java - 在 Android 上启动 Activity 并共享数据

Question

我是 Android 编程新手，遇到了一个无法克服的问题。我使用 Android Studio 示例构建了一个 TabHost 应用程序。当用户按下按钮时，我想调用另一个打开设置页面的 Activity (我从 gui 创建了一个基本 Activity “MySettings”)。

问题 1:当 Activity 关闭时，MainActivity 重新运行 onCreate，所选选项卡返回到启动选项卡。有没有办法继续上次选择的选项卡？

调用代码为:

public void buttonPressed(View view) { 
Intent intent = new Intent(MainActivity.this,MySettings.class);
MainActivity.this.startActivity(intent);
}

问题 2:我无法在两个 Activity 之间共享数据:

主要 Activity :

public class MainActivity extends AppCompatActivity {

@Override
protected void onCreate(Bundle savedInstanceState) {
SharedPreferences sharedpreferences =     PreferenceManager.getDefaultSharedPreferences(this);
    SharedPreferences.Editor editor = sharedpreferences.edit();

}

我的设置:

public class MySettings extends AppCompatActivity {

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_settings_inr);
    Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);
    SharedPreferences sharedpreferences =   PreferenceManager.getDefaultSharedPreferences(this);

    sharedpreferences.edit().putInt("myvar",200);
    sharedpreferences.edit().apply();
    FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
    fab.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
                    .setAction("Action", null).show();
        }
    });
    getSupportActionBar().setDisplayHomeAsUpEnabled(true);
};

此代码运行，但当 MySettings Activity 关闭时，调用 Activity MainActivity 中的“myvar”不会更新。

public void setImage(){
    SharedPreferences sharedpreferences = PreferenceManager.getDefaultSharedPreferences(this);
    int cvt=sharedpreferences.getInt("myvar",0);
}

Answer 1

问题 1:

您应该将选定的选项卡索引保存在您的 Activity 中，以便当它返回时，您可以在调用 onCreate 时读取该索引并选择它。

问题2:

@Luis Miguel Sierra 关于 SharedPreference 的说法是正确的。

但是您可能希望“startActivityForResult”将数据传递回第一个 Activity 。

Starting another activity doesn't have to be one-way. You can also start another activity and receive a result back. To receive a result, call startActivityForResult() (instead of startActivity()).

For example, your app can start a camera app and receive the captured photo as a result. Or, you might start the People app in order for the user to select a contact and you'll receive the contact details as a result.

Of course, the activity that responds must be designed to return a result. When it does, it sends the result as another Intent object. Your activity receives it in the onActivityResult() callback.

更多信息: Getting a Result from an Activity