完美的解决如何让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

001	packagecom.isummation.exampleapp;

002

003	importjava.io.BufferedReader;

004	importjava.io.InputStreamReader;

005	importjava.net.URLEncoder;

006	importjava.net.UnknownHostException;

007

008	importorg.apache.http.HttpResponse;

009	importorg.apache.http.client.HttpClient;

010	importorg.apache.http.client.methods.HttpGet;

011	importorg.apache.http.impl.client.DefaultHttpClient;

012	importorg.apache.http.params.CoreProtocolPNames;

013	importorg.apache.http.protocol.BasicHttpContext;

014	importorg.apache.http.protocol.HttpContext;

015	importorg.json.JSONObject;

016

017	importandroid.app.Activity;

018	importandroid.app.Dialog;

019	importandroid.app.ProgressDialog;

020	importandroid.content.DialogInterface;

021	importandroid.content.DialogInterface.OnCancelListener;

022	importandroid.os.AsyncTask;

023	importandroid.os.Bundle;

024	importandroid.view.View;

025	importandroid.view.View.OnClickListener;

026	importandroid.widget.Button;

027	importandroid.widget.EditText;

028	importandroid.widget.Toast;

029

030	publicclassUserLoginextendsActivity {

031

032	privateEditText etUsername;

033	privateEditText etPassword;

034	privateProgressDialog progressDialog;

035	privatestaticfinalintPROGRESSDIALOG_ID =0;

036	privatestaticfinalintSERVER_ERROR =1;

037	privatestaticfinalintNETWORK_ERROR =2;

038	privatestaticfinalintCANCELLED =3;

039	privatestaticfinalintSUCCESS =4;

040	privateString ServerResponse;

041	privateLoginTask loginTask;

042

043

@Override

044	publicvoidonCreate(Bundle savedInstanceState) {

045	super.onCreate(savedInstanceState);

046	setContentView(R.layout.login);

047

048	etUsername = (EditText) findViewById(R.id.txt_username);

049	etPassword = (EditText) findViewById(R.id.txt_password);

050

051	Button login_button = (Button)this.findViewById(R.id.login_button);

052	login_button.setOnClickListener(newOnClickListener() {

053	publicvoidonClick(View viewParam) {

054	if(etUsername.getText().toString().length() ==0

055	|| etPassword.getText().toString().length() ==0) {

056	Toast.makeText(getApplicationContext(),

057	"Please enter username and password",

058	Toast.LENGTH_SHORT).show();

059

}else{

060

061	//Show dialog by passing id

062	showDialog(PROGRESSDIALOG_ID);

063

}

064

}

065

});

066

}

067

068	protectedDialog onCreateDialog(intid) {

069	switch(id) {

070	casePROGRESSDIALOG_ID:

071	removeDialog(PROGRESSDIALOG_ID);

072

073	//Please note that forth parameter is true for cancelable Dialog

074	//Also register cancel event listener

075	//if the litener is registered then forth parameter has no effect

076	progressDialog = ProgressDialog.show(UserLogin.this,"Authenticating",

077	"Please wait...",true,true,newOnCancelListener(){

078

079	publicvoidonCancel(DialogInterface dialog) {

080	//Check the status, status can be RUNNING, FINISHED and PENDING

081	//It can be only cancelled if it is not in FINISHED state

082	if(loginTask !=null&& loginTask.getStatus() != AsyncTask.Status.FINISHED)

083	loginTask.cancel(true);

084

}

085

});

086

break;

087

default:

088	progressDialog =null;

089

}

090	returnprogressDialog;

091

}

092

093

@Override

094	protectedvoidonPrepareDialog(intid, Dialog dialog) {

095	switch(id) {

096	casePROGRESSDIALOG_ID:

097	//check if any previous task is running, if so then cancel it

098	//it can be cancelled if it is not in FINISHED state

099	if(loginTask !=null&& loginTask.getStatus() != AsyncTask.Status.FINISHED)

100	loginTask.cancel(true);

101	loginTask =newLoginTask();//every time create new object, as AsynTask will only be executed one time.

