我意识到这是一个老问题，但我想提供一个解决方案，以便它可以帮助其他人解决同样的问题。这可以使用菜单项的操作视图来实现。它需要相当多的代码，但它是一种使用 MVVM 的方法，可用于任何数据绑定。
这是一个图标显示计数并在计数大于 0 时更改背景的示例。
定义菜单项
menu/main.xml
<?xml version="1.0" encoding="utf-8"?>
<menu xmlns:android="http://schemas.android.com/apk/res/android">
<item
android:id="@+id/action_count"
android:enabled="true"
android:icon="@drawable/ic_menu_red_square"
android:title="@string/count"/>
</menu>
定义菜单项的视图模型。
public class CountMenuViewModel extends BaseObservable {
@Bindable
int count;
public CountMenuViewModel() {}
public int getCount() {
return count;
}
public void setCount(int count) {
this.count = count;
if (this.count < 0) {
this.count = 0;
}
notifyPropertyChanged(BR.count);
}
@Bindable({"count"})
public @DrawableRes int getBackground() {
if (count > 0) {
return R.drawable.ic_menu_blue_square;
}
return R.drawable.ic_menu_red_square;
}
@Bindable({"count"})
public String getCountText() {
if (count > 0) {
return String.valueOf(count);
}
return null;
}
}
定义一个回调，当点击菜单项时，Activity 将执行该回调。
public interface CountMenuActionCallback {
void onCountMenuItemClicked();
}
为动作视图创建一个布局。布局使用视图模型类并为计数和背景设置文本。回调接口用于动作视图的 OnClickListener。
layout/menu_action_count.xml
<?xml version="1.0" encoding="utf-8"?>
<layout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools">
<data>
<variable
name="data"
type="com.botnerd.samplesapp.CountMenuViewModel"
/>
<variable
name="callback"
type="com.botnerd.samplesapp.CountMenuActionCallback"
/>
</data>
<FrameLayout
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:onClick="@{() -> callback.onCountMenuItemClicked()}"
android:background="?android:attr/actionBarItemBackground">
<ImageView
android:layout_width="32dp"
android:layout_height="32dp"
android:layout_margin="4dp"
android:src="@{data.background}"
tools:src="@drawable/ic_menu_red_square"
/>
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center"
android:text="@{data.countText}"
tools:text="30"
android:textSize="14dp"
android:maxLines="1"
android:textColor="@android:color/white"
tools:ignore="SpUsage"/>
</FrameLayout>
</layout>
请注意，自定义绑定适配器用于android:src 属性。这是一个通过数据绑定设置 ImageView src 的好适配器。
@BindingAdapter({"android:src"})
public static void setSrc(ImageView view, @DrawableRes int resId) {
try {
view.setImageDrawable(ContextCompat.getDrawable(view.getContext(), resId));
} catch (Resources.NotFoundException e) {
}
}
最后，膨胀菜单并在活动中绑定动作视图布局。
@Override
public boolean onCreateOptionsMenu(Menu menu) {
getMenuInflater().inflate(R.menu.main, menu);
MenuItem menuItemCount = menu.findItem(R.id.action_count);
MenuActionCountBinding binding = MenuActionCountBinding.inflate(getLayoutInflater());
binding.setData(mCountMenuViewModel);
binding.setCallback(mCountMenuActionCallback);
MenuItemCompat.setActionView(menuItemCount, binding.getRoot());
MenuItemCompat.setShowAsAction(menuItemCount, MenuItemCompat.SHOW_AS_ACTION_ALWAYS);
return super.onCreateOptionsMenu(menu);
}
为了完整起见，这里列出了示例中未在上面定义的所有文件。
drawable/ic_menu_blue_square.xml
<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android">
<padding android:bottom="4dp"
android:left="4dp"
android:right="4dp"
android:top="4dp"/>
<solid android:color="#000080"/>
<corners android:radius="2dp"/>
</shape>
drawable/ic_menu_red_square.xml
<shape xmlns:android="http://schemas.android.com/apk/res/android">
<padding android:bottom="4dp"
android:left="4dp"
android:right="4dp"
android:top="4dp"/>
<solid android:color="#800000"/>
<corners android:radius="2dp"/>
</shape>
layout/activity_main.xml
<?xml version="1.0" encoding="utf-8"?>
<layout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools">
<data>
<variable
name="callback"
type="com.botnerd.samplesapp.MainActivityActionCallback"
/>
</data>
<android.support.constraint.ConstraintLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="com.botnerd.samplesapp.MainActivity">
<Button
android:id="@+id/button"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="-"
android:onClick="@{() -> callback.onMinusClicked()}"
android:layout_marginStart="79dp"
app:layout_constraintBaseline_toBaselineOf="@+id/button2"
tools:layout_constraintBaseline_creator="1"
tools:layout_constraintLeft_creator="1"
app:layout_constraintLeft_toLeftOf="parent"/>
<Button
android:id="@+id/button2"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="+"
android:onClick="@{() -> callback.onPlusClicked()}"
tools:layout_constraintTop_creator="1"
android:layout_marginStart="25dp"
android:layout_marginTop="97dp"
tools:layout_constraintLeft_creator="1"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintLeft_toRightOf="@+id/button"/>
</android.support.constraint.ConstraintLayout>
</layout>
MainActivityActionCallback.java
public interface MainActivityActionCallback {
void onPlusClicked();
void onMinusClicked();
}
MainActivity.java
public class MainActivity extends AppCompatActivity {
ActivityMainBinding mBinding;
CountMenuViewModel mCountMenuViewModel;
CountMenuActionCallback mCountMenuActionCallback = new CountMenuActionCallback() {
@Override
public void onCountMenuItemClicked() {
Toast.makeText(MainActivity.this, "Count clicked!", Toast.LENGTH_SHORT)
.show();
}
};
MainActivityActionCallback mActionCallback = new MainActivityActionCallback() {
@Override
public void onPlusClicked() {
mCountMenuViewModel.setCount(mCountMenuViewModel.getCount() + 1);
}
@Override
public void onMinusClicked() {
mCountMenuViewModel.setCount(mCountMenuViewModel.getCount() - 1);
}
};
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
mCountMenuViewModel = new CountMenuViewModel();
mBinding = DataBindingUtil.setContentView(this, R.layout.activity_main);
mBinding.setCallback(mActionCallback);
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
getMenuInflater().inflate(R.menu.main, menu);
MenuItem menuItemCount = menu.findItem(R.id.action_count);
MenuActionCountBinding binding = MenuActionCountBinding.inflate(getLayoutInflater());
binding.setData(mCountMenuViewModel);
binding.setCallback(mCountMenuActionCallback);
MenuItemCompat.setActionView(menuItemCount, binding.getRoot());
MenuItemCompat.setShowAsAction(menuItemCount, MenuItemCompat.SHOW_AS_ACTION_ALWAYS);
return super.onCreateOptionsMenu(menu);
}
}