内部管理DependencyProperty值和更改的回调 [英] Internal management of DependencyProperty value and Changed callbacks

问题描述

我认为这是关于如何管理依赖项属性的基本误解，但我似乎找不到一个明确的例子来纠正我。

请看以下内容代码示例...

 公共类MyControl 
 {
 public static readonly DependencyProperty ExpressionProperty = 
 DependencyProperty.Register（ Expression，
 typeof（Expression），
 typeof（MyControl），
 new PropertyMetadata（ExpressionChanged））; 
 
 public Expression Expression 
 {
 get {return（Expression）GetValue（ExpressionProperty）; } 
 set {SetValue（ExpressionProperty，value）; } 
} 
 
私有静态无效ExpressionChanged（DependencyObjectdependencyObject，DependencyPropertyChangedEventArgsdependencyPropertyChangedEventArgs）
 {
 ...必须响应属性
的外部更改。 。更新用户界面以反映对属性
}的外部更改
 
 private void RespondToInput（）
 {
 ...对表达式执行操作，添加新元素或执行某些操作b $ b ...现在表达式已更改，因此我想更新依赖项属性
 ...，以便datacontext获取新值。 
 SetValue（ExpressionProperty，updatedExpression）; 
} 
} 
  

我不明白的是，当我这样做时在RespondToInput工作时，我现在想更新DependencyProperty，但如果这样做，则调用PropertyChanged回调，这时我走了一圈，现在就开始更新UI，即使我已从UI有效地发起了更改。 / p>

我不知道这是否足够合理。

我做错了什么？

谢谢！

解决方案

您不能阻止在以下情况下调用PropertyChangedCallback属性值更改。您可以做的是对内部属性更改不做出反应：

  private bool isInternalExpressionChanged; 
 
私有静态无效ExpressionChanged（DependencyObjectdependencyObject，DependencyPropertyChangedEventArgsdependencyPropertyChangedEventArgs）
 {
 if（！isInternalExpressionChanged）
 {
 ... 
} 
} 
 
 private void RespondToInput（）
 {
 ... 
 isInternalExpressionChanged = true; 
 SetValue（ExpressionProperty，updatedExpression）; 
 isInternalExpressionChanged = false; 
} 
  

I think this is a basic misunderstanding about how to manage dependency properties but I can't seem to find a clear example to correct me.

Looking at the following code as an example...

public class MyControl
{
    public static readonly DependencyProperty ExpressionProperty = 
                                    DependencyProperty.Register("Expression",
                                    typeof (Expression),
                                    typeof (MyControl),
                                    new PropertyMetadata(ExpressionChanged));

    public Expression Expression
    {
        get { return (Expression)GetValue(ExpressionProperty); }
        set { SetValue(ExpressionProperty, value); }
    }

    private static void ExpressionChanged(DependencyObject dependencyObject, DependencyPropertyChangedEventArgs dependencyPropertyChangedEventArgs)
    {
        ... Must respond to external change of property
        ... Update UI to reflect external change to property
    }

    private void RespondToInput()
    {
        ... Do something to expression, add new elements or something
        ... Now expression has changed so I want to update the dependency property
        ... so datacontext gets new value.
        SetValue(ExpressionProperty, updatedExpression);
    }
}

What I don't understand is that when I do the RespondToInput work, I want to now update the DependencyProperty, but if I do, the PropertyChanged callback is called, at which point I go in a circle and now start updating the UI, even though I initiated the change from the UI effectively.

I don't know if that makes enough sense.

What did I do wrong??

Thanks!

解决方案

You can't prevent the PropertyChangedCallback from being called when the property value changes. What you can do is not to react on an internal property change:

private bool isInternalExpressionChanged;

private static void ExpressionChanged(DependencyObject dependencyObject, DependencyPropertyChangedEventArgs dependencyPropertyChangedEventArgs)
{
    if (!isInternalExpressionChanged)
    {
        ...
    }
}

private void RespondToInput()
{
    ...
    isInternalExpressionChanged = true;
    SetValue(ExpressionProperty, updatedExpression);
    isInternalExpressionChanged = false;
}

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