JavaAndroid:SharedReferences。如何正确地实施它们

Question

我试图将用户条目存储到EditText字段中，但是当我退出应用程序时，它不会出现

例如，一个用户输入他/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。但是我不能让它工作。我相信这与共享参考有关，但我不确定我错在哪里

我对安卓和java还很陌生，所以发现这很难。任何帮助都将不胜感激

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);
    }

第二项活动

 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中存储值之后，必须将其保存在SharedReference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.

然后在启动应用程序时，需要从SharedReferences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

Answer 2

您正在使用onSaveInstanceState()和onRestoreInstanceState()保存和恢复EditText的内容。但是，只有当操作系统终止应用程序并立即重新创建（即设备旋转）时，才会调用此方法

如果您希望在用户终止应用程序时保留值，则需要将其存储在某个位置、文件、数据库，或者在您的情况下，我建议您使用SharedReference

我在SharePreferences上发布了一个类似问题的答案

祝你好运