemsControl> </DataTemplate> </ItemsControl.ItemTemplate> </ItemsControl></Window>
<Window x:Class="TestApp.MainWindow" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:control="clr-namespace:TestApp" Title="MainWindow" Height="350" Width="525"> <Window.Resources> <control:MyTemplateSelector x:Key="bbb"></control:MyTemplateSelector> </Window.Resources> <ItemsControl ItemsSource="{Binding}"> <ItemsControl.ItemTemplate> <DataTemplate > <ItemsControl ItemsSource="{Binding}" DataContext="{Binding Path=ItemsSource, RelativeSource={RelativeSource AncestorType=ItemsControl,Mode=FindAncestor}}"> <ItemsControl.ItemTemplate> <DataTemplate > <WrapPanel > <Button Cursor="Hand" Content="bbbbbbbb" Height="23" Width="75" Click="ShowContextMenu" > </Button> <ContentControl Content="aa" ContentTemplateSelector="{StaticResource
bbb}" /> </WrapPanel> </DataTemplate> </ItemsControl.ItemTemplate> </ItemsControl> </DataTemplate> </ItemsControl.ItemTemplate> </ItemsControl></Window>
cs源码：
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;
namespace TestApp
{
/// <summary>
/// Interaction logic for MainWindow.xaml
/// </summary>
public partial class MainWindow : Window
{
public MainWindow()
{
InitializeComponent();
List<TestClass> data = new List<TestClass>();
data.Add(new TestClass() { date = "aaaa", name = "aa1", username ="姓名"});
data.Add(new TestClass() { date = "bbb", name = "bbb", username = "姓名1" });
this.DataContext = data;
}
private void ShowContextMenu(object sender, RoutedEventArgs e)
{
}
}
public class TestClass:System.ComponentModel.INotifyPropertyChanged
{
public string name
{
get;
set;
}
public string date
{
get;
set;
}
public string username
{
get;
set;
}
public event System.ComponentModel.PropertyChangedEventHandler PropertyChanged;
}
public class MyTemplateSelector : DataTemplateSelector
{
public override DataTemplate SelectTemplate(object item, DependencyObject container)
{
return null;
}
}
}