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我用底部导航栏替换了抽屉导航，发现我不能再使用动作视图，这就是为什么我使用 LayerDrawables 作为我的图标的原因。

final Menu menu = bottomNavigationView.getMenu();

notificationBullet = new NotificationDotDrawable(Color.Red, false, this);
final MenuItem nav = menu.findItem(R.id.nav_overview);
final LayerDrawable navMutate = (LayerDrawable) nav.getIcon().mutate();
navMutate.setDrawableByLayerId(R.id.ic_menu_upcoming_dot, notificationBullet);
nav.setIcon(navMutate);

现在我遇到了最后一个方法nav.setIcon(navMutate)抛出 NullPointerException 的问题。

不是那个nav或navMutate为空，它在操作系统中更进一步，这是堆栈跟踪

我在这里使用这两个变量：

最后的LayerDrawable navMutate = (LayerDrawable) nav .getIcon().mutate();

navMutate .setDrawableByLayerId(R.id.ic_menu_upcoming_dot, notificationBullet);

不可能是因为其中任何一个都是空的，否则它会在那之前崩溃

java.lang.NullPointerException
    at android.graphics.drawable.LayerDrawable$LayerState.<init>(LayerDrawable.java:671)
    at android.graphics.drawable.LayerDrawable.createConstantState(LayerDrawable.java:107)
    at android.graphics.drawable.LayerDrawable.<init>(LayerDrawable.java:99)
    at android.graphics.drawable.LayerDrawable$LayerState.newDrawable(LayerDrawable.java:696)
    at android.support.design.internal.BottomNavigationItemView.setIcon(BottomNavigationItemView.java:224)
    at android.support.design.internal.BottomNavigationItemView.initialize(BottomNavigationItemView.java:100)
    at android.support.design.internal.BottomNavigationMenuView.updateMenuView(BottomNavigationMenuView.java:313)
    at android.support.design.internal.BottomNavigationPresenter.updateMenuView(BottomNavigationPresenter.java:64)
    at android.support.v7.view.menu.MenuBuilder.dispatchPresenterUpdate(MenuBuilder.java:291)
    at android.support.v7.view.menu.MenuBuilder.onItemsChanged(MenuBuilder.java:1051)
    at android.support.v7.view.menu.MenuItemImpl.setIcon(MenuItemImpl.java:505)
    at _redacted_.ui.NavActivity.setupBottomNav(NavActivity.java:424)
    at _redacted_.ui.NavActivity.onCreate(NavActivity.java:182)
    at android.app.Activity.performCreate(Activity.java:5231)
    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2159)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)
    at android.app.ActivityThread.access$800(ActivityThread.java:135)
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
    at android.os.Handler.dispatchMessage(Handler.java:102)
    at android.os.Looper.loop(Looper.java:136)
    at android.app.ActivityThread.main(ActivityThread.java:5017)
    at java.lang.reflect.Method.invokeNative(Native Method)
    at java.lang.reflect.Method.invoke(Method.java:515)
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
    at dalvik.system.NativeStart.main(Native Method)

它似乎只发生在低于 5 的 Android 版本上（所以 SDK 16-19）

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1 回答 1

0

您可以使用本机界面设置徽章（通知）图标和计数

只需添加材料组件依赖项

implementation 'com.google.android.material:material:1.1.0-alpha09'

并像这样使用它：

private fun updateUnreadedMessagesCountView(count: Int) {
        if (count == 0)
            bnv_bottom_navigation.removeBadge(R.id.messagesListFragment)
        else
            bnv_bottom_navigation.getOrCreateBadge(R.id.messagesListFragment).number = count
    }

R.id.messagesListFragment菜单项的 ID在哪里。在 SDK 19 上测试

于 2019-09-05T11:22:02.637 回答