WPF使用命令减慢更新UI控件

Question

我通过命令属性将命令绑定到按钮,并在放置的页面中执行命令绑定.在execute方法中,我创建一个包含后台worker的类的实例,然后启动它(这是一个很长的任务).后台worker(bw)类包含一个变量isRunning,它在执行DoWork方法之前设置为true,在执行RunWorkerCompleted时设置为false.因此,从放置按钮的页面后面的代码,在CanExecute方法中,如果bw没有运行(isRunning = false),则将e.canExecute设置为true,如果isRunning = true,则将e.canExecute设置为false.

当我按下按钮时,它会长时间启动bw进程并且该按钮被禁用.确定这是正确的,但是当后台工作人员(bw)完成时,按钮不会返回启用,直到我再次按下它.当它被禁用时我按下(当bw完成时)它被启用.为什么按钮没有自动返回到bw结束时启用？

我的代码片段:

<Page  x:Class="GParts.Pages.MyPage" 
  xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
   xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"       
   xmlns:Microsoft_Windows_Themes="clr-namespace:Microsoft.Windows.Themes;
    assembly=PresentationFramework.Aero"            
    xmlns:local="clr-namespace:GParts"      
    Loaded="Page_Loaded"  
    Unloaded="Page_Unloaded" 
    Height="Auto">

  <Page.CommandBindings>
    <CommandBinding Command="{x:Static local:Pages.MyPage.rcmd}"
               Executed="CommandBinding_Executed"
               CanExecute="CommandBinding_CanExecute"/>
  </Page.CommandBindings>

   <...>
   <Button Command="{x:Static local:Pages.MyPage.rcmd}" />

<...>
</Page>

页面背后的代码:

 namespace GParts.Pages
 {

   public partial class MyPage : Page
   {

    public static RoutedCommand rcmd = new RoutedCommand();

    private cBgWorker bw;

    <...>

    // ExecutedRoutedEventHandler for the custom button remove all command.
    private void CommandBinding_Executed(object sender, ExecutedRoutedEventArgs e)
    {

            // get an isntance of the background worker class
            bw = new cBgWorker();

            // start the long task
            bw.StartTask();

    }

    // CanExecuteRoutedEventHandler for the custom button remove all command.
    private void CommandBinding_CanExecute(object sender, CanExecuteRoutedEventArgs e)
    {
        // bw is the instance of background worker class
        if (bw == null)
        {
            e.CanExecute = true;
        }
        else
        {
            e.CanExecute = !bw.isRunning;// isRunning indicates if bw is
                                         //executing now         
        }
    }

    <...>

} // end class
} // end namespace

Answer 1

当BackgroundWorker完成后,请致电 CommandManager.InvalidateRequerySuggested();

默认情况下,命令仅偶尔由WPF重新获取.否则,在每次ICommand实现时不断调用"CanExecute"会产生大量开销.调用上述方法会强制CommandManager立即更新.

这将强制命令适当地重新启用/禁用.