解决如何让AsyncTask终止操作

受到这个的启发终于结局了如何在AsyncTask运行中终止其操作。

单纯的onCancelled(true)是不行的

下面把代码贴出来~实现了登陆功能。

AsyncTask简介，它使创建需要与用户界面交互的长时间运行的任务变得更简单。相对来说AsyncTask更轻量级一些，适用于简单的异步处理，不需要借助线程和Handler即可实现。

转自stackoverflow

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package com.isummation.exampleapp;    import java.io.BufferedReader; import java.io.InputStreamReader; import java.net.URLEncoder; import java.net.UnknownHostException;    import org.apache.http.HttpResponse; import org.apache.http.client.HttpClient; import org.apache.http.client.methods.HttpGet; import org.apache.http.impl.client.DefaultHttpClient; import org.apache.http.params.CoreProtocolPNames; import org.apache.http.protocol.BasicHttpContext; import org.apache.http.protocol.HttpContext; import org.json.JSONObject;    import android.app.Activity; import android.app.Dialog; import android.app.ProgressDialog; import android.content.DialogInterface; import android.content.DialogInterface.OnCancelListener; import android.os.AsyncTask; import android.os.Bundle; import android.view.View; import android.view.View.OnClickListener; import android.widget.Button; import android.widget.EditText; import android.widget.Toast;    public class UserLogin extends Activity {        private EditText etUsername;     private EditText etPassword;     private ProgressDialog progressDialog;     private static final int PROGRESSDIALOG_ID = 0;     private static final int SERVER_ERROR = 1;     private static final int NETWORK_ERROR = 2;     private static final int CANCELLED = 3;     private static final int SUCCESS = 4;     private String ServerResponse;     private LoginTask loginTask;        @Override     public void onCreate(Bundle savedInstanceState) {         super.onCreate(savedInstanceState);         setContentView(R.layout.login);            etUsername = (EditText) findViewById(R.id.txt_username);         etPassword = (EditText) findViewById(R.id.txt_password);            Button login_button = (Button) this.findViewById(R.id.login_button);         login_button.setOnClickListener(new OnClickListener() {             public void onClick(View viewParam) {                 if (etUsername.getText().toString().length() == 0                         || etPassword.getText().toString().length() == 0) {                     Toast.makeText(getApplicationContext(),                             "Please enter username and password",                             Toast.LENGTH_SHORT).show();                 } else {                        //Show dialog by passing id                     showDialog(PROGRESSDIALOG_ID);                 }             }         });     }        protected Dialog onCreateDialog(int id) {         switch(id) {         case PROGRESSDIALOG_ID:             removeDialog(PROGRESSDIALOG_ID);                //Please note that forth parameter is true for cancelable Dialog             //Also register cancel event listener             //if the litener is registered then forth parameter has no effect             progressDialog = ProgressDialog.show(UserLogin.this, "Authenticating",                     "Please wait...", true, true, new OnCancelListener(){                            public void onCancel(DialogInterface dialog) {                             //Check the status, status can be RUNNING, FINISHED and PENDING                             //It can be only cancelled if it is not in FINISHED state                             if (loginTask != null && loginTask.getStatus() != AsyncTask.Status.FINISHED)                                 loginTask.cancel(true);                         }                     });             break;         default:             progressDialog = null;         }         return progressDialog;     }        @Override     protected void onPrepareDialog(int id, Dialog dialog) {         switch (id) {         case PROGRESSDIALOG_ID:             //check if any previous task is running, if so then cancel it             //it can be cancelled if it is not in FINISHED state             if (loginTask != null && loginTask.getStatus() != AsyncTask.Status.FINISHED)                 loginTask.cancel(true);             loginTask = new LoginTask(); //every time create new object, as AsynTask will only be executed one time.             loginTask.execute();         }     }        class LoginTask extends AsyncTask<Void, Integer, Void> {         @Override         protected Void doInBackground(Void... unused) {             try {                 ServerResponse = null; //don't forget to make it null, as task can be called again                 HttpClient httpClient = new DefaultHttpClient();                 HttpContext localContext = new BasicHttpContext();                 HttpGet httpGet = new HttpGet(                         getString(R.string.WebServiceURL)                                 + "/cfc/iphonewebservice.cfc?returnformat=json&method=validateUserLogin&username="                                 + URLEncoder.encode(etUsername.getText()                                         .toString(), "UTF-8")                                 + "&password="                                 + URLEncoder.encode(etPassword.getText()                                         .toString(), "UTF-8"));                 httpClient.getParams().setParameter(                         CoreProtocolPNames.USER_AGENT,"Some user agent string");                    //call it just before you make server call                 //calling after this statement and canceling task will no meaning if you do some update database kind of operation                 //so be wise to choose correct place to put this condition                 //you can also put this condition in for loop, if you are doing iterative task                    //now this very important                 //if you do not put this condition and not maintaining execution, then there is no meaning of calling .cancel() method                 //you should only check this condition in doInBackground() method, otherwise there is no logical meaning                 if (isCancelled())                 {                     publishProgress(CANCELLED); //Notify your activity that you had canceled the task                     return (null); // don't forget to terminate this method                 }                 HttpResponse response = httpClient.execute(httpGet,                         localContext);                    BufferedReader reader = new BufferedReader(                         new InputStreamReader(                                 response.getEntity().getContent(), "UTF-8"));                 ServerResponse = reader.readLine();                 publishProgress(SUCCESS); //if everything is Okay then publish this message, you may also use onPostExecute() method             } catch (UnknownHostException e) {                 removeDialog(PROGRESSDIALOG_ID);                 e.printStackTrace();                 publishProgress(NETWORK_ERROR);             } catch (Exception e) {                 removeDialog(PROGRESSDIALOG_ID);                 e.printStackTrace();                 publishProgress(SERVER_ERROR);             }             return (null);         }            @Override         protected void onProgressUpdate(Integer... errorCode) {             switch (errorCode[0]) {             case CANCELLED:                 removeDialog(PROGRESSDIALOG_ID);                 Toast.makeText(getApplicationContext(), "Cancelled by user",                         Toast.LENGTH_LONG).show();                 break;             case NETWORK_ERROR:                 removeDialog(PROGRESSDIALOG_ID);                 Toast.makeText(getApplicationContext(), "Network connection error",                         Toast.LENGTH_LONG).show();                 break;             case SERVER_ERROR:                 removeDialog(PROGRESSDIALOG_ID);                 Toast.makeText(getApplicationContext(), "Server error",                         Toast.LENGTH_LONG).show();                 break;             case SUCCESS:                 removeDialog(PROGRESSDIALOG_ID);                 try {                     if (ServerResponse != null) {                         JSONObject JResponse = new JSONObject(ServerResponse);                         String sMessage = JResponse.getString("MESSAGE");                         int success = JResponse.getInt("SUCCESS");                         if (success == 1) {                             //proceed further                                //you may start new activity from here                             //after that you may want to finish this activity                             UserLogin.this.finish();                                //Remember when you finish an activity, it doesn't mean that you also finish thread or AsynTask started within that activity                             //So you must implement onDestroy() method and terminate those threads.                         } else {                             //just showing invalid username password from server response                             Toast.makeText(getApplicationContext(), sMessage,                                     Toast.LENGTH_SHORT).show();                         }                     }                 } catch (Exception e){                     Toast.makeText(getApplicationContext(), "Server error",                             Toast.LENGTH_LONG).show();                     e.printStackTrace();                 }                 break;             }         }            @Override         protected void onPostExecute(Void unused) {            }     }        @Override     protected void onDestroy(){         //you may call the cancel() method but if it is not handled in doInBackground() method         if (loginTask != null && loginTask.getStatus() != AsyncTask.Status.FINISHED)             loginTask.cancel(true);         super.onDestroy();     } }

原文出处：http://www.ericyue.info/archive/stop-asynctask#more-1117