如何使用AsyncTask分配全局变量

Question

Here I've given a small example of the problem I'm facing with global variables and AsyncTasks. I've gone and read in data from a file and assigned that data to a string and in the onPostExecute() method I assigned that string to the global variable. However when I assign the TextView with the "aString" variable, the output is still "nothing".

I know that if you do the TextView assigning in the onPostExecute() method it works however what if I want to use the data in methods outside of the AsyncTask.

Can someone please help with this, I think I'm not getting something?

public class GoodAsync extends Activity{

    TextView tv;
    String aString = "nothing";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        // TODO Auto-generated method stub
        super.onCreate(savedInstanceState);
        setContentView(R.layout.asynctasks);

        new AsyncTasker().execute();

        tv = (TextView) findViewById(R.id.async_view);
        tv.setText(aString);

    }

    private class AsyncTasker extends AsyncTask<String, Integer, String>{

        @Override
        protected String doInBackground(String... arg0) {

            AssetManager am = GoodAsync.this.getAssets();
            String string = "";
            try {
                // Code that reads a file and stores it in the string variable

                return string;

            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
            return null;
        }

        @Override
        protected void onPostExecute(String result) {
            super.onPostExecute(result);
            aString = result;
        }   

    }
}

Answer 1

Perhaps you want to do it like this:

public class GoodAsync extends Activity{

TextView tv;

@Override
protected void onCreate(Bundle savedInstanceState) {
    // TODO Auto-generated method stub
    super.onCreate(savedInstanceState);
    setContentView(R.layout.asynctasks);
    tv = (TextView) findViewById(R.id.async_view);
    new AsyncTasker().execute();
}

    public void setTextView (String text) {
       tv.setText(text);
    }

    private class AsyncTasker extends AsyncTask<String, Integer, String>{

        ....

        @Override
        protected void onPostExecute(String result) {
            super.onPostExecute(result);
            setTextView(result);
        }   

    }
}

Answer 2

Are you sure your AsyncTask is executing in time?

eg You are doing this:

new AsyncTasker().execute();
tv = (TextView) findViewById(R.id.async_view);
tv.setText(aString);

This sets the task going but then immediately sets the value of the TextView to the aString variable.

The AsyncTask is most likely still executing at this point so aString only gets a value other than "nothing" after the code has executed.

Answer 3

You are not waiting for your asynctask to finish..you can do it like this..

new AsyncTasker().execute().get();
tv = (TextView) findViewById(R.id.async_view);
tv.setText(aString);