我有一个单独的AsyncTask类，它会执行一些耗时的任务。从活动中调用AsyncTask时，将启动进度对话框。如果用户取消对话框或在执行后台任务时发生错误，则沿着该行被解雇。如果后台进程成功，则应该运行verifyingUser方法，即主Activity。这就是我的问题所在。这是我的代码：
public class CreateAccountTask extends AsyncTask<String, Void, String>{
private ProgressDialog mpDialog;
private CreateAccountTask task;
private Context context;
private Activity activity;
private CreateAccount createAccount;
private AsyncTaskListener asyncTaskListener;
public CreateAccountTask(Activity activity, AsyncTaskListener asyncTaskListener){
this.activity = activity;
this.asyncTaskListener = asyncTaskListener;
}
@Override
protected void onPreExecute() {
// TODO Auto-generated method stub
super.onPreExecute();
mpDialog = new ProgressDialog(activity);
//mpDialog.setTitle("Creating Account");
mpDialog.setMessage("Please wait.");
mpDialog.setCancelable(false);
mpDialog.setIndeterminate(false);
mpDialog.setButton(DialogInterface.BUTTON_NEGATIVE, "CANCEL", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface arg0, int arg1) {
// TODO Auto-generated method stub
//task.cancel(true);
mpDialog.dismiss();
}
});
mpDialog.show();
}
@Override
protected String doInBackground(String... arg0) {
// TODO Auto-generated method stub
String fphoneNo = arg0[1];
String fpassword = arg0[0];
// create instance of the parseUser Class
ParseUser newUser = new ParseUser();
newUser.setUsername(fphoneNo);
newUser.setPassword(fpassword);
// here Check if progress dialog has been cancelled
if (!isCancelled()){
// if dialog has not been cancelled create the new user here
newUser.signUpInBackground(new SignUpCallback() {
@Override
public void done(ParseException e) {
// Something went wrong Sorry!
if(e != null ){
if(!isCancelled()){
mpDialog.dismiss();
String errorMessage = e.getMessage().toString();
ErrorHappened(errorMessage);
}
else{
String errorMessage = "Registration Cancelled!";
ErrorHappened(errorMessage);
}
}
// No Problems
else {
if (!isCancelled()) {
// Wait for five seconds before starting the activity
//verifyingUser();
}
else {
String errorMessage = "Registration Cancelled2!";
ErrorHappened(errorMessage);
//Delete user in background
ParseUser currentUser = ParseUser.getCurrentUser();
if (currentUser != null) {
currentUser.deleteInBackground();
}
}
}
}
});
}
return null;
}
@Override
protected void onPostExecute(String result) {
// TODO Auto-generated method stub
super.onPostExecute(result);
asyncTaskListener.onTaskComplete(result);
}
private void ErrorHappened(String errorMessage) {
Crouton CreateMagic = Crouton.makeText(createAccount, errorMessage, CroutonClass.ALERT);
CreateMagic.setConfiguration(CroutonClass.configure);
CreateMagic.show();
}
}
这是我的主要活动，我在调用verifyingUser方法时尝试关闭进度对话框：
public class CreateAccount extends ActionBarActivity implements AsyncTaskListener {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_create_account);
mPassWord = (EditText) findViewById(R.id.password);
mcreateAccount = (Button) findViewById(R.id.createAcct);
mPhoneNumber = (EditText) findViewById(R.id.Phone_Number);
// create account Method
createAccount();
}//end of on create.
public void createAccount() {
mcreateAccount.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View arg0) {
CreateAccountTask newTask = new CreateAccountTask(CreateAccount.this, new CreateAccount());
newTask.execute(passwordString, fpartphoneNo);
});
}
private void verifyingUser() {
ok();
}
protected void ok() {
// TODO Auto-generated method stub
CreateAccountTask.mpDialog.dismiss();
Intent nextPage = new Intent(getBaseContext(), VerifyAccount.class);
startActivity(nextPage);
}
@Override
public void onBackPressed() {
// TODO Auto-generated method stub
Crouton.cancelAllCroutons();
super.onBackPressed();
}
@Override
public void onTaskComplete(String result) {
// TODO Auto-generated method stub
}
}
我在尝试关闭对话框时遇到此异常：
03-05 13:43:32.839: E/AndroidRuntime(21782): FATAL EXCEPTION: main
03-05 13:43:32.839: E/AndroidRuntime(21782): java.lang.NullPointerException
03-05 13:43:32.839: E/AndroidRuntime(21782): at android.content.ComponentName.<init> (ComponentName.java:75)
03-05 13:43:32.839: E/AndroidRuntime(21782): at android.content.Intent.<init>(Intent.java:3655)
03-05 13:43:32.839: E/AndroidRuntime(21782): at com.example.razcat.CreateAccount.ok(CreateAccount.java:527)
03-05 13:43:32.839: E/AndroidRuntime(21782): at com.example.razcat.CreateAccount$3.done(CreateAccount.java:480)
03-05 13:43:32.839: E/AndroidRuntime(21782): at com.example.razcat.CreateAccount$3.done(CreateAccount.java:1)
03-05 13:43:32.839: E/AndroidRuntime(21782): at com.parse.FunctionCallback.internalDone(FunctionCallback.java:44)
03-05 13:43:32.839: E/AndroidRuntime(21782): at com.parse.Parse$6$1.run(Parse.java:834)
03-05 13:43:32.839: E/AndroidRuntime(21782): at android.os.Handler.handleCallback(Handler.java:615)
03-05 13:43:32.839: E/AndroidRuntime(21782): at android.os.Handler.dispatchMessage(Handler.java:92)
03-05 13:43:32.839: E/AndroidRuntime(21782): at android.os.Looper.loop(Looper.java:155)
03-05 13:43:32.839: E/AndroidRuntime(21782): at android.app.ActivityThread.main(ActivityThread.java:5454)
03-05 13:43:32.839: E/AndroidRuntime(21782): at java.lang.reflect.Method.invokeNative(Native Method)
03-05 13:43:32.839: E/AndroidRuntime(21782): at java.lang.reflect.Method.invoke(Method.java:511)
03-05 13:43:32.839: E/AndroidRuntime(21782): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1029)
03-05 13:43:32.839: E/AndroidRuntime(21782): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:796)
03-05 13:43:32.839: E/AndroidRuntime(21782): at dalvik.system.NativeStart.main(Native Method)
如何从verifyingUser方法中删除对话框？
答案 0 :(得分：0)
您正在尝试修改工作线程中的UI组件。您必须在onPostExecute或主线程中执行此操作。你可以做的是取消任务或返回null或一些标志值，然后解除onPostExecute。