David CoulterandAndy De George
674b773578
* Links: .NET Desktop - framework\wpf * Apply suggestions from code review Co-authored-by: Andy De George <[email protected]>
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title, ms.date, dev_langs, helpviewer_keywords, ms.assetid
| title | ms.date | dev_langs | helpviewer_keywords | ms.assetid | |||
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| How to: Implement PriorityBinding | 03/30/2017 |
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d63b65ab-b3e9-4322-9aa8-1450f8d89532 |
How to: Implement PriorityBinding
xref:System.Windows.Data.PriorityBinding in [!INCLUDETLA#tla_winclient] 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.
Example
To demonstrate how xref:System.Windows.Data.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.
Note
This example is for demonstration purposes only. The .NET guidelines recommend against defining properties that are orders of magnitude slower than a field set would be. For more information, see Choosing Between Properties and Methods.
[!code-csharpPriorityBinding#1] [!code-vbPriorityBinding#1]
The xref:System.Windows.Controls.TextBlock.Text%2A property binds to the above AsyncDS using xref:System.Windows.Data.PriorityBinding:
[!code-xamlPriorityBinding#2]
When the binding engine processes the xref:System.Windows.Data.Binding objects, it starts with the first xref:System.Windows.Data.Binding, which is bound to the SlowestDP property. When this xref:System.Windows.Data.Binding is processed, it does not return a value successfully because it is sleeping for 5 seconds, so the next xref:System.Windows.Data.Binding element is processed. The next xref:System.Windows.Data.Binding does not return a value successfully because it is sleeping for 3 seconds. The binding engine then moves onto the next xref:System.Windows.Data.Binding element, which is bound to the FastDP property. This xref:System.Windows.Data.Binding returns the value "Fast Value". The xref:System.Windows.Controls.TextBlock now displays the value "Fast Value".
After 3 seconds elapses, the SlowerDP property returns the value "Slower Value". The xref:System.Windows.Controls.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 xref:System.Windows.Controls.TextBlock now displays the value "Slowest Value".
See xref:System.Windows.Data.PriorityBinding for information about what is considered a successful return value from a binding.