Nasıl Yapılır: PriorityBinding Uygulama
PriorityBinding in Windows Presentation Foundation (WPF) works by specifying a list of bindings. The list of bindings is ordered from highest priority to lowest priority. If the highest priority binding returns a value successfully when it is processed then there is never a need to process the other bindings in the list. It could be the case that the highest priority binding takes a long time to be evaluated, the next highest priority that returns a value successfully will be used until a binding of a higher priority returns a value successfully.
Örnek
To demonstrate how PriorityBinding works, the AsyncDataSource object has been created with the following three properties: FastDP, SlowerDP, and SlowestDP.
The get accessor of FastDP returns the value of the _fastDP data member.
The get accessor of SlowerDP waits for 3 seconds before returning the value of the _slowerDP data member.
The get accessor of SlowestDP waits for 5 seconds before returning the value of the _slowestDP data member.
.gif "Not") Not |
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This example is for demonstration purposes only.The Microsoft .NET guidelines recommend against defining properties that are orders of magnitude slower than a field set would be.For more information, see Özellikler ve Yöntemler arasında seçim yapma. |
Public Class AsyncDataSource
' Properties
Public Property FastDP As String
Get
Return Me._fastDP
End Get
Set(ByVal value As String)
Me._fastDP = value
End Set
End Property
Public Property SlowerDP As String
Get
Thread.Sleep(3000)
Return Me._slowerDP
End Get
Set(ByVal value As String)
Me._slowerDP = value
End Set
End Property
Public Property SlowestDP As String
Get
Thread.Sleep(5000)
Return Me._slowestDP
End Get
Set(ByVal value As String)
Me._slowestDP = value
End Set
End Property
' Fields
Private _fastDP As String
Private _slowerDP As String
Private _slowestDP As String
End Class
public class AsyncDataSource
{
private string _fastDP;
private string _slowerDP;
private string _slowestDP;
public AsyncDataSource()
{
}
public string FastDP
{
get { return _fastDP; }
set { _fastDP = value; }
}
public string SlowerDP
{
get
{
// This simulates a lengthy time before the
// data being bound to is actualy available.
Thread.Sleep(3000);
return _slowerDP;
}
set { _slowerDP = value; }
}
public string SlowestDP
{
get
{
// This simulates a lengthy time before the
// data being bound to is actualy available.
Thread.Sleep(5000);
return _slowestDP;
}
set { _slowestDP = value; }
}
}
The Text property binds to the above AsyncDS using PriorityBinding:
<Window.Resources>
<c:AsyncDataSource SlowestDP="Slowest Value" SlowerDP="Slower Value"
FastDP="Fast Value" x:Key="AsyncDS" />
</Window.Resources>
<StackPanel HorizontalAlignment="Center" VerticalAlignment="Center"
DataContext="{Binding Source={StaticResource AsyncDS}}">
<TextBlock FontSize="18" FontWeight="Bold" Margin="10"
HorizontalAlignment="Center">Priority Binding</TextBlock>
<TextBlock Background="Honeydew" Width="100" HorizontalAlignment="Center">
<TextBlock.Text>
<PriorityBinding FallbackValue="defaultvalue">
<Binding Path="SlowestDP" IsAsync="True"/>
<Binding Path="SlowerDP" IsAsync="True"/>
<Binding Path="FastDP" />
</PriorityBinding>
</TextBlock.Text>
</TextBlock>
</StackPanel>
When the binding engine processes the Binding objects, it starts with the first Binding, which is bound to the SlowestDP property. When this Binding is processed, it does not return a value successfully because it is sleeping for 5 seconds, so the next Binding element is processed. The next Binding does not return a value successfully because it is sleeping for 3 seconds. The binding engine then moves onto the next Binding element, which is bound to the FastDP property. This Binding returns the value "Fast Value". The TextBlock now displays the value "Fast Value".
After 3 seconds elapses, the SlowerDP property returns the value "Slower Value". The TextBlock then displays the value "Slower Value".
After 5 seconds elapses, the SlowestDP property returns the value "Slowest Value". That binding has the highest priority because it is listed first. The TextBlock now displays the value "Slowest Value".
See PriorityBinding for information about what is considered a successful return value from a binding.