使用数据绑定添加BottomNavigationView的点击事件监听器

Question

我想使用数据绑定库来更改工具栏标题。除底部导航视图的监听器外，一切正常，即我遇到了错误：

FAILURE: Build failed with an exception.

* What went wrong:
Execution failed for task ':app:compileDebugJavaWithJavac'.
> java.lang.RuntimeException: Found data binding errors.
****/ data binding error ****msg:Could not resolve viewmodel::onNavigationClick as a listener.
file:D:\Replacements\app\src\main\res\layout\activity_main.xml
loc:85:40 - 85:67
****\ data binding error ****

我认为这是由于使用了错误的setter名称来关联xml属性所致。在xml中，BottomNavigationView有app:onNavigationItemSelected，但BottomNavigationView的setter是setOnNavigationItemSelectedListener，而不是setOnNavigationItemSelected。如果我是正确的，解决方案在Android文档中。但是我应该把这些注释放在哪里？在哪个类中？

换句话说，我应该怎么做才能在ViewModel中编写代码，以便我可以控制对BottomNavigationView的单击？

以下是文件：

ActivityMain.java

public class ActivityMain extends AppCompatActivity {

    private ActivityMainViewModel viewModel;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        // Initiating ViewModel to Activity
        viewModel = ViewModelProviders.of(this).get(ActivityMainViewModel.class);

        // Initiating ContentView in Activity
        setContentView(R.layout.activity_main);

        // Initiating DataBinding for ContentView in Activity
        ActivityMainBinding binding = DataBindingUtil.setContentView(this, R.layout.activity_main);
        binding.setViewmodel(viewModel);
    }
}

ActivityMainViewModel.java

public class ActivityMainViewModel extends ViewModel {

    private MutableLiveData<String> toolbarTitle = new MutableLiveData<>();

    public String getToolbarTitle() {
        return toolbarTitle.getValue();
    }

    public void setToolbarTitle(String toolbarTitle) {
        this.toolbarTitle.setValue(toolbarTitle);
    }

    public boolean onNavigationClick(@NonNull MenuItem item) {
        switch (item.getItemId()) {
            case R.id.navigation_1:
                setToolbarTitle("title 1");
                return true;
            case R.id.navigation_2:
                setToolbarTitle("title 2");
                return true;
            case R.id.navigation_3:
                setToolbarTitle("title 3");
                return true;
        }
        return false;
    }
}

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<layout xmlns:android="http://schemas.android.com/apk/res/android">

<data>
    <variable name="viewmodel" type="com.example.example.viewmodel.ActivityMainViewModel"/>
</data>

<android.support.constraint.ConstraintLayout
    ...>

    <android.support.design.widget.AppBarLayout
        ...>

        <android.support.v7.widget.Toolbar
            android:id="@+id/main_toolbar"
            android:title="@{viewmodel.toolbarTitle}"
            android:layout_width="match_parent"
            android:layout_height="?attr/actionBarSize"
            android:background="@color/new_blue_light"
            android:minHeight="?attr/actionBarSize"
            android:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar"
            app:popupTheme="@style/ThemeOverlay.AppCompat.Light" />

    </android.support.design.widget.AppBarLayout>

    <FrameLayout
        ...>
        ...
    </FrameLayout>

    <android.support.design.widget.BottomNavigationView
        android:id="@+id/navigation"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:background="?android:attr/windowBackground"
        app:itemIconTint="@drawable/navigation_color_state"
        app:itemTextColor="@drawable/navigation_color_state"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:menu="@menu/navigation"
        app:onNavigationItemSelected="@{viewmodel::onNavigationClick}"
        tools:layout_constraintBottom_creator="0"
        tools:layout_constraintLeft_creator="0"
        tools:layout_constraintRight_creator="0" />

</android.support.constraint.ConstraintLayout>

</layout>

我尝试做的唯一一件事就是创建自定义视图（应用程序可以运行，但它不会更改工具栏标题，并显示警告：warning: Application namespace for attribute app:onNavigationItemSelected will be ignored.）：

@BindingMethods({
        @BindingMethod(
                type = BottomNavigationViewBinding.class,
                attribute = "app:onNavigationItemSelected",
                method = "setOnNavigationItemSelectedListener"
        ),
})
public class BottomNavigationViewBinding extends BottomNavigationView{

    private OnNavigationItemSelectedListener mSelectedListener;

    public BottomNavigationViewBinding(Context context) {
        this(context, null);
    }

    public BottomNavigationViewBinding(Context context, AttributeSet attrs) {
        this(context, attrs, 0);
    }

    public BottomNavigationViewBinding(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
    }

    public interface OnNavigationItemSelectedListener {
        boolean onNavigationItemSelected(MenuItem item);
    }

    public void setOnNavigationItemSelectedListener(@Nullable OnNavigationItemSelectedListener listener) {
        mSelectedListener = listener;
    }
}

- Dawid Tarasiuk

Answer 1

请使用以下代码替换您的NavigationItemViewBinding类，然后它将正常工作：

public class BottomNavigationViewBindingAdapter {
    @BindingAdapter("onNavigationItemSelected")
    public static void setOnNavigationItemSelectedListener(
            BottomNavigationView view, OnNavigationItemSelectedListener listener) {
        view.setOnNavigationItemSelectedListener(listener);
    }
}

这个想法是你想使用自定义setter来整合监听器，这需要比重命名设置监听器的方法更多的工作。

https://developer.android.com/topic/libraries/data-binding/index.html#custom_setters

- Uli

---

把这个类放在哪里？ - suv