我有一个课程，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。但是我遇到了AsyncTask方法的问题。当我在Activity.java文件中运行它时，它返回null
我尝试从Activity中记录Globals.PUBLIC_KEY的值时的值。
Log.v（“结果”，“来自OnStart的公钥JSON”+ 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类中如下所示：
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中调用NQRequest会在Activity中启动对AsyncTask的调用。对此有何帮助？如何在Activity.java中实现回调以从OnRequestSuccess();中的NQRequest()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
答案 0 :(得分：1)
OnStart中的日志应返回Globals.PUBLIC_KEY的空值。您刚刚设置了一个异步任务来运行以设置该值。到日志语句执行时它还没有运行。您应该从
收到日志输入Log.v(TAG, "JSON FROM NQRequest" + data);
呼叫。这将主要发生在您的活动完成onCreate之后，因为它是异步调用。
答案 1 :(得分：1)
我修改了结构供您参考。
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();
}
}
}
Gd Luck：）
答案 2 :(得分：0)
修正了它现在有效。
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;
}
}