從BackgroundWorker返回一個對象

Question

我抖動BackgroundWorker線程中的圖像，並且需要在完成圖像處理後更新UI。我需要更新的圖像與DitherWorker存在於同一個類中。如何傳遞BitmapSource以避免發生指出的錯誤？

public void DitherWorker() 
{ 
    double scalebox = Double.Parse(myWindow.scaleBox.Text); 
    int slider = (int)myWindow.convolutionBiasSlider.Value; 
    BitmapSource final = null; 
    ditherobj output = new ditherobj(scalebox, originalImage, slider);//.Get_Halftone(); 

    worker = new BackgroundWorker(); 
    worker.WorkerSupportsCancellation = true; 

    worker.DoWork += delegate(object s, System.ComponentModel.DoWorkEventArgs args) 
    { 
     ditherobj dob = (ditherobj)args.Argument; 
     Binarize bn = new Binarize(dob.scalebox, dob.localbms, dob.slider); 
     BitmapSource bms = (BitmapSource)bn.Get_Halftone(); 
     final = bms; 
     args.Result = new ditherobj(0,null,0,bms); 
    }; 

    worker.RunWorkerCompleted += delegate(object s, RunWorkerCompletedEventArgs args) 
    { 
     ditherobj dob = (ditherobj)args.Result; 
     image1.Source = dob.localbms; //ERROR. The calling thread cannot access this object because another thread owns it 

     myWindow.Dispatcher.Invoke(DispatcherPriority.Normal, new ThreadStart(() => 
     { 
      myWindow.activityBar.IsBusy = false; 
     })); 
    }; 

    worker.RunWorkerAsync((ditherobj)output); 
} 

public class ditherobj 
    { 
     public double scalebox; 
     public BitmapSource localbms; 
     public BitmapImage localbmi; 
     public int slider; 

     public ditherobj(double scalebox, BitmapImage localbmi, int slider, BitmapSource bms = null) 
     { 
      this.scalebox = scalebox; 
      this.slider = slider; 
      if (bms == null) 
      { 
       BitmapImage test = localbmi.Clone(); 
       localbms = (BitmapSource)test; 
      } 
      else 
       localbms = bms; 
     } 
    } 

問題解決了。在傳遞之前，BitmapSource必須在後臺線程中凍結。下面是最終comented代碼：

BackgroundWorker worker; 
    public void DitherWorker() 
    { 
     double scalebox = Double.Parse(myWindow.scaleBox.Text); //get values from UI for the job 
     int slider = (int)myWindow.convolutionBiasSlider.Value; 
     DitherSettings output = new DitherSettings(scalebox, originalImage, slider); //create holder object to be passed to BackgroundWorker 
     worker = new BackgroundWorker(); 

     worker.DoWork += delegate(object s, System.ComponentModel.DoWorkEventArgs args) 
     { 

      DitherSettings ds = (DitherSettings)args.Argument; //cast argument as our holder object 
      Binarize bn = new Binarize(ds.scalebox, ds.localbms, ds.slider); //create object to do our work 
      BitmapSource bms = (BitmapSource)bn.Get_Halftone(); //do work 
      bms.Freeze(); //freeze resulting BitmapSource so it can be utilized elsewhere 
      args.Result = new DitherSettings(0,null,0,bms); //create new object with resulting BitmapSource 

     }; 

     worker.RunWorkerCompleted += delegate(object s, RunWorkerCompletedEventArgs args) 
     { 
      DitherSettings ds = (DitherSettings)args.Result; //get object with our BitmapSource 

      if (image1.Dispatcher.CheckAccess()) 
       this.image1.Source = ds.localbms; //update class image 

      myWindow.Dispatcher.Invoke(DispatcherPriority.Normal, new ThreadStart(() => 
      { 
       myWindow.activityBar.IsBusy = false; //Update UI control 
      })); 
     }; 

     worker.RunWorkerAsync((DitherSettings)output); 

    } 

    public class DitherSettings 
    { 
     public double scalebox; 
     public BitmapSource localbms; 
     public BitmapImage localbmi; 
     public int slider; 

     public DitherSettings(double scalebox, BitmapImage localbmi, int slider, BitmapSource bms = null) 
     { 
      this.scalebox = scalebox; 
      this.slider = slider; 
      if (bms == null) 
       localbms = (BitmapSource)localbmi; 
      else 
       localbms = bms; 
     } 
    } 

Answer 1

呼籲BitmapSource的Freeze()功能，當你仍然在後臺線程。

這使得對象不可變，因此可以在主線程上使用。

Learn here more about freezable wpf objects.該頁面討論了Freezables的許多其他方面，但它也明確指出：「凍結的Freezable也可以跨線程共享......」。在WPF中構建的在後臺線程上構建GUI元素（比如位圖）的功能是如果你問我，那麼就是＃1 underadvertized WPF功能。

Answer 2

BitmapSource.Clone()如果您想複製對象，可能會有一些用處。

Dispatcher.CheckAccess()應該在設置image1之前調用。