从 Activity 中的异步任务获取价值

Question

我有一个 class，如下所示。它位于名为 NQRequestHandler.java 的 .java 文件中，我想从 Activity.java 中调用它。但是我在使用 AsyncTask 方法时遇到了问题。当我运行它在 Activity.java 文件中它 returns 一个空当我尝试从 Activity 中记录 Globals.PUBLIC_KEY 的值时的值。 Log.v("RESULT", "Public KEY JSON from OnStart" + Globals.PUBLIC_KEY);

public class NQRequestHandler {

    private static NQRequestHandler instance;
    public static final String TAG = NQRequestHandler.class.getSimpleName();
    private Context mContext;


public NQRequestHandler(Context context) {
    mContext = context;
}

public static synchronized NQRequestHandler getInstance(Context context) {

    if (instance == null)
        instance = new NQRequestHandler(context);

    return instance;
}

public class requestHandler extends AsyncTask<String, Void, JSONArray> {

    RequestListener requestListener;
    public JSONArray requestResult;

    public requestHandler() {

    }

    public void setRequestListener(RequestListener requestListener) {
        this.requestListener = requestListener;
    }

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

        try {
            String url = "http://www.someurl.com";

            HttpClient client = new DefaultHttpClient();
            HttpPost post = new HttpPost(url);

            List<NameValuePair> urlParameters = requestHandlerHelper(params);
            UrlEncodedFormEntity entity = new UrlEncodedFormEntity(urlParameters);

            entity.setContentType(new BasicHeader(HTTP.CONTENT_TYPE, "application/x-www-form-urlencoded; charset=UTF-8"));
            post.setEntity(entity);

            HttpResponse response = client.execute(post);
            System.out.println("Response Code : " + response.getStatusLine().getStatusCode());

            Reader reader = new InputStreamReader(response.getEntity().getContent());

            int contentLength = (int) response.getEntity().getContentLength();
            Log.v(TAG, "Content Length DATA" + contentLength);
            char[] charArray = new char[contentLength];
            reader.read(charArray);

            String responseData = new String(charArray);
            JSONArray jsonResponse = new JSONArray(responseData);

            return jsonResponse;

        } catch (ClientProtocolException e) {
            Log.i(TAG, "ClientProtocolException: ", e);
        } catch (UnsupportedEncodingException e) {
            Log.i(TAG, "UnsupportedEncodingException: ", e);
        } catch (IOException e) {
            Log.i(TAG, "IOException: ", e);
        } catch (JSONException e) {
            Log.i(TAG, "JSONException: ", e);
        }
        return null;
    }

    @Override
    protected void onPostExecute(JSONArray results) {
        if (results != null) {
            requestListener.onRequestSuccess(results);
        } else {
            requestListener.onRequestFailed();
        }
    }

}

public interface RequestListener {
    JSONArray onRequestSuccess(JSONArray data);

    void onRequestFailed();
}

public void NQRequest(String... params) {
    if (isNetworkAvailable()) {
        requestHandler handler = new requestHandler();
        RequestListener listener = new RequestListener() {
            @SuppressWarnings("unchecked")
            @Override
            public JSONArray onRequestSuccess(JSONArray data) {
                //TODO: Switch set data here

                Log.v(TAG, "JSON FROM NQRequest" + data);
                Globals.PUBLIC_KEY = String.valueOf(data);
                return data;
            }

            @Override
            public void onRequestFailed() {
                Toast.makeText(mContext, "Network is unavailable. Request failed", Toast.LENGTH_LONG).show();
            }
        };
        handler.setRequestListener(listener);
        handler.execute(params);
    } else {
        Toast.makeText(mContext, "Network is unavailable", Toast.LENGTH_LONG).show();
    }
}

private static List<NameValuePair> requestHandlerHelper(String... params) {

    //Declare URL Parameter values
    List<NameValuePair> urlParameters = new ArrayList<NameValuePair>();
    String[] requestActionArray = Globals.REQUEST_ACTION_ID;
    int actionSwitch = -1;
    String[] requestActionHeaders = null;

    //Find URL Parameter Action Switch
    for (int i = 0; i < requestActionArray.length; i++) {
        if (requestActionArray[i].equalsIgnoreCase(params[params.length - 1])) {
            actionSwitch = i;
        }
    }

    //Set Action Switch ID Parameters
    requestActionHeaders = NQActionHeader(actionSwitch);

