Question

我有一个Android应用程序，它包含一个活动和一个扩展AsyncTask的java类。所以我在java类中有一个名为 resFromServer 的String 我希望在一个合适的Android小部件中显示它，如Alertdialog。

我希望有人帮助我如何从活动中访问该字符串

public class JSONTransmitter extends AsyncTask<JSONObject, JSONObject, JSONObject> {

    String url = "http://192.168.1.8:89/Derdeery/b.php";



    protected JSONObject doInBackground(JSONObject... data) {
        JSONObject json = data[0];

        HttpClient client = new DefaultHttpClient();
        HttpConnectionParams.setConnectionTimeout(client.getParams(), 100000);
        StrictMode.setThreadPolicy(new StrictMode.ThreadPolicy.Builder().permitNetwork().build());
        JSONObject jsonResponse = null;

        HttpPost post = new HttpPost(url);

        try {
            StringEntity se = new StringEntity("json="+json.toString());

            post.addHeader("content-type", "application/x-www-form-urlencoded");
            post.setEntity(se);

            HttpResponse response;
            response = client.execute(post);
            String resFromServer = org.apache.http.util.EntityUtils.toString(response.getEntity());


               Log.i("Response from server", **resFromServer**);


        } 
        catch (Exception e)
        { e.printStackTrace();}

        return jsonResponse;
    }

}

活动

public class MainActivity extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) 
       {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        } }

Answer 1

正确的解决方案：创建instance的{{1}}并进行回调，以便将响应捕获到任何AsyncTask中。将实现此接口的所有活动都可以检索AsyncTask的结果。这更灵活，只需一个AsyncTask即可由多个活动使用。

您必须在Activity中创建实例并返回String响应：

AsyncTask

然后，您可以通过将public class JSONTransmitter extends AsyncTask<JSONObject, Void, String> { private AsyncCallback asyncCallback; // callback variable // constructor public JSONTransmitter(Context context) { // attach the callback to any context asyncCallback = (AsyncCallback) context; } // create the interface public static interface AsyncCallback { void onResponse(String res); } ... @Override protected void onPostExecute(String result) { super.onPostExecute(result); if (asyncCallback != null) { // call the onResponse method for callback asyncCallback.onResponse(result); } } }设置为Activity来实现任何Context回调：

public class MainActivity extends Activity implements JSONTransmitter.AsyncCallback {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        // set the Context to the AsyncTask when you create it
        // in order to return here and execute the request
        new JSONTransmitter(this).execute(...);
    } 

    ...
    @Override
    public void onResponse(String res) {
        // handle the string response when it's called from onPostExecute()
        Log.v("From_MainActivity", "AsyncTask returns this: "+res);
    }
}

因此，您可以使用Activity类resFromServer AsyncTask（结果字符串）在self中执行您想要的操作。

Answer 2

将您的活动作为参数传递给AsyncTask类构造函数：

class MyAsyncTask extends AsyncTask<URL, Integer, Long> {

    Activity mActivity;

    public MyAsyncTask(Activity activity) {
       mActivity = ativity;
    }

然后更新您的活动：

 @Override
    protected void onPostExecute(String result) {
         super.onPostExecute(result);
         int id = mActivity.findViewById(...);
  }

您不应使用doInBackground方法更新活动。使用onPostExecute，因为它使用主线程。

在活动窗口小部件中显示Java类的字符串

2 个答案: