我试图使用异步等待根据复制操作更新我的WinForm上的进度条,但进度条只会在复制功能完成时更新,然后抛出一个无法更新的异常,因为它不是在同一个线程上？
虽然UI没有被阻止,但是看起来异步部分正在按预期工作,它只是与UI线程进行交互.
long fileProgress = 0;
long totalProgress = 0;
bool complete = false;
CopyFileEx.CopyFileCallbackAction callback(FileInfo source,FileInfo destination,object state,long totalFileSize,long totalBytesTransferred)
{
fileProgress = totalBytesTransferred;
totalProgress = totalFileSize;
return CopyFileEx.CopyFileCallbackAction.Continue;
}
async Task Progress()
{
await Task.Run(() =>
{
while (!complete)
{
if (fileProgress != 0 && totalProgress != 0)
{
fileProgressBar.Value = (int)(fileProgress / totalProgress) * 100;
}
}
});
}
private async void startButton_Click(object sender,EventArgs e)
{
Copy();
await Progress();
MessageBox.Show("Done");
}
void Copy()
{
Task.Run(() =>
{
CopyFileEx.FileRoutines.CopyFile(new FileInfo(@"C:\_USB\Fear.rar"),new FileInfo(@"H:\Fear.rar"),CopyFileEx.CopyFileOptions.All,callback,null);
complete = true;
});
}
解决方法
> async / await就是在处理I / O时没有阻塞线程 – 任何线程.在Task.Run()中放置一个阻塞I / O调用(就像你在Copy()中所做的那样)并没有避免阻塞 – 它只是创建了一个其他线程稍后会选择的任务,只是发现它本身被阻塞了它命中了阻塞的CopyFileEx.FileRoutines.CopyFile()方法.
@H_404_12@>您收到该错误是因为您没有正确使用async / await(无论上述情况如何).考虑哪个线程正在尝试修改UI对象fileProgressBar：随机线程池线程获取您在Task.Run()上创建的任务获取执行fileProgressBar.Value = …,这显然会抛出.
这是避免这种情况的一种方法：
async Task Progress()
{
await Task.Run(() =>
{
//A random threadpool thread executes the following:
while (!complete)
{
if (fileProgress != 0 && totalProgress != 0)
{
//Here you signal the UI thread to execute the action:
fileProgressBar.Invoke(() =>
{
//This is done by the UI thread:
fileProgressBar.Value = (int)(fileProgress / totalProgress) * 100
});
}
}
});
}
private async void startButton_Click(object sender,EventArgs e)
{
await Copy();
await Progress();
MessageBox.Show("Done"); //here we're on the UI thread.
}
async Task Copy()
{
//You need find an async API for file copy,and System.IO has a lot to offer.
//Also,there is no reason to create a Task for MyAsyncFileCopyMethod - the UI
// will not wait (blocked) for the operation to complete if you use await:
await MyAsyncFileCopyMethod();
complete = true;
}
