在 DrawerLayout 中以编程方式更改浮动操作按钮图像

Question

正如标题所示，当用户从 DrawerLayout 打开特定片段时，我试图以编程方式更改浮动图像按钮的 icon/image。这是我已经尝试过的：首先，这是 DrawerLayout class.

的 onCreate() 方法

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_menu_drawer);
    Toolbar toolbar = findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);

    FloatingActionButton fab = findViewById(R.id.fab);
    fab.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            Intent intent = new Intent(getApplicationContext(), TransaksiKeranjang.class);
            startActivity(intent);
        }
    });
    DrawerLayout drawer = findViewById(R.id.drawer_layout);
    NavigationView navigationView = findViewById(R.id.nav_view);
    NavController navController = Navigation.findNavController(this, R.id.nav_host_fragment);
    // Passing each menu ID as a set of Ids because each
    // menu should be considered as top level destinations.
    mAppBarConfiguration = new AppBarConfiguration.Builder(
            R.id.nav_transaksi, R.id.nav_pesanan, R.id.nav_sejarah, R.id.nav_inventory,
            R.id.nav_akun, R.id.nav_cabang, R.id.nav_laporan, R.id.nav_logout)
            .setDrawerLayout(drawer)
            .build();
    NavigationUI.setupActionBarWithNavController(this, navController, mAppBarConfiguration);
    NavigationUI.setupWithNavController(navigationView, navController);
    
    //Change fab icon when branch fragment open
    navController.addOnDestinationChangedListener(new NavController.OnDestinationChangedListener() {
        @Override
        public void onDestinationChanged(@NonNull NavController controller, @NonNull NavDestination destination, @Nullable Bundle arguments) {
            if (destination.getId() == R.id.nav_cabang) {
                fab.setImageDrawable(ContextCompat.getDrawable(getParent(), R.drawable.icon_add));
            }
        }
    });

    navigationView.getMenu().findItem(R.id.nav_logout).setOnMenuItemClickListener(menuItem -> {
        Intent intent = new Intent(MenuDrawer.this, Login.class);
        startActivity(intent);
        return true;
    });
}

然后这是存在浮动操作按钮的 xml :

<?xml version="1.0" encoding="utf-8"?>
<androidx.coordinatorlayout.widget.CoordinatorLayout 
 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"
 android:layout_width="match_parent"
 android:layout_height="match_parent"
 android:background="@drawable/background_fragment"
 tools:context=".MenuDrawer">

<com.google.android.material.appbar.AppBarLayout
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:theme="@style/Theme.HuwenakApp.AppBarOverlay">

    <androidx.appcompat.widget.Toolbar
        android:id="@+id/toolbar"
        android:layout_width="match_parent"
        android:layout_height="?attr/actionBarSize"
        android:background="@color/huwenak_brown"
        app:popupTheme="@style/Theme.HuwenakApp.PopupOverlay" />

</com.google.android.material.appbar.AppBarLayout>

<include layout="@layout/content_main" />

<com.google.android.material.floatingactionbutton.FloatingActionButton
    android:id="@+id/fab"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_gravity="bottom|end"
    android:layout_margin="@dimen/fab_margin"
    android:src="@drawable/icon_cart" />

</androidx.coordinatorlayout.widget.CoordinatorLayout>

问题是当我尝试更改 fab 图像时，我总是在这一行中收到 nullPointerException 错误：

fab.setImageDrawable(ContextCompat.getDrawable(getParent(), R.drawable.icon_add));

这很奇怪，因为 onClickListener 工作正常并且没有给我这个错误。

Answer 1

您必须添加上下文

fab.setImageDrawable(ContextCompat.getDrawable(this, R.drawable.icon_add))

您在文档中看到 getDrawable 需要上下文，如果您传递了父项，则会出现以下错误

尝试在空对象引用上调用虚方法'android.graphