即使使用线程池，Android Cordova 插件也会锁定 UI 线程

Question

我已经编写了一个 Cordova 插件，可以在 Android 上调整图像大小，但是在翻动大量图像(超过 100 张)时 UI 会锁定，直到翻动停止。我正在对 theadPool 执行所有的大小调整，最初只有一个可运行的，但在阅读了这篇关于 Cordova Plugins and Thread Blocking 的博客文章之后我改用外部类(class)来完成这项工作。但是我仍然得到:

W/PluginManager﹕ THREAD WARNING: exec() call to ImageStore.getImage blocked the main thread for 91ms. Plugin should use CordovaInterface.getThreadPool().

对于每个调整大小的图像，调用如下所示:

private boolean getImage(final JSONArray args, final CallbackContext callbackContext) throws JSONException {

    JSONObject argObject = args.getJSONObject(0);

    int photoId = argObject.getInt("photoId");
    final PhotoData photoData = mPhotos.get(photoId);

    cordova.getThreadPool().execute(new GetImageRunnable(photoData, callbackContext));

    return true;
}

除了传入的 photoData 对象，GetImageRunnable 没有指向主插件的链接。有什么方法可以查看导致速度变慢或阻塞主线程的原因吗？

Answer 1

你可以试试下面的代码，它使用了最小的 AsyncTask运行 GetImageRunnable:

private boolean getImage(final JSONArray args, final CallbackContext callbackContext) throws JSONException {

    JSONObject argObject = args.getJSONObject(0);

    int photoId = argObject.getInt("photoId");
    final PhotoData photoData = mPhotos.get(photoId);

    (new MyTask(photoData, callbackContext)).execute();

    return true;
}

private class MyTask extends AsyncTask<Void, Void, Void> {

    private PhotoData mPhotoData;
    private CallbackContext mCallbackContext;

    public MyTask(PhotoData photoData, CallbackContext callbackContext) {
        mPhotoData = photoData
        mCallbackContext = callbackContext;
    }

    protected Void doInBackground(Void... v) {
        (new GetImageRunnable(photoData, callbackContext)).run();
        return null;
    }

    protected void onProgressUpdate(Void... v) {
    }

    protected void onPostExecute(Void v) {
    }
}

不过，它还有一些不足之处；回调将在后台线程中运行。如果你需要它在主线程中运行，你可以屏蔽初始的CallbackContext(它不是最终的)，并将结果传递给原始的onPostExecute :

private boolean getImage(final JSONArray args, final CallbackContext callbackContext) throws JSONException {

    JSONObject argObject = args.getJSONObject(0);

    int photoId = argObject.getInt("photoId");
    final PhotoData photoData = mPhotos.get(photoId);

    (new MyTask(photoData, callbackContext)).execute();

    return true;
}

private class MyTask extends AsyncTask<Void, Void, Void> {

    private PhotoData mPhotoData;
    private CallbackContext mCallbackContext;
    private CallbackContext mMaskedContext;

    public MyTask(PhotoData photoData, CallbackContext callbackContext) {
        mPhotoData = photoData
        mCallbackContext = callbackContext;
        mMaskedContext = new MyCallbackContext(callbackContext);
    }

    protected Void doInBackground(Void... v) {
        (new GetImageRunnable(photoData, mMaskedContext)).run();
        return null;
    }

    protected void onProgressUpdate(Void... v) {
    }

    protected void onPostExecute(Void v) {
        mCallbackContext.sendPluginResult(mMaskedContext.getPluginResult());
    }
}

class MyCallbackContext extends CallbackContext {
    private CallbackContext mOriginalContext;
    private PluginResult mPluginResult;

    public MyCallbackContext(CallbackContext originalContext) {
        super(originalContext.getCallbackId(), null);
        mOriginalContext = originalContext;
    }

    public void sendPluginResult(PluginResult pluginResult) {
        mPluginResult = pluginResult;
    }

    public pluginResult getPluginResult() {
        return mPluginResult;
    }
}

注意:这没有经过测试，代码只是为了说明想法。