如何控制控件的加载顺序？

Question

My English skill is poor because I'm not a native English speaker.

My application has a MainWindowView and MainWindowBehavior also MainWindowView has control(Editor) as the following code.

<MainWindowView>
  <Grid>
    <TabControl>
      <TabItem>
        <Grid>
          <Editor x:Name="editor"/>
        </Grid>
      </TabItem>
    </TabControl>
  </Grid>

  <i:Interaction.Behaviors>
    <behaviors:MainWindowBehavior/>
  </i:Interaction.Behaviors>
</MainWindowView>

MainWindowBehavior uses the property of Editor in the LoadedEventHandler of MainWindowView. The following code shows the above logic.

protected override void OnDetaching()
{
    this.AssociatedObject.Loaded -= AssociatedObject_Loaded;

    base.OnDetaching();
}

protected override void OnAttached()
{
    base.OnAttached();

    this.AssociatedObject.Loaded += AssociatedObject_Loaded;
}

private void AssociatedObject_Loaded(object sender, RoutedEventArgs e)
{
    this.mainWindow = sender as MainWindow;

    // run time error
    this.mainWindow.editor.Parser.ParsingFailed += Parser_ParsingFailed;
}

But compiler shows run time error because of the value of the Parser property of the editor is null. I tried to initialize the parser property of the editor at the Constructer, OnApplyTemplate function, Loaded EventHandler but 3 cases all called late than Loaded EventHandler of MainWindow.

And as a result, generate run time error.

I think that the Loaded EventHandler of the editor must be called early more Loaded EventHandler of the MainWindowBehavior. But in fact, the sequence reverse.

I don't know why the sequence reverse.

How can I change the loading sequence as I thought?

Thank you for reading.

Answer 1

Maybe you cannot change the sequence of events, but you can sure change the way you listen to these events. I suggest you to hook-up to an event in your mainWindow that will indicate you when its editor property is set.

Your code would become:

private void AssociatedObject_Loaded(object sender, RoutedEventArgs e)
{
    this.mainWindow = sender as MainWindow;
    // Here we don't access mainWindow.editor anymore, we hook-up to an event instead
    this.mainWindow.OnEditorPropertyChanged += MainWindow_EditorPropertyChanged;
}

private void MainWindow_EditorPropertyChanged(object sender){
{
    var mainWindow = sender as MainWindow;
    if (mainWindow.editor != null) {
        mainWindow.editor.Parser.ParsingFailed += Parser_ParsingFailed;
    }
}

And in your MainWindow , make sure to raise an event when its editor property is set, for example:

public delegate void OnEditorPropertyChangedEventHandler(object sender);

public event OnEditorPropertyChangedEventHandler OnEditorPropertyChanged;

// Backing field
private Editor _editor;

public Editor editor {
    get => _editor;
    set => {
        _editor = value;
        OnEditorPropertyChanged?.Invoke(this); // Raise the event
    }
}

Answer 2

I found the cause of my problem while following your advice.

I think the OnApplyTemplate function of the Editor is called early than the Loaded event of the MainWindowView. But, in fact, the OnApplyTemplate function of the Editor is not called.

I have been apprehending wrong about my problem. I'm sorry... Now I would make my problem right.

The Editor is Custom-Control. I missed adding code in the Generic.xaml file the following code.

<ResourceDictionary.MergedDictionaries>
    <ResourceDictionary Source="/WpfControls;component/Themes/Editor.xaml"/>
</ResourceDictionary.MergedDictionaries>

Now I added the above code in the Generic.xaml and the OnApplyTemplate function of Editor is called normally also it is called early than the Loaded event of the MainWindowView.

Thank you for your help and interest in my problem.