有一個定時器來定期觸發PropertyChanged
事件是一種方法。但是,如果ContentControl
中有大量物品,並且您要更新的物品位於該ContentControl
的ItemTemplate
中,則意味着不必要地創建了100多個定時器,並讓它們同時全部升起。但是,在ItemsControl
(如ListBox
)中使用時,仍然會爲每個項目創建此行爲。
由於這個原因,我創建了這種行爲,只會在您的模板中爲每個 綁定創建一次。它也是純粹的MVVM。
使用
<Label xmlns:b="clr-namespace:Lloyd.Shared.Behaviors"
xmlns:i="http://schemas.microsoft.com/expression/2010/interactivity"
Content="{Binding MyContent}" Width="80" Foreground="{Binding MyColor}">
<i:Interaction.Behaviors>
<b:PeriodicBindingUpdateBehavior Interval="0:00:01" Property="{x:Static ContentControl.ContentProperty}" Mode="UpdateTarget" />
<b:PeriodicBindingUpdateBehavior Interval="0:00:01" Property="{x:Static Control.ForegroundProperty}" Mode="UpdateTarget" />
</i:Interaction.Behaviors>
</Label>
依賴
注意http://schemas.microsoft.com/expression/2010/interactivity命名空間是可用的NuGet包叫做System.Windows.Interactivity.WPF
下。如果您打開混合項目,它也會自動添加。
複製和粘貼代碼
using System;
using System.Threading;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Data;
using System.Windows.Interactivity;
namespace Lloyd.Shared.Behaviors
{
public class PeriodicBindingUpdateBehavior : Behavior<DependencyObject>
{
public TimeSpan Interval { get; set; }
public DependencyProperty Property { get; set; }
public PeriodicBindingUpdateMode Mode { get; set; } = PeriodicBindingUpdateMode.UpdateTarget;
private WeakTimer timer;
private TimerCallback timerCallback;
protected override void OnAttached()
{
if (Interval == null) throw new ArgumentNullException(nameof(Interval));
if (Property == null) throw new ArgumentNullException(nameof(Property));
//Save a reference to the callback of the timer so this object will keep the timer alive but not vice versa.
timerCallback = s =>
{
try
{
switch (Mode)
{
case PeriodicBindingUpdateMode.UpdateTarget:
Dispatcher.Invoke(() => BindingOperations.GetBindingExpression(AssociatedObject, Property)?.UpdateTarget());
break;
case PeriodicBindingUpdateMode.UpdateSource:
Dispatcher.Invoke(() => BindingOperations.GetBindingExpression(AssociatedObject, Property)?.UpdateSource());
break;
}
}
catch (TaskCanceledException) { }//This exception will be thrown when application is shutting down.
};
timer = new WeakTimer(timerCallback, null, Interval, Interval);
base.OnAttached();
}
protected override void OnDetaching()
{
timer.Dispose();
timerCallback = null;
base.OnDetaching();
}
}
public enum PeriodicBindingUpdateMode
{
UpdateTarget, UpdateSource
}
/// <summary>
/// Wraps up a <see cref="System.Threading.Timer"/> with only a <see cref="WeakReference"/> to the callback so that the timer does not prevent GC from collecting the object that uses this timer.
/// Your object must hold a reference to the callback passed into this timer.
/// </summary>
public class WeakTimer : IDisposable
{
private Timer timer;
private WeakReference<TimerCallback> weakCallback;
public WeakTimer(TimerCallback callback)
{
timer = new Timer(OnTimerCallback);
weakCallback = new WeakReference<TimerCallback>(callback);
}
public WeakTimer(TimerCallback callback, object state, int dueTime, int period)
{
timer = new Timer(OnTimerCallback, state, dueTime, period);
weakCallback = new WeakReference<TimerCallback>(callback);
}
public WeakTimer(TimerCallback callback, object state, TimeSpan dueTime, TimeSpan period)
{
timer = new Timer(OnTimerCallback, state, dueTime, period);
weakCallback = new WeakReference<TimerCallback>(callback);
}
public WeakTimer(TimerCallback callback, object state, uint dueTime, uint period)
{
timer = new Timer(OnTimerCallback, state, dueTime, period);
weakCallback = new WeakReference<TimerCallback>(callback);
}
public WeakTimer(TimerCallback callback, object state, long dueTime, long period)
{
timer = new Timer(OnTimerCallback, state, dueTime, period);
weakCallback = new WeakReference<TimerCallback>(callback);
}
private void OnTimerCallback(object state)
{
if (weakCallback.TryGetTarget(out TimerCallback callback))
callback(state);
else
timer.Dispose();
}
public bool Change(int dueTime, int period)
{
return timer.Change(dueTime, period);
}
public bool Change(TimeSpan dueTime, TimeSpan period)
{
return timer.Change(dueTime, period);
}
public bool Change(uint dueTime, uint period)
{
return timer.Change(dueTime, period);
}
public bool Change(long dueTime, long period)
{
return timer.Change(dueTime, period);
}
public bool Dispose(WaitHandle notifyObject)
{
return timer.Dispose(notifyObject);
}
public void Dispose()
{
timer.Dispose();
}
}
}
我希望它本來能夠具有的元素(或結合),將拉這個週期性的,而不是具有基礎數據源通知。可以創建一個自定義綁定並添加一個`RefreshPeriod`屬性嗎?如果是這樣,那麼DispatcherTimer實例也可以被集中。 – 2010-07-02 04:33:13
事實上,我也有興趣純粹從XAML開始。我也沒有足夠的關於動畫atm的知識。 – buckley 2011-12-28 15:08:15