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。
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();
}
}
