以编程方式将子菜单添加到菜单项 - Android

Question

我试图以编程方式将一个SubMenu添加到我的MenuItem,我该怎么做？到目前为止这是我的代码:

    @Override
public boolean onCreateOptionsMenu(Menu menu) {

    menu.add(Menu.NONE, R.id.extra_options, Menu.NONE, "Menu1")
    .setIcon(Config.chooseActionBarIcon(
            MainActivity.this, "ic_actionbar_font"))
    .setShowAsAction(MenuItem.SHOW_AS_ACTION_ALWAYS);

    SubMenu themeMenu = menu.findItem(R.id.extra_options).getSubMenu();
    themeMenu.clear();
    themeMenu.add(0, R.id.theme_auto, Menu.NONE, "Automatic");
    themeMenu.add(0, R.id.theme_day, Menu.NONE, "Default");
    themeMenu.add(0, R.id.theme_night, Menu.NONE, "Night");
    themeMenu.add(0, R.id.theme_batsave, Menu.NONE, "Battery Saving");


    return super.onCreateOptionsMenu(menu);
}

R.id.extra_options是在"ids.xml"资源文件中定义的ID;

<item type="id" name="extra_options" />

使用getSubMenu()获取SubMenu似乎没问题,但是当我尝试将项添加到SubMenu时,我收到错误"NullPointerException"

任何人都知道代码有什么问题？

Answer 1

您可以将"menu.add"替换为"menu.addSubMenu"我认为这会对您有所帮助

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.single_product, menu);

    menu.addSubMenu(Menu.NONE, R.id.extra_options, Menu.NONE,"Menu1");

     SubMenu themeMenu = menu.findItem(R.id.extra_options).getSubMenu();

     themeMenu.clear();
     themeMenu.add(0, R.id.theme_auto, Menu.NONE, "Automatic");
     themeMenu.add(0, R.id.theme_day, Menu.NONE, "Default");
     themeMenu.add(0, R.id.theme_night, Menu.NONE, "Night");
     themeMenu.add(0, R.id.theme_batsave, Menu.NONE, "Battery Saving");

    return true;
}

Answer 2

Try adding empty menu tag into your menu item. Like this:

<item
  android:id="@+id/menu_common_object"
  android:title="@string/menu_common_object">
  <menu></menu>
</item>

After this

menuItem.getSubMenu().add(..)

will work fine at runtime.