我有一个应用程序，其中一个活动使用AsyncTask从另一个类中调用一个方法，该类连接到数据库以改变用户的登录凭据。 Activity EntryActivity有三个成员变量需要使用AsyncTask，carerID，firstName和surName的结果进行更新。当我第一次运行应用程序时，所有三个变量都为空，但如果我第二次按下登录按钮，变量设置正确，应用程序的行为应该如此。
在第一次运行应用程序时，有没有理由从onPostxecute中正确设置三个成员变量？
public class EntryActivity extends NfcBaseActivity{
private LoginWebservice loginWebservice;
private static final String TAG = EntryActivity.class.getSimpleName();
private Button login;
private EditText userName;
private EditText passwordPin;
NfcScannerApplication nfcscannerapplication;
public static final String CUSTOM_QRCODE_ACTION = "com.carefreegroup.QRCODE_ACTION";
private String carerID;
private String firstName;
private String surName;
private boolean isValidated = false;
@Override
protected void onCreate(final Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.entryscreen);
nfcscannerapplication = (NfcScannerApplication) getApplication();
loginWebservice = new LoginWebservice(this);
carerID = null;
firstName = null;
surName = null;
userName = (EditText)findViewById(R.id.username);
passwordPin = (EditText)findViewById(R.id.password);
login = (Button)findViewById(R.id.buttonlogin);
login.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
////////////get user's input///////////
String compId = "100";
String theUsername = userName.getText().toString();
String thePassword = passwordPin.getText().toString();
String loginType = "1";
String[] params = new String[]{compId, theUsername, thePassword, loginType};
//validate user Asynchonously on background thread
new AsyncValidateCarer().execute(params);
Log.e(TAG, "carerid =" + carerID + " firstname = " + firstName + " surnamee = " + surName);
DateTime now = new DateTime();
long loginTime = now.getMillis();
String fullName = firstName +" " + surName;
Log.e(TAG, "fullname = " + fullName);
if(carerID != null){
ContentValues loginValues = new ContentValues();
loginValues.putNull(LoginValidate.C_ID_INDEX);
loginValues.put(LoginValidate.C_CARER_ID, carerID);
loginValues.put(LoginValidate.C_COMP_ID, compId);
loginValues.put(LoginValidate.C_CARER_NAME, fullName);
loginValues.put(LoginValidate.C_PASSWORD, thePassword);
loginValues.put(LoginValidate.C_DATE_TIME, loginTime);
nfcscannerapplication.loginValidate.insertIntoCarer(loginValues);
Toast.makeText(
EntryActivity.this,
"Carer logged in to System",
Toast.LENGTH_LONG).show();
isValidated = true;
Intent intent = new Intent(EntryActivity.this,
NfcscannerActivity.class);
intent.setAction(CUSTOM_QRCODE_ACTION);
startActivity(intent);
}else{
Toast.makeText(
EntryActivity.this,
"Please check credentials",
Toast.LENGTH_LONG).show();
}
//////////////validate user/////////////////
}
});
Button changeUser = (Button)findViewById(R.id.buttonchangeuser);
changeUser.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
Log.e(TAG, "change user button clicked");
nfcscannerapplication.loginValidate.deleteTableCarer();
Toast.makeText(
EntryActivity.this,
"Carer logged out",
Toast.LENGTH_LONG).show();
EntryActivity.this.onCreate(savedInstanceState);
}
});
}//end of onCreate
private void hideSoftKeyboard() {
InputMethodManager imm = (InputMethodManager) getSystemService(Context.INPUT_METHOD_SERVICE);
imm.hideSoftInputFromWindow(passwordPin.getWindowToken(), 0);
}
private class AsyncValidateCarer extends AsyncTask<String, Void, ContentValues> {
@Override
protected ContentValues doInBackground(String... params) {
ContentValues cv = null;
try {
Log.e(TAG, "inside asynctask");
cv = loginWebservice.validateCarer(params[0], params[1], params[2], params[3]);
if (cv != null){
Log.e(TAG, "cv = not null!");
}
} catch (Exception e) {
e.printStackTrace();
}
return cv;
}
@Override
protected void onPostExecute(ContentValues result) {
Log.e(TAG, "inside onpostexecute");
EntryActivity.this.carerID = (String) result.get("carerID");
EntryActivity.this.firstName = (String) result.get("firstname");
EntryActivity.this.surName = (String) result.get("surname");
}
}
}
[更新]
private class AsyncValidateCarer extends AsyncTask<String, Void, Void> {
@Override
protected Void doInBackground(String... params) {
ContentValues cv = null;
try {
Log.e(TAG, "inside doInBackground");
cv = loginWebservice.validateCarer(params[0], params[1], params[2], params[3]);
carerID = (String) cv.get("carerID");
firstName = (String) cv.get("firstname");
surName = (String) cv.get("surname");
if (cv != null){
Log.e(TAG, "cv = not null! and exiting doInBackground");
}
} catch (Exception e) {
e.printStackTrace();
}
return null;
}
}
答案 0 :(得分：1)
AsyncTask将异步执行，因此您无法保证在“执行”方法调用之后，该任务实际上已完成。我的建议是在“onPostExecute”方法中移动“执行”调用后的所有内容（或至少与这些字段相关的内容）。
第一次点击似乎不起作用，第二次点击的原因是，在第一次“登录”点击和第二次点击之间，你等待AsyncTask完成。因此，当您第二次单击时，您会看到第一次执行的结果。请在“onPostExecute”中添加一些“Log”信息，以了解发生了什么。
希望有所帮助:)
答案 1 :(得分：0)
carerID = null;
firstName = null;
surName = null;
从onCreate()方法移除上述语句，因为它们已经初始化为默认值，因为它们位于Class Scope中并被称为Instance Variables.