如何将结果从asynctask返回到Android中的活动？

Question

I have created a Login activity which uses another class - LoginService which is an AsyncTask for the network communication.

 public void onClick(View view) {

            if (editTextPassword.getText().toString() != null & editTextUsername.getText().toString() != null){

                new LoginService(editTextUsername.getText().toString(), editTextPassword.getText().toString()).execute();

                if(loginSuccess!=false){
                //Used to move to the Cases Activity
                Intent casesActivity = new Intent(getApplicationContext(), CasesActivity.class);
                startActivity(casesActivity);
                }else{
                    Toast.makeText(getApplicationContext(),"Incorrect Details", Toast.LENGTH_LONG).show();
                }
             }
            else{
                //Display Toaster for error
                Toast.makeText(getApplicationContext(),"Please enter your details", Toast.LENGTH_LONG).show();
            }
        }

Before the LoginService has finished executing, the activity has already moved to another activity via the Intent variable. I do not understand why. The idea of the LoginService is to validate the credentials of the user. If it returns true, then it can switch to the other activity.

Answer 1

You do not want to do this in this way. The .execute() will begin as soon as possible, but there is no guarantee (and perhaps guaranteed not to) that it will get your loginSuccess value back to you in time.

Everything after new LoginService(...).execute(); should be moved into onPostExecute() :

private Context mContext = null;
public void setContext(Context context) {
    mContext = context;
}
@Override
protected void onPostExecute(Void result) {
    if(loginSuccess!=false){
        //Used to move to the Cases Activity
        Intent casesActivity = new Intent(mContext, CasesActivity.class);
        startActivity(casesActivity);
    }else{
        Toast.makeText(mContext,"Incorrect Details", Toast.LENGTH_LONG).show();
    }
}

Then, you have to call setContext() like so:

LoginService service = new LoginService(editTextUsername.getText().toString(), editTextPassword.getText().toString());
service.setContext(getApplicationContext());
service.execute();

Answer 2

You should move

Intent casesActivity = new Intent(getApplicationContext(), CasesActivity.class);
            startActivity(casesActivity);
            }else{
                Toast.makeText(getApplicationContext(),"Incorrect Details",     Toast.LENGTH_LONG).show();
            }

into LoginService's onPostExecute.

In this way you are sure the asynctask has finished its work.

In any case it's quite strange the other activity gets started, it might be because of an old assignement of loginSuccess to true

Answer 3

How to return the result from the asynctask?

Catch the result of AsyncTask from onPostExecute() .

@Override
public void onPostExecute(Boolean result)
{
    boolean loginSuccess = result;

    if(loginSuccess!=false) { 

         Intent casesActivity = new Intent(getApplicationContext(), CasesActivity.class);
         startActivity(casesActivity);
    }
    else {

        Toast.makeText(getApplicationContext(),"Incorrect Details", Toast.LENGTH_LONG).show();
    }

}

The data type of result in AsyncTask depends on the 3rd Type parameter.

Sometimes we think execute() method of AsyncTask will return a result which is wrong. It will return an AsyncTask itself