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我遇到了AsyncTaskdoInBackground方法的问题，我不知道如何阻止此方法运行。在Android中停止AsyncTask doInBackground方法
我正在处理一个应用程序，该应用程序具有一个登录屏幕，用于检索有关登录用户的信息。问题是，当我输入了错误的密码或用户名，然后当我重新输入正确的数据，我的应用程序崩溃，我得到
“java.lang.IllegalStateException：无法执行任务：任务有 已经已执行“
如何阻止此线程运行？下面是代码：
LoginActivity.java
public class LoginActivity extends Activity implements LoginParser.GetLoginListener{
public LoginParser parser1;
public EditText ETUsername;
public EditText ETPassword;
//private LoginParser lb;
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_login);
parser1 = new LoginParser();
ETUsername = (EditText)findViewById(R.id.ET1);
ETPassword = (EditText)findViewById(R.id.ET2);
final Button button = (Button) findViewById(R.id.loginBut);
button.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
String UserName = ETUsername.getText().toString();
String Password = ETPassword.getText().toString();
Log.e("LoginAct .. userName: ", UserName);
Log.e("LoginAct .. Password: ", Password);
if (UserName.isEmpty() || Password.isEmpty()) {
new AlertDialog.Builder(LoginActivity.this).setTitle("Warning")
.setMessage("Please Enter your Username and Password")
.setPositiveButton("OK", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
}
}).show();
}
else{
parser1.getLoginInfo(UserName, Password);
parser1.setListener(LoginActivity.this);
}
} // end of button on click
});
}
@Override
public void didReceivedUserInfo(String displayName) {
if(displayName != null) {
new AlertDialog.Builder(LoginActivity.this).setTitle("Welcome").setMessage("Welcome " + displayName)
.setPositiveButton("OK", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
Intent in = new Intent (LoginActivity.this, MainActivity.class);
startActivity(in);
}
}).show();
}
else {
new AlertDialog.Builder(LoginActivity.this).setTitle("Warning")
.setMessage("Error in login ID or Password, Please try again later")
.setPositiveButton("OK", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
}
}).show();
}
}
}
LoginParser.java
public class LoginParser extends AsyncTask <Void,Void,String> {
private String requestURL;
public String UserName ;
public String Password ;
public interface GetLoginListener
{
public void didReceivedUserInfo (String displayName);
}
private GetLoginListener listener;
public GetLoginListener getListener() {
return listener;
}
public void setListener(GetLoginListener listener) {
this.listener = listener;
}
public void getLoginInfo(String userName , String password)
{
requestURL = "some link";
this.UserName = userName ;
this.Password = password ;
execute(); // it will call doInBackground in secondary thread
}
@Override
protected String doInBackground(Void... params) {
try {
URL url = new URL(requestURL);
HttpURLConnection urlConnection1 = (HttpURLConnection) url.openConnection();
String jsonString = "LID="+ UserName +"&PWD="+Password+"&Passcode=****";
Log.e("LoginParser","JSONString: " + jsonString);
urlConnection1.setDoOutput(true);
urlConnection1.setRequestMethod("POST");
urlConnection1.setRequestProperty("Content-Type", "application/x-www-form-urlencoded");
urlConnection1.setRequestProperty("charset","utf-8");
PrintWriter out = new PrintWriter(urlConnection1.getOutputStream());
// out.print(this.requestMessage);
out.print(jsonString);
out.close();
int statusCode = urlConnection1.getResponseCode();
Log.d("statusCode", String.valueOf(statusCode));
StringBuilder response = new StringBuilder();
byte[] data = null;
if (statusCode == HttpURLConnection.HTTP_OK)
{
BufferedReader r = new BufferedReader(new InputStreamReader(urlConnection1.getInputStream()));
String line;
while ((line = r.readLine()) != null) {
response.append(line);
}
data = response.toString().getBytes();
}
else {
data = null;// failed to fetch data
}
String responseString = new String(data);
Log.e("doInBackground", "responseString" + responseString);
JSONObject jsonObject2 = new JSONObject(responseString);
String Status = jsonObject2.getString("Status");
Log.e("Status", Status);
if (Status.equals("s")) {
Log.i("Status:", "Successful");
String displayName = jsonObject2.getString("DisplayName");
return displayName;
}
else {
return null;
}
} catch (ProtocolException e) {
e.printStackTrace();
} catch (MalformedURLException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} catch (JSONException e) {
e.printStackTrace();
}
return null;
}
@Override
protected void onPostExecute(String displayName) {
super.onPostExecute(displayName);
Log.e("onPost: ","onPost");
listener.didReceivedUserInfo(displayName);
}
}
谢谢您的帮助。
它的工作原理。非常感谢。 – Luji