如果拥有一个带有DependencyProperty的自己的用户控件和相应的回调方法,如下所示：
public partial class PieChart : UserControl
{
public static readonly DependencyProperty RatesProperty = DependencyProperty.Register("Rates",typeof(ObservableCollection<double>),typeof(PieChart),new PropertyMetadata(new ObservableCollection<double>() { 1.0,1.0 },new PropertyChangedCallback(OnRatesChanged)));
[...]
public static void OnRatesChanged(DependencyObject d,DependencyPropertyChangedEventArgs e)
{
((PieChart)d).drawChart();
}
使用此用户控件时,我将名为“Rates”的ObservableCollection绑定到RatesProperty.费率和相关方法如下所示：
private ObservableCollection<double> rates;
public ObservableCollection<double> Rates
{
get { return this.rates; }
set
{
if (this.rates != value)
{
this.rates = value;
OnPropertyChanged("Rates");
}
}
}
public event PropertyChangedEventHandler PropertyChanged;
protected virtual void OnPropertyChanged(string propertyName)
{
if (PropertyChanged != null)
PropertyChanged(this,new PropertyChangedEventArgs(propertyName));
}
当我更改ObservableCollection Rate(例如,使用this.Rates = new ObservableCollection< double>(){1.0,2.0})时,将调用用户控件的OnRatesChanged()方法,如预期.但是当我执行以下操作时,它不会被调用：
this.Rates[0] = (double)1;
this.Rates[1] = (double)2;
OnPropertyChanged("Rates");
我期望当我使用正确的属性名称引发PropertyChanged事件时,始终会调用用户控件中的相应回调.那是错的吗？
我找到了这个帖子：Getting PropertyChangedCallback of a dependency property always – Silverlight
它涵盖了silverlight,但我认为在WPF中也是如此.
所以后台的框架检查绑定属性(在我的示例中为“Rates”)是否发生了变化,只有当它发生变化时才调用相关的回调,对吗？因此改变我的收藏元素没有任何效果,我总是要改变完整的收藏？
谢谢！
您的结论是正确的,只有在将rates依赖项属性设置为新集合(或null)时,才会调用OnRatesChanged回调.
为了获得有关集合更改的通知,您还必须注册NotifyCollectionChangedEventHandler：
private static void OnRatesChanged(
DependencyObject d,DependencyPropertyChangedEventArgs e)
{
var pieChart = (PieChart)d;
var oldRates = e.OldValue as INotifyCollectionChanged;
var newRates = e.NewValue as INotifyCollectionChanged;
if (oldRates != null)
{
oldRates.CollectionChanged -= pieChart.OnRatesCollectionChanged;
}
if (newRates != null)
{
newRates.CollectionChanged += pieChart.OnRatesCollectionChanged;
}
pieChart.drawChart();
}
private void OnRatesCollectionChanged(
object sender,NotifyCollectionChangedEventArgs e)
{
switch (e.Action)
{
...
}
drawChart();
}
