Question

如何在Async Task类中传递上下文，该类在Main Activity的不同java文件中编码但是从主活动调用？

以下是我的代码：

 @Override

protected void onPostExecute(List<Movie_ModelClass> result) {
        super.onPostExecute(result);

        if (result != null) {
            Movie_Adapter movieAdapter = new Movie_Adapter(new MainActivity().getApplicationContext() , R.layout.custom_row, result);
            MainActivity ovj_main = new MainActivity();
            ovj_main.lv_main.setAdapter(movieAdapter);
        } else {
            Toast.makeText(new MainActivity().getApplicationContext() ,"No Data Found", Toast.LENGTH_LONG);

        }
        if (progressDialog.isShowing()) {
            progressDialog.dismiss();
    }

Answer 1

您可以将Context实例作为构造函数参数传递（并保留WeakReference以避免内存泄漏。）

例如：

public class ExampleAsyncTask extends AsyncTask {
    private WeakReference<Context> contextRef;

    public ExampleAsyncTask(Context context) {
        contextRef = new WeakReference<>(context);
    }

    @Override
    protected Object doInBackground(Object[] params) {
        // ...
    }

    @Override
    protected void onPostExecute(Object result) {
        Context context = contextRef.get();
        if (context != null) {
            // do whatever you'd like with context
        }
    }
}

执行：

new ExampleAsyncTask(aContextInstance).execute();

Answer 2

您只需在AsyncTask的构造函数中传递上下文。

<强> MyAsyncTask.java

public class MyAsyncTask extends AsyncTask<Void, Integer, List> {

    private final Context mContext;

    public MyAsyncTask(final Context context) {
         mContext = context;
    }
}

然后只需在onPostExecute（）方法中使用mContext变量。

当您从MainActivity调用AsyncTask时，将上下文传递给MyAsyncTask的构造函数。

<强> MainActivity.java

final MyAsyncTask task = new MyAsyncTask(getApplicationContext());
task.execute();

Answer 3

在尝试使用Async类压缩图像时遇到了相同的问题。我有一个构造函数，所以我只添加了以下内容

   public BackgroundImageResize(Context context, Bitmap bm) {
    if (bm != null){
        mBitmap = bm;
    }
    this.context =context;
}

然后我像下面这样叫课，

公共无效的uploadDevicePhoto（Uri imageUri）{

BackgroundImageResize resize = new BackgroundImageResize(this,null);
resize.execute(imageUri);

}

如何将Context传递给AsyncTask？

3 个答案: