java - 当我启动新 Activity 时，为什么我的 SharedPreferences 无法检索到正确的数据？

Question

我有两个 Activity LoginActivity 和 MainActivity，我从 LoginActivity 验证我的用户。如果用户身份验证成功，我将使用 MainActivity Intent 调用 startActivity()。 LoginActivity 如下所示:

在我的 onCreate() 中，我初始化了已声明为类字段的 SharedPreferences 对象:

 userInfo = PreferenceManager.getDefaultSharedPreferences(getApplicationContext());
 editor = userInfo.edit();

然后我在 login() 方法中处理身份验证逻辑:

private void login() {


    progressDialog.setIndeterminate(true);
    progressDialog.setMessage("Authenticating...");
    progressDialog.show();

    final String email = emailText.getText().toString();
    final String password = passwordText.getText().toString();


    new android.os.Handler().postDelayed(new Runnable() {

        public void run() {
            ref.authWithPassword(email, password, new Firebase.AuthResultHandler({      

            // User was authenticated successfully
            @Override
            public void onAuthenticated(AuthData authData) {

              @Override
              public void onDataChange(DataSnapshot snapshot) {
              UserSchema user = snapshot.getValue(UserSchema.class);

                // store the user's name and email with our SharedPreferences
                 editor.putString("name", user.getName());
                 editor.putString("email", user.getEmail());
                 editor.apply();
               }  
          });

         // Dismiss the progress dialog shown while authenticating the user
         progressDialog.dismiss();

      // Start the MainActivity
      Intent intent = new Intent(getApplicationContext(), MainActivity.class);
      startActivity(intent); 
      }
    }
      }, 3000);
   }

我还在 MainActivity 的 onCreate() 中初始化 PreferenceManager:

  userInfo = PreferenceManager.getDefaultSharedPreferences(getApplicationContext());

<小时/>

一开始一切正常，但是当 MainActivity 启动时，所有获取存储的用户信息的调用都会返回我在 MainActivity 类中设置的默认值:

  // returns the default value at first
  String s1 = userInfo.getString("name", "name"); 
  String s2 = userInfo.getString("email", "email");

Weird part: If I close the app from my device's recents and relaunch it, the right values of the user's name and email show up correctly.

Answer 1

请注意，onDataChange 是一个回调，它不会立即被调用，但 startActivity 会在调用此回调之前被调用。因此，在数据保存到 SharedPreference 之前调用 MainActivity。

代码应该是这样的

private void login() {
    ...
    // User was authenticated successfully
    @Override
    public void onDataChange(DataSnapshot snapshot) {
        UserSchema user = snapshot.getValue(UserSchema.class);

        // store the user's name and email with our SharedPreferences
        editor.putString("name", user.getName());
        editor.putString("email", user.getEmail());
        editor.apply();

        // Start the MainActivity
        Intent intent = new Intent(getApplicationContext(), MainActivity.class);
        startActivity(intent);
    } 
}