Android: 如何在获取 Google 令牌的异步任务上实现回调？

Question

我正在尝试在我的应用程序上实现 google 登录。我设法登录并存储令牌，但由于任务是异步的，我不知道它何时完成，所以我无法在进一步的方法中安全地使用令牌。如何向 onPostExecute 添加回调方法？

代码如下：

 @Override
public void onConnected(Bundle bundle) {
    // onConnected indicates that an account was selected on the device, that the selected
    // account has granted any requested permissions to our app and that we were able to
    // establish a service connection to Google Play services.
    Log.d(TAG, "onConnected:" + bundle);
    mShouldResolve = false;

    mAccountName = Plus.AccountApi.getAccountName(mGoogleApiClient);

    //HERE I RETRIEVE THE TOKEN AND NEED TO IMPLEMENT CALLBACK
    new RetrieveTokenTask().execute(mAccountName);


    // Show the signed-in UI
    Intent intent = new Intent(getActivity(), MainActivity.class);
    startActivity(intent);
}

@Override
public void onClick(View v) {

    if (v.getId() == R.id.sign_in_button) {
        onSignInClicked();
    }
}

private void onSignInClicked() {
    // User clicked the sign-in button, so begin the sign-in process and automatically
    // attempt to resolve any errors that occur.
    mShouldResolve = true;
    mGoogleApiClient.connect();

    // Show a message to the user that we are signing in.
    //mStatusTextView.setText(R.string.signing_in);
    Log.i("GoogleSignIn", "in progress");
}


private class RetrieveTokenTask extends AsyncTask<String, Void, String> {

    @Override
    protected String doInBackground(String... params) {
        String accountName = params[0];
        String scopes = "oauth2:profile email";
        String token = null;
        try {
            token = GoogleAuthUtil.getToken(getActivity().getApplicationContext(), accountName, scopes);
        } catch (IOException e) {
            Log.e(TAG, e.getMessage());
        } catch (UserRecoverableAuthException e) {
            //startActivityForResult(e.getIntent(), REQ_SIGN_IN_REQUIRED);
        } catch (GoogleAuthException e) {
            Log.e(TAG, e.getMessage());
        }
        return token;
    }

    @Override
    protected void onPostExecute(String token) {
        super.onPostExecute(token);
        Log.i("Token Value: ", token);
        //TODO : access token verifier https://developers.google.com/identity/sign-in/android/backend-auth
        accessToken = token;
    }
}

Answer 1

你可以在 onPostExecute 方法中启动 main activity .. 这样你就可以确定任务已经执行并且即将完成。

检查这个

private class RetrieveTokenTask extends AsyncTask<String, Void, String> {

 private Callback callback;

public RetrieveTokenTask(Callback callback){
     this.callback = callback;
}

@Override
protected String doInBackground(String... params) {
    String accountName = params[0];
    String scopes = "oauth2:profile email";
    String token = null;
    try {
        token = GoogleAuthUtil.getToken(getActivity().getApplicationContext(), accountName, scopes);
    } catch (IOException e) {
        Log.e(TAG, e.getMessage());
    } catch (UserRecoverableAuthException e) {
        //startActivityForResult(e.getIntent(), REQ_SIGN_IN_REQUIRED);
    } catch (GoogleAuthException e) {
        Log.e(TAG, e.getMessage());
    }
    return token;
}

@Override
protected void onPostExecute(String token) {
    super.onPostExecute(token);
    Log.i("Token Value: ", token);
    //TODO : access token verifier https://developers.google.com/identity/sign-in/android/backend-auth
    accessToken = token;
    callback.done();
}

}

//create an interface
public interface Callback{
  //create the callback method
   void done();
}

启动任务时，像这样在构造函数中传递回调接口的实例，例如

new RetrieveTokenTask(this).execute(mAccountName);

并使您的 activity 实现回调接口。例如MainActivity implements Callback

现在 MainActivity 将有一个 done 方法，这个方法就是你的回调。

我希望这个解释对您有所帮助。

Answer 2

不要在 Android 上使用 AsyncTask。这很糟糕，真的很糟糕。您将开始出现内存泄漏，这很糟糕。

这里有更多信息说明为什么 AsyncTask 在 Android 上不好：http://simonvt.net/2014/04/17/asynctask-is-bad-and-you-should-feel-bad/

为了您的网络通话，为什么要重新发明轮子？有许多成熟且经过测试的库可以为您完成所有艰苦的工作，它们甚至可以为您提供回调。

我向您推荐 Square 的 Retrofit，它们为您提供同步调用以及异步（回调）和可观察对象。只需选择您想要的那个，最有可能是带有回调的异步。

Android: 如何在获取 Google 令牌的异步任务上实现回调？

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