    //Set URL Parameters
    for (int i = 0; i < requestActionHeaders.length; i++) {
        urlParameters.add(new BasicNameValuePair(requestActionHeaders[i], params[i]));
    }

    return urlParameters;
}

private boolean isNetworkAvailable() {
    ConnectivityManager manager =
            (ConnectivityManager) mContext.getSystemService(Context.CONNECTIVITY_SERVICE);
    NetworkInfo networkInfo = manager.getActiveNetworkInfo();

    return networkInfo != null && networkInfo.isConnected() ? true : false;
}

private static String[] NQActionHeader(int actionSwitch) {
    /* some code goes here */
    }
}

在 Activity class 中看起来是这样的：

public class Application extends Activity {

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    try {
        String message = "Hello World from Android";
            Context mContext = getBaseContext();
            NQRequestHandler.requestHandler handler = new     NQRequestHandler.requestHandler();
            NQRequestHandler requestHandler = NQRequestHandler.getInstance(mContext);
            requestHandler.NQRequest(message, "sendPublicKey");

        Log.v("RESULT", "Public KEY JSON from OnStart" + Globals.PUBLIC_KEY);
        //Start Activity
        Intent intent = new Intent(this, LoginActivity.class);
        intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
        intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TASK);
        startActivity(intent);
    } catch (Exception e) {
        e.printStackTrace();
    }
  }
}

在Activity中对NQRequest的调用启动了在Activity中对AsyncTask的调用。有什么帮助吗？如何在 Activity.java 中实现回调以从 NQRequest() 中的 OnRequestSuccess(); 获取方法？注意：我正在尝试在其他多个 Activity.java 文件

中调用 Activity.java 中的方法

Answer 1

来自 OnStart 的日志应该 return Globals.PUBLIC_KEY 的空值。您刚刚将一个异步任务设置为运行设置该值。到日志语句执行时，它还没有运行。您应该收到来自

的日志输入

Log.v(TAG, "JSON FROM NQRequest" + data);

打电话。这主要发生在您的 activity 完成 onCreate 之后，因为它是一个异步调用。

Answer 2

我修改了结构供大家参考。

requestHandler 的修改：-

//**** e.g.
class requestHandler extends AsyncTask<Object, Void, JSONArray> {
    // define a caller

    String requester;
    Application caller;
    YourEachActivityClass1 caller1;

    //create a Constructor for caller;
    public requestHandler (Application caller) {
        // TODO Auto-generated constructor stub
         this.caller = caller;
    }

    public requestHandler (YourEachActivityClass1 caller1) {
        // TODO Auto-generated constructor stub
         this.caller1 = caller1;
    }

    ///&& method doInBackground
    @Override
    protected JSONArray doInBackground(Object... params) {
          .....
          //your process is here
         //custom your returning jsonarray

    try {

    Context context = (Context) params[0];
    Log.i(TAG, "context :"+context.getClass().getSimpleName());

    requester = (Integer) params[1];

    String message = (String) params[2];

    String public= (String) params[3]

        String url = "http://www.someurl.com";

        HttpClient client = new DefaultHttpClient();
        HttpPost post = new HttpPost(url);

        List<NameValuePair> urlParameters = requestHandlerHelper(params);
        UrlEncodedFormEntity entity = new UrlEncodedFormEntity(urlParameters);

        entity.setContentType(new BasicHeader(HTTP.CONTENT_TYPE, "application/x-www-form-urlencoded; charset=UTF-8"));
        post.setEntity(entity);

        HttpResponse response = client.execute(post);
        System.out.println("Response Code : " + response.getStatusLine().getStatusCode());

        Reader reader = new InputStreamReader(response.getEntity().getContent());

        int contentLength = (int) response.getEntity().getContentLength();
        Log.v(TAG, "Content Length DATA" + contentLength);
        char[] charArray = new char[contentLength];
        reader.read(charArray);

        String responseData = new String(charArray);
        JSONArray jsonResponse = new JSONArray(responseData);

        Globals.PUBLIC_KEY = String.valueOf(jsonResponse);

        return jsonResponse;

    } catch (ClientProtocolException e) {
        Log.i(TAG, "ClientProtocolException: ", e);
    } catch (UnsupportedEncodingException e) {
        Log.i(TAG, "UnsupportedEncodingException: ", e);
    } catch (IOException e) {
        Log.i(TAG, "IOException: ", e);
    } catch (JSONException e) {
        Log.i(TAG, "JSONException: ", e);
    }
    return null;