102	loginTask.execute();

103

}

104

}

105

106	classLoginTaskextendsAsyncTask<Void, Integer, Void> {

107

@Override

108	protectedVoid doInBackground(Void... unused) {

109

try{

110	ServerResponse =null;//don't forget to make it null, as task can be called again

111	HttpClient httpClient =newDefaultHttpClient();

112	HttpContext localContext =newBasicHttpContext();

113	HttpGet httpGet =newHttpGet(

114	getString(R.string.WebServiceURL)

115	+"/cfc/iphonewebservice.cfc?returnformat=json&method=validateUserLogin&username="

116	+ URLEncoder.encode(etUsername.getText()

117	.toString(),"UTF-8")

118	+"&password="

119	+ URLEncoder.encode(etPassword.getText()

120	.toString(),"UTF-8"));

121	httpClient.getParams().setParameter(

122	CoreProtocolPNames.USER_AGENT,"Some user agent string");

123

124	//call it just before you make server call

125	//calling after this statement and canceling task will no meaning if you do some update database kind of operation

126	//so be wise to choose correct place to put this condition

127	//you can also put this condition in for loop, if you are doing iterative task

128

129	//now this very important

130	//if you do not put this condition and not maintaining execution, then there is no meaning of calling .cancel() method

131	//you should only check this condition in doInBackground() method, otherwise there is no logical meaning

132	if(isCancelled())

133

{

134	publishProgress(CANCELLED);//Notify your activity that you had canceled the task

135	return(null);// don't forget to terminate this method

136

}

137	HttpResponse response = httpClient.execute(httpGet,

138	localContext);

139

140	BufferedReader reader =newBufferedReader(

141	newInputStreamReader(

142	response.getEntity().getContent(),"UTF-8"));

143	ServerResponse = reader.readLine();

144	publishProgress(SUCCESS);//if everything is Okay then publish this message, you may also use onPostExecute() method

145	}catch(UnknownHostException e) {

146	removeDialog(PROGRESSDIALOG_ID);

147	e.printStackTrace();

148	publishProgress(NETWORK_ERROR);

149	}catch(Exception e) {

150	removeDialog(PROGRESSDIALOG_ID);

151	e.printStackTrace();

152	publishProgress(SERVER_ERROR);

153

}

154	return(null);

155

}

156

157

@Override

158	protectedvoidonProgressUpdate(Integer... errorCode) {

159	switch(errorCode[0]) {

160	caseCANCELLED:

161	removeDialog(PROGRESSDIALOG_ID);

162	Toast.makeText(getApplicationContext(),"Cancelled by user",

163	Toast.LENGTH_LONG).show();

164

break;

165	caseNETWORK_ERROR:

166	removeDialog(PROGRESSDIALOG_ID);

167	Toast.makeText(getApplicationContext(),"Network connection error",

168	Toast.LENGTH_LONG).show();

169

break;

170	caseSERVER_ERROR:

171	removeDialog(PROGRESSDIALOG_ID);

172	Toast.makeText(getApplicationContext(),"Server error",

173	Toast.LENGTH_LONG).show();

174

break;

175	caseSUCCESS:

176	removeDialog(PROGRESSDIALOG_ID);

177

try{

178	if(ServerResponse !=null) {

179	JSONObject JResponse =newJSONObject(ServerResponse);

180	String sMessage = JResponse.getString("MESSAGE");

181	intsuccess = JResponse.getInt("SUCCESS");

182	if(success ==1) {

183	//proceed further

184

185	//you may start new activity from here

186	//after that you may want to finish this activity

187	UserLogin.this.finish();

188

189	//Remember when you finish an activity, it doesn't mean that you also finish thread or AsynTask started within that activity

190	//So you must implement onDestroy() method and terminate those threads.

191

}else{

192	//just showing invalid username password from server response

193	Toast.makeText(getApplicationContext(), sMessage,

194	Toast.LENGTH_SHORT).show();

195

}

196

}

197	}catch(Exception e){

198	Toast.makeText(getApplicationContext(),"Server error",

199	Toast.LENGTH_LONG).show();

200	e.printStackTrace();

201

}

202

break;

203

}

204

}

205

206

@Override

207	protectedvoidonPostExecute(Void unused) {

208

209

}

210

}

211

212

@Override

213	protectedvoidonDestroy(){

214	//you may call the cancel() method but if it is not handled in doInBackground() method

215	if(loginTask !=null&& loginTask.getStatus() != AsyncTask.Status.FINISHED)

216	loginTask.cancel(true);

217	super.onDestroy();

218

}

219

}

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

标签： Android SDK AsyncTask

补充话题说明»

按默认排序|显示最新评论|回页面顶部共有1个评论发表评论»

• 
  PengTesun回答于 2012-02-13 11:38 (2个月前)

  举报

  这个取消其实不是完美的，当执行到 HttpResponse response = httpClient.execute(httpGet, localContext);时，是不能取消的，而恰恰是这后面的等待过程需求取消操作