DependencyProperties與Bools：False導致事件不會觸發

Question

所以我爲我的xaml用戶控件創建了一個布爾依賴項屬性。但是，當xaml中的值設置爲false時，它在xaml中設置爲true時不觸發事件。無論如何，我怎樣才能把它發射出去？

public static readonly DependencyProperty AvailableProperty = 
    DependencyProperty.Register("Available", typeof(bool), typeof(DetailPannel), 
    new PropertyMetadata(null, onAvailablePropertyChanged)); 

public bool Available 
{ 
    get { return (bool)GetValue(AvailableProperty); } 
    set { SetValue(AvailableProperty, value); } 
} 

private async static void onAvailablePropertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e) 
{ 
    var obj = d as DetailPannel; 
    bool avaible = (bool.Parse(e.NewValue.ToString())); 
    if(avaible == false) 
    {    
     obj.PreviewImage.Source = await ConvertToGreyscale(obj.PreviewImage); 
     obj.StateRelatedImage.Source = new BitmapImage(new Uri("ms-appx:///icon.png")); 
    } 
} 

Answer 1

值null對bool屬性無效。更改PropertyMetadata，指定發送false或true爲默認值：

public static readonly DependencyProperty AvailableProperty = 
    DependencyProperty.Register("Available", typeof(bool), typeof(DetailPannel), 
    new PropertyMetadata(false, onAvailablePropertyChanged)); 

而且在你的PropertyChanged處理程序的代碼看起來可疑。不要使用bool.Parse，但只投e.NewValue到bool：

private async static void onAvailablePropertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e) 
{ 
    var obj = d as DetailPannel; 
    var available = (bool)e.NewValue; 

    if (!available) 
    { 
     ... 
    } 
}