java - Android:共享首选项。如何正确实现它们

Question

我正在尝试将用户条目存储到 EditText 字段中，但是当我退出应用程序时，它不会出现。

例如，用户输入他/她的名字，然后退出应用程序。当用户返回并启动应用程序时，用户名将显示在 EditText 字段中。但是我无法让它发挥作用。我相信它与共享首选项有关，但我不确定我哪里出错了。

我对 android 和 java 很陌生，所以发现这很困难。任何帮助将不胜感激。

public class MainActivity extends Activity {
     public final static String EXTRA_FROM = "com.example.assignment1.FROM";


     @Override
        protected void onSaveInstanceState(Bundle outState)
        {
            super.onSaveInstanceState(outState);
            EditText emailFrom =(EditText) findViewById(R.id.editEmailFrom);
            String from = emailFrom.getText().toString();
            outState.putString(EXTRA_FROM, from);
        }

        @Override
        protected void onRestoreInstanceState(Bundle savedState)
        {

            EditText emailFrom =(EditText) findViewById(R.id.editEmailFrom);
            String from = savedState.getString(EXTRA_FROM);
            emailFrom.setText(from);

        }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.activity_main, menu);
        return true;
    }

    public void emailSend (View sendButton) 
    {
        Intent intent = new Intent(this,DisplayEmailActivity.class);

        EditText emailFrom =(EditText) findViewById(R.id.editEmailFrom);
        String from = emailFrom.getText().toString();
        intent.putExtra(EXTRA_FROM,from);

        SharedPreferences saveFrom = getSharedPreferences(EXTRA_FROM, MODE_PRIVATE);
        Editor editor = saveFrom.edit();
        editor.putString(EXTRA_FROM, from);
        editor.commit();

        String storedfrom = saveFrom.getString(EXTRA_FROM, from);
        emailFrom.setText(storedfrom);

        startActivity(intent);
    }

第二个 Activity

 public class DisplayEmailActivity extends Activity {

        @Override
        public void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_display_email);

            Intent intent = getIntent();

            String from = intent.getStringExtra(MainActivity.EXTRA_FROM);
            TextView textFrom =(TextView)findViewById(R.id.displayEmailFrom);
            textFrom.setText(from);

        }

        @Override
        public boolean onCreateOptionsMenu(Menu menu) {
            getMenuInflater().inflate(R.menu.activity_display_email, menu);
            return true;
        }

Answer 1

好的，在 EditText emailFrom 中存储值后，您必须将其保存在 SharedPreferences 中，如下所示:

String from = emailFrom.getText().toString(); // Getting String value from EditText and storing it in "from" String
SharedPreferences settings = getSharedPreferences("MyPreferencesFile", 0); // Opening SharedPreferences 
SharedPreferences.Editor editor = settings.edit(); // Opening editor for SharedPreferences
editor.putString("exampleName", from); // You are putting here a String "from" and give it a "exampleName" name. Later you will use this name to restore data.

然后当您启动应用程序时，您需要从 SharedPreferences 加载数据:

SharedPreferences settings = getSharedPreferences("MyPreferencesFile", 0); // Again opening SharedPreferences
String from = settings.getString("exampleName", ""); // The second argument is the default value. The default value will be set if there wasn't saved any data with "exampleName" name
if(from != "") // If "from" is not empty, it means that the data was stored in SharedPreferences
   emailFrom.setText(from); // Setting text in your EditText