如何通过 AsyncTask 正确使用 Intent 和 Uri 数据

Question

我需要使用 AsyncTask 从 Web 下载图像。我想使用可以返回到我的 MainActivity 的意图来执行此操作。下面的代码确实下载了图像，但是我必须按一次后退按钮才能真正看到图像。我传入的 Uri 是下载方法正常工作所需的数据。

这是我的问题：如何将 Uri 传递到 AsyncTask，正确形成启动下载方法的意图，然后 return 以该意图调用 activity？

另外请不要提Picasso，我特别需要用到AsyncTask

   private class DownloadAsyncTask extends AsyncTask<Uri, Void, Intent>{

    private Uri  mUri;

    public DownloadAsyncTask(Uri uri) {

        this.mUri = uri;
    }

    @Override
    protected void onPreExecute() {

        Toast.makeText(DownloadActivity.this, "Beginning download...", Toast.LENGTH_SHORT).show();
    };

    @Override
    protected Intent doInBackground(Uri... params) {

        Log.i(TAG, "in doInBackground()");
        Intent i = new Intent(DownloadActivity.this, MainActivity.class);
        //set the intent data to the result of the method that actually downloads this image
        i.setData(DownloadTools.downloadImage(DownloadActivity.this, mUri));
        setResult(RESULT_OK, i);

        return i;
    }

    protected void onPostExecute() {

        Toast.makeText(DownloadImageActivity.this, "Finished Download.", Toast.LENGTH_SHORT).show();

        finish();
    };
}

MainActivity 回调：

    @Override
protected void onActivityResult(int requestCode,
                                int resultCode,
    if (resultCode == RESULT_OK) {
        if (requestCode == DOWNLOAD_IMAGE_REQUEST) {

            //use the path found in the data to open the image in the gallery.
            String address = data.getData().toString();
            Intent galleryIntent = makeGalleryIntent(address);

            // Start the Gallery Activity.
            startActivity(galleryIntent);
        }
    }

Answer 1

您为什么尝试使用意图来执行此方法？据我了解，您想启动 AynTask 并将结果传回主要活动，不是吗？为此，您应该使用和接口来实现回调。

public interface I_CallBackTask {

public void getResultFromAsynTask(String result);

}

private class DownloadAsyncTask extends AsyncTask<Uri, Void, String>{



private Uri  mUri;
public I_CallBackTask callback;

public DownloadAsyncTask(Uri uri) {

    this.mUri = uri;
}

@Override
protected void onPreExecute() {

    Toast.makeText(DownloadActivity.this, "Beginning download...", Toast.LENGTH_SHORT).show();
};

@Override
protected String doInBackground(Uri... params) {

    //Do your background code for download here

    //return the result of your download: if is an image it could be byte[], ...


    return resultfrombackground;
}
//result same type as resultfrombackground

protected void onPostExecute(String result) {

    callback.getResultFromAsynTask(result);


};
}

//your main activity

public YourActivity implements CallBackTask{
// your Activity 


 //your code .....


//On your main activity start the asyntask and pass your uri in the parameter
DownloadAsyncTask asyntask = new DownloadAsyncTask(yourUri);
asyncTask.execute();
asyncTask.callback = this;



 @Override
public void getResultFromAsynTask(String result){
// do what you need with the result and start the new activity
}


}

如何通过 AsyncTask 正确使用 Intent 和 Uri 数据

How to properly use Intent and Uri data with AsyncTask

android

android-intent

android-asynctask

uri