Silverlight跨线程UI更新问题

Question

我有这个类：

public class UploadFile : INotifyPropertyChanged {
    private string name;
    public string Name {
        get {
            return name;
        }
        set {
            name = value;
            OnPropertyChanged("Name");
        } 
    }

    private FileInfo fileInfo;
    public FileInfo FileInfo { get; set; }

    private string length;
    public string Length {
        get {
            return length;
        }
        set {
            length = value;
            OnPropertyChanged("Length");
        }  
    }

    private int percentage;
    public int Percentage {
        get {
            return percentage;
        }
        set {
            percentage = value;
            OnPropertyChanged("Percentage");
        } 
    }

    public string ProgressValue {
        get { return string.Format("{0}%", Percentage); }
    }

    private string imageSource;
    public string ImageSource {
        get {
            return imageSource;
        }
        set {
            imageSource = value;
            OnPropertyChanged("ImageSource");
        }  
    }


    #region INotifyPropertyChanged Members

    public event PropertyChangedEventHandler PropertyChanged;

    #endregion

    private void OnPropertyChanged(string property) {
        if (PropertyChanged != null) {
            PropertyChanged(this, new PropertyChangedEventArgs(property));
        }
    }
}

我正在尝试创建一个能够上传大文件和多个文件的文件上传功能。我使用了一个Web服务来实现这个功能。我已经在我的用户界面中进行了双向绑定，现在我想要上传这些文件。我将使用以下代码来实现：

private void DoUpload() {
        foreach (UploadFile file in fileInfos){
            int BUFFERSIZE = 1024;
            int offset = 0; //get from webservice, when partial file
            FileStream s = file.FileInfo.OpenRead();
            byte[] buffer = null;
            long remainingBytes = s.Length - offset;
            while (remainingBytes > 0) {
                if (remainingBytes < BUFFERSIZE) {
                    buffer = new byte[remainingBytes];
                    BUFFERSIZE = (int)remainingBytes;
                }
                else if (remainingBytes > BUFFERSIZE) {
                    buffer = new byte[BUFFERSIZE];
                }

                s.Read(buffer, 0, BUFFERSIZE);
                //push to webservice
                Thread.Sleep(20);
                //UploadService.Service1SoapClient client = new MultiLargeFileUpload.UploadService.Service1SoapClient();
                //client.LargeUploadCompleted +=new EventHandler<AsyncCompletedEventArgs>(client_LargeUploadCompleted);
                //client.LargeUploadAsync(1, buffer, file.Name);
                offset += BUFFERSIZE;
                int newPercentage = offset / (int)file.FileInfo.Length * 100;
                file.Percentage = newPercentage;
                remainingBytes = s.Length - offset;                    
            }
            //file.Percentage = 100;
            //file.ImageSource = "accept.png";
        }
    }

问题在于我无法更新UI，或者说跨线程操作。我尝试使用了Dispatcher，但是并没有成功，因为我不知道在哪里插入它。

- H4mm3rHead

Answer 1

我猜你正在尝试更新你的用户界面。

           file.Percentage = newPercentage;
           remainingBytes = s.Length - offset;

你需要将这个操作包装在一个委托中，并在另一个线程上使用Dispatcher.BeginInvoke()方法更新你的UI：

Dispatcher.BeginInvoke(()=>{
    file.Percentage=newPercentage;
    remainingBytes = s.Length - offset;
});

通过这种方式，您可以向主线程的消息队列发送一条消息，主线程在有时间时可以执行委托。

- Jan Jongboom