Android "Back Button" causes javascript to stop

Question

I'm developing an app with a webview. I have a fileupload element and my app enables choosing "camera" or "gallery" by displaying an AlertDialog in the "openfilechooser" method. Here is what i'm doing:

-I tap on the fileupload element
-An AlertDialog pops up to read my choice of "camera" or "gallery"
-I change my mind and give up choosing a file and click "Android Back Button"

When i click the back button, all javascript stops and my page stops responding.

Is there a reason for javascript to stop? Thanks in advance

Answer 1

I tried several tricks and finally found the solution.

FileUpload element needs a "ValueCallback" after all these method calls.So "onActivityResult" has to return a result to the fileupload element. But the "onActivityResult" method can not be called when user cancels the alert dialog. This causes fileupload element to generate error.

I added "setOnCancelListener" to my alert dialog like this:

.setOnCancelListener(new DialogInterface.OnCancelListener() {

    @Override
    public void onCancel(DialogInterface dialog) {
     mUploadMessage.onReceiveValue(null);
     mUploadMessage = null;
    }
})

You have to return at least "null" to the file upload element in order to keep operating . Otherwise fileupload stalls and this causes all javascript to stall.

I also catched another case that makes fileupload stall:
- User taps on the fileupload element
- Chooses a choice (Cam or Galller doesn't matter)
- Cam or Gallery shows up and user presses the "Back Button"

This returns a RESULT_CANCELED code to the "onActivityResult" method and you have to handle it like this:

@Override
protected void onActivityResult(int requestCode, int resultCode,
        Intent intent) {
    try {
        super.onActivityResult(requestCode, resultCode, intent);

        if (requestCode == CAMERA_REQUEST && resultCode == RESULT_OK
                && intent != null)
            mUploadMessage.onReceiveValue(intent.getData());
        else
            mUploadMessage.onReceiveValue(null);
    } catch (Exception e) {
        Log.e("Error", e.getLocalizedMessage());
        mUploadMessage.onReceiveValue(null);
    } finally {
        mUploadMessage = null;
    }
}

mUploadMessage is defined like this:

    private ValueCallback<Uri> mUploadMessage;