Xamarin Android 在异步函数中关闭 ProgressDialog

Question

我有一个异步函数，我想在任务完成后关闭 ProgressDialog。我看到它是在 onPostExecute 方法中完成的，但是我没有异步类来实现它。就我而言，它是异步方法

    public async void ScanBarcode()
    {
        dialogIndicator.Show ();

        var zscanner = new MobileBarcodeScanner();
        //var result = await zscanner.Scan();

        var result = await zscanner.Scan ();

        HandleScanResult(result);


    }
    void HandleScanResult(ZXing.Result result)
    {
       dialogIndicator.Dismiss ();
    }

App 为 dialogIndicator.Dismiss (); 抛出异常。我明白了

  "Android.Util.AndroidRuntimeException: Only the original thread that created a view hierarchy can touch its views.

  at --- End of managed exception stack trace ---
  at android.view.ViewRootImpl$CalledFromWrongThreadException: Only    the original thread that created a view hierarchy can touch its views.
  at at android.view.ViewRootImpl.checkThread(ViewRootImpl.java:7155)
  at at android.view.ViewRootImpl.doDie(ViewRootImpl.java:6255)
  at at android.view.ViewRootImpl.die(ViewRootImpl.java:6240)
  at at    android.view.WindowManagerGlobal.removeViewLocked(WindowManagerGlobal.java:365)
  at at android.view.WindowManagerGlobal.removeView(WindowManagerGlobal.java:320)
  at at android.view.WindowManagerImpl.removeViewImmediate(WindowManagerImpl.java:84)
  at at android.app.Dialog.dismissDialog(Dialog.java:420)
  at at android.app.Dialog$1.run(Dialog.java:128)
  at at android.os.Handler.handleCallback(Handler.java:733)
  at at android.os.Handler.dispatchMessage(Handler.java:95)
  at at android.os.Looper.loop(Looper.java:146)
  at at android.app.ActivityThread.main(ActivityThread.java:5731)
  at at java.lang.reflect.Method.invokeNative(Native Method)
  at at java.lang.reflect.Method.invoke(Method.java:515)
  at at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1291)
  at at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1107)

at at dalvik.system.NativeStart.main(Native Method)

在这种情况下如何关闭 ProgressDialog。

Answer 1

知道抛出什么类型的异常以查看发生了什么问题会很有用。

我建议您更改代码中的某些内容。

首先，将async 与void 返回类型一起使用不是最佳做法。因为这使得无法等待ScanBarcode 或从那里捕获任何异常。

第二件事是你没有在HandleScanResult 内做任何在ScanBarcode 内不能做的事情。因此，我将其合并为以下内容：

public async Task ScanBarcode()
{
    dialogIndicator.Show ();

    var zscanner = new MobileBarcodeScanner();
    var result = await zscanner.Scan ();

    dialogIndicator.Dismiss ();
}

这样，代码“等待”扫描结果，然后继续关闭 dialogIndicator。

如果您从 UI 线程以外的另一个线程调用 ScanBarcode，您可以像这样在 UI 线程上强制执行：

public async Task ScanBarcode()
{
    RunOnUiThread(()=>
    {
        dialogIndicator.Show ();
    });

    var zscanner = new MobileBarcodeScanner();
    var result = await zscanner.Scan ();

    RunOnUiThread(()=>
    {
        dialogIndicator.Dismiss ();
    });
}