使用Thread.sleep使UI线程等待

Question

I have written this code in C# for WP7 :

public void btn_handler(object sender, EventArgs args)
    {
        Button btn_Pressed = (Button)sender;
        ImageBrush br = new ImageBrush();
        br.ImageSource = new BitmapImage(new Uri("/images/cat.png"
                                                 , UriKind.Relative));

        btn_Pressed.Background = br;

        Thread.Sleep(5000);

       SolidColorBrush sBrush = new SolidColorBrush(); 
       sBrush.Color = System.Windows.Media.Colors.White;
       btn_Pressed.Background = sBrush;            
    }

Whenever the user clicks the button, I want the background of the button to change to an image. After about 5 secs, I want the background to change back to White. Currently, the program doesnt change the background image of the button, it waits for 5 secs and directly changes the background to White.

I am a noob to WP. I tried searching for a solution and what I got was to create a DispatcherThread but I didnt understand how to proceed. Please help :(

Answer 1

You current approach is incorrect. It is keeping the UI thready busy. It updates the UI when it gets free.

Here is what is happening

Button Gets click. UI thread change the button background to Images. Then it sleeps for 5 secs and then it changes the background to white. Note that UI thread is still busy. It will only update the actual UI when it will be free. Once it has changed back color to white it gets free and updates the UI and you see the change on screen.

You need to do this

 //inside the button click event create a background worker
 BackgroundWorker worker = new BackgroundWorker();
 worker.RunWorkerCompleted += new 

 RunWorkerCompletedEventHandler(worker_RunWorkerCompleted);
 worker.DoWork += new DoWorkEventHandler(worker_DoWork);
 worker.RunWorkerAsync();

 Button btn_Pressed = (Button)sender;
 ImageBrush br = new ImageBrush();
 br.ImageSource = new BitmapImage(new Uri("/images/cat.png", UriKind.Relative));

 btn_Pressed.Background = br;


 public static void worker_RunWorkerCompleted(object sender, 
                                              RunWorkerCompletedEventArgs e)
    {
    //once backgroudn work i.e. DoWork is complete this method will be 
    //called and code below will execute in UI thread
    SolidColorBrush sBrush = new SolidColorBrush(); 
    sBrush.Color = System.Windows.Media.Colors.White;
    btn_Pressed.Background = sBrush;  
    }

 public  static  void worker_DoWork(object sender, DoWorkEventArgs e)
    {
    //it will wait 5 secs in the background thread
    Thread.Sleep(5000);
    }

Answer 2

You should never ever block the UI thread by calling Thread.Sleep .

I think that the best solution is to create a storyboard in your XAML that will perform the required visual changes. Your button click event handler should then simply call Begin on the storyboard.