java 如何将上下文传递给 AsyncTask？
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How to pass Context to AsyncTask?
提问by Darshan Dhoriya
How to pass context in Async Taskclass which is coded in different java file from Main Activitybut it called from main activity?
如何在Async Task类中传递上下文，该类是在不同的 java 文件中编码的，Main Activity但它是从主活动调用的？
Below is my code:
下面是我的代码：
@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();
}
回答by earthw0rmjim
You could just pass a Contextinstance as a constructor parameter (and keep a WeakReferenceto it to avoid memory leaks).
您可以将一个Context实例作为构造函数参数传递（并保留WeakReference它以避免内存泄漏）。
For example:
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
}
}
}
And the execution:
和执行：
new ExampleAsyncTask(aContextInstance).execute();
回答by Tristan
You can just pass the context in the constructor of your AsyncTask.
您可以在 AsyncTask 的构造函数中传递上下文。
MyAsyncTask.java
我的异步任务.java
public class MyAsyncTask extends AsyncTask<Void, Integer, List> {
private final Context mContext;
public MyAsyncTask(final Context context) {
mContext = context;
}
}
and then just use the mContext variable in your onPostExecute() method.
然后在您的 onPostExecute() 方法中使用 mContext 变量。
When you call your AsyncTask from your MainActivity, you pass the context to the constructor of MyAsyncTask.
当您从 MainActivity 调用 AsyncTask 时，会将上下文传递给 MyAsyncTask 的构造函数。
MainActivity.java
主活动.java
final MyAsyncTask task = new MyAsyncTask(getApplicationContext());
task.execute();
回答by Hymanson
I encountered same issue when trying to compress an image using an Async class. I had a constructor in place so I just added context as below
我在尝试使用 Async 类压缩图像时遇到了同样的问题。我有一个构造函数，所以我只是添加了如下上下文
public BackgroundImageResize(Context context, Bitmap bm) {
if (bm != null){
mBitmap = bm;
}
this.context =context;
}
Then i called the class like below,
然后我像下面这样打电话给班级，
public void uploadDevicePhoto(Uri imageUri){
public void uploadDevicePhoto(Uri imageUri){
BackgroundImageResize resize = new BackgroundImageResize(this,null);
resize.execute(imageUri);
}
}