    }

    ////&& return JSONArray back to ur activity class here by pass in caller
    protected void onPostExecute(JSONArray jsonarray) {

        if(requester.equals("IM_Application"))
            caller.onBackgroundTaskCompleted(jsonarray);
        else if(requester.equals("IM_ACTIVITY_1"))
            caller1.onBackgroundTaskCompleted(jsonarray);
    }

}

Application.class 获取你的 json 对象：-

public class Application extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        try {
            String message = "Hello World from Android";
             new requestHandler(this).execute(getActivity(), "IM_Application", message, "sendPublicKey");

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

        //your returning result
public void onBackgroundTaskCompleted(JSONArray jsonarray) {
        Log.i("TAG", jsonarray:"+jsonarray);

        if(jsonarray!=null){
            //process your jsonarray to get the Globals.PUBLIC_KEY)here

                    Log.v("onBackgroundTaskCompleted", "Public KEY JSON from OnStart" + Globals.PUBLIC_KEY);
                    //Start Activity
                    Intent intent = new Intent(this, LoginActivity.class);
                    intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
                    intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TASK);
                    startActivity(intent);


         }else{
         Toast.makeText(mContext, "Network is unavailable. Request failed", Toast.LENGTH_LONG).show();
         }

}

}

祝你好运:)

Answer 3

已修复，现在可以使用了。

public class HQHandler extends AsyncTask<String, Void, JSONArray> {

    public static final String TAG = HQHandler.class.getSimpleName();
    private static HQHandler instance;
    RequestListener requestListener;
    JSONArray requestResult;
    Context mContext;

    public HQHandler(Context context) {
        this.mContext = context;
    }

    public static synchronized HQHandler getInstance(Context context) {

        if (instance == null)
            instance = new HQHandler(context);

        return instance;
    }

    public void setRequestListener(RequestListener requestListener) {
        this.requestListener = requestListener;
    }

    public JSONArray getRequestResult() {
        return this.requestResult;
    }

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

        try {
            String url = "http://www.someurl.com";

            HttpClient client = new DefaultHttpClient();
            HttpPost post = new HttpPost(url);

            List<NameValuePair> urlParameters = requestHandlerHelper(params);
            UrlEncodedFormEntity entity = new UrlEncodedFormEntity(urlParameters);

            entity.setContentType(new BasicHeader(HTTP.CONTENT_TYPE, "application/x-www-form-urlencoded; charset=UTF-8"));
            post.setEntity(entity);

            HttpResponse response = client.execute(post);
            System.out.println("Response Code : " + response.getStatusLine().getStatusCode());

            Reader reader = new InputStreamReader(response.getEntity().getContent());

            int contentLength = (int) response.getEntity().getContentLength();
            Log.v(TAG, "Content Length DATA" + contentLength);
            char[] charArray = new char[contentLength];
            reader.read(charArray);

            String responseData = new String(charArray);
            JSONArray jsonResponse = new JSONArray(responseData);

            return jsonResponse;

        } catch (ClientProtocolException e) {
            Log.i(TAG, "ClientProtocolException: ", e);
        } catch (UnsupportedEncodingException e) {
            Log.i(TAG, "UnsupportedEncodingException: ", e);
        } catch (IOException e) {
            Log.i(TAG, "IOException: ", e);
        } catch (JSONException e) {
            Log.i(TAG, "JSONException: ", e);
        }
        return null;
    }

    @Override
    protected void onPostExecute(JSONArray results) {
        if (results != null) {
            requestListener.onRequestSuccess(results);
        } else {
            requestListener.onRequestFailed();
        }
    }

    public interface RequestListener {
        JSONArray onRequestSuccess(JSONArray data);

        void onRequestFailed();
    }

    public JSONArray HQRequest(String... params) throws ExecutionException, InterruptedException, JSONException {
        JSONArray result;

        if (!isNetworkAvailable()) {
            Toast.makeText(mContext, "Network is unavailable", Toast.LENGTH_LONG).show();
            return null;
        }

        HQHandler handler = new HQHandler(this.mContext);
        RequestListener listen = new RequestListener() {
            @SuppressWarnings("unchecked")
            @Override
            public JSONArray onRequestSuccess(JSONArray data) {
                return data;
            }

            @Override
            public void onRequestFailed() {
                Toast.makeText(mContext, "Network is unavailable. Request failed", Toast.LENGTH_LONG).show();
            }
        };
        handler.setRequestListener(listen);
        result = this.requestResult = handler.execute(params).get();

        return result;

    }

}

从 Activity 中的异步任务获取价值

Get value from Async task in Activity

java

android

android-asynctask