android - 如何在菜单上保存所选单选按钮的实例状态

Question

我的工具栏中有带有单选按钮项的选项菜单:

 <item
    android:id="@+id/map_menu"
    android:icon="@drawable/ic_layer"
    android:orderInCategory="102"
    app:showAsAction="always"
    android:title="@string/action_settings">
    <menu>
        <group
            android:id="@+id/map_types_group"
            android:checkableBehavior="single" >
            <item
                android:id="@+id/map_terrain"
                android:orderInCategory="1"
                app:showAsAction="ifRoom"
                android:title="@string/map_terrain"/>
            <item
                android:id="@+id/map_normal"
                android:orderInCategory="2"
                android:checked="true"
                app:showAsAction="ifRoom"
                android:title="@string/map_normal"/>
            <item
                android:id="@+id/map_hybrid"
                android:orderInCategory="3"
                app:showAsAction="ifRoom"
                android:title="@string/map_hybrid"/>
        </group>
    </menu>
</item>

我想在 onSaveInstanceState、onRestoreInstanceState 中发生方向更改时恢复选定的单选按钮，但我不明白如何从选项菜单中的单选组中获取选定的按钮。

Answer 1

这是一个完整的工作和测试示例。有了这段代码，无论您旋转屏幕多少次，当前选择的项目都会保留。

首先，创建这些实例变量来跟踪菜单的状态，并为您将保存在 Bundle 中的首选项命名:

private final static String MENU_SELECTED = "selected";
private int selected = -1;
MenuItem menuItem;

saveInstanceState() 方法应该保存当前选择的值:

@Override
public void onSaveInstanceState(Bundle savedInstanceState) {
    savedInstanceState.putInt(MENU_SELECTED, selected);
    super.onSaveInstanceState(savedInstanceState);
}

在 onOptionsItemSelected() 中更新当前选中的项目:

@Override
public boolean onOptionsItemSelected(MenuItem item) {

    int id = item.getItemId();

    if (id == R.id.action_settings) {
        Log.d("settings", "id: " + id);
        return true;
    }

    if (id == R.id.map_terrain){
        Log.d("menuitem", "terrain id: " + id);
        selected = id;
        item.setChecked(true);
        return true;
    }

    if (id == R.id.map_normal){
        Log.d("menuitem", "normal id: " + id);
        selected = id;
        item.setChecked(true);
        return true;
    }

    if (id == R.id.map_hybrid){
        Log.d("menuitem", "hybrid id: " + id);
        selected = id;
        item.setChecked(true);
        return true;
    }

    return super.onOptionsItemSelected(item);
}

在onCreate()中，如果保存的数据存在则加载:

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

    if (savedInstanceState != null){
        selected = savedInstanceState.getInt(MENU_SELECTED);
    }
}

然后在onCreateOptionsMenu()中重新选择之前选择的项目:

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    getMenuInflater().inflate(R.menu.menu_main, menu);

    if (selected == -1){
        return true;
    }

    switch (selected){
        case R.id.map_terrain:
            menuItem = (MenuItem) menu.findItem(R.id.map_terrain);
            menuItem.setChecked(true);
            break;

        case R.id.map_normal:
            menuItem = (MenuItem) menu.findItem(R.id.map_normal);
            menuItem.setChecked(true);
            break;

        case R.id.map_hybrid:
            menuItem = (MenuItem) menu.findItem(R.id.map_hybrid);
            menuItem.setChecked(true);
            break;
    }

    return true;
}