我有一个 FrameworkElement的（真的切换按钮）的内容里面，一个弹出。

我访问它是这样的：

 切换按钮按钮=（切换按钮）发送;
弹出弹出=（弹出）button.FindName（popSelectIteration）;
 

通常能正常工作。但有时弹出空。

我试图找到一种方法来调试这一点。有没有一种方法枚举所有的东西是FindName能找到？

作为背景，这里是如何我的弹出窗口中切换按钮定义的：

 ＆LT;切换按钮Grid.Column =1的Horizo​​ntalAlignment =右保证金=0,2,0,2选中=btnFindIterationChecked＆GT;
 ＆LT;电网＆GT;
  ＆LT;弹出PlacementTarget ={结合的ElementName = chkIteration}NAME =popSelectIteration关=popSelectIteration_Closed
     AllowsTransparency =真StaysOpen =FALSEPopupAnimation =变脸＆GT;
      ＆LT; BORDER BorderBrush =＃FF000000背景=浅蓝色了borderThickness =1,1,1,1CornerRadius =8,8,8,8填充=5＆GT;
        ＆LT;电网＆GT;
          ＆LT; Grid.RowDefinitions＆GT;
            ＆LT; RowDefinition高度=自动＆GT;＆LT; / RowDefinition＆GT;
            ＆LT; RowDefinition高度=300＆GT;＆LT; / RowDefinition＆GT;
            ＆LT; RowDefinition高度=自动＆GT;＆LT; / RowDefinition＆GT;
          ＆LT; /Grid.RowDefinitions>
          ＆LT; TextBlock的前景=黑＆GT;选择目标：LT; / TextBlock的＆GT;
          ＆所述;的ScrollViewer Grid.Row =1＆GT;
            ＆LT; TreeView控件的ItemsSource ={结合IterationTree}SelectedItemChanged =TreeView_SelectedItemChanged＆GT;
              ＆LT; TreeView.ItemTemplate＆GT;
                ＆LT; HierarchicalDataTemplate的ItemsSource ={结合儿童}＆GT;
                  ＆LT; StackPanel的方向=横向＆GT;
                    ＆LT; TextBlock的文本={结合PathEnd}/＆GT;
                  ＆LT; / StackPanel的＆GT;
                ＆LT; / HierarchicalDataTemplate＆GT;
              ＆LT; /TreeView.ItemTemplate>
            ＆LT; /树视图＆GT;
          ＆LT; /的ScrollViewer＆GT;
          ＆LT;按钮Grid.Row =2背景=浅蓝色CONTENT =清除选择单击=btnClear_Click/＆GT;
        ＆LT; /网格＆GT;
      ＆LT; /边框＆GT;
    ＆LT; /弹出＆GT;
  ＆LT; /网格＆GT;
＆LT; /切换按钮＆GT;
 

解决方案

尝试探听。这是一个伟大的WPF调试工具的一切涉及可视树。

修改：您的特定问题似乎是一个时间问题，但。我想这树没有完全建成还没有与您试图访问一个子元素，虽然它不创建。等待，直到最顶端的元素收到一个装事件。

I have a FrameworkElement (really a ToggleButton) that has inside its content a Popup.

I access it like this:

ToggleButton button = (ToggleButton)sender;
Popup popup = (Popup)button.FindName("popSelectIteration");

Usually this works fine. But sometimes popup is null.

I am trying to find a way to debug this. Is there a way enumerate all the "things" that FindName could find?

As background, here is how my popup is defined in the ToggleButton:

<ToggleButton Grid.Column="1" HorizontalAlignment="Right" Margin="0,2,0,2" Checked="btnFindIterationChecked">
 <Grid>
  <Popup PlacementTarget="{Binding ElementName=chkIteration}"  Name="popSelectIteration" Closed="popSelectIteration_Closed"
     AllowsTransparency="True" StaysOpen="False" PopupAnimation="Fade">
      <Border BorderBrush="#FF000000" Background="LightBlue" BorderThickness="1,1,1,1" CornerRadius="8,8,8,8" Padding="5">
        <Grid>
          <Grid.RowDefinitions>
            <RowDefinition Height="Auto"></RowDefinition>
            <RowDefinition Height="300"></RowDefinition>
            <RowDefinition Height="Auto"></RowDefinition>
          </Grid.RowDefinitions>
          <TextBlock Foreground="Black" >Select Destination:</TextBlock>
          <ScrollViewer Grid.Row="1" >
            <TreeView ItemsSource="{Binding IterationTree}" SelectedItemChanged="TreeView_SelectedItemChanged">
              <TreeView.ItemTemplate>
                <HierarchicalDataTemplate ItemsSource="{Binding Children}">
                  <StackPanel Orientation="Horizontal">
                    <TextBlock Text="{Binding PathEnd}" />
                  </StackPanel>
                </HierarchicalDataTemplate>
              </TreeView.ItemTemplate>
            </TreeView>
          </ScrollViewer>
          <Button Grid.Row="2" Background="LightBlue" Content="Clear Selection" Click="btnClear_Click"/>
        </Grid>
      </Border>
    </Popup>
  </Grid>
</ToggleButton>

Try Snoop. It is a great WPF debugging utility for everything that concerns the visual tree.

Edit: Your specific problem seems to be a timing issue though. I guess that the tree is not completely constructed yet and you try to access a child element although it is not created. Wait until the topmost element receives a "Loaded" event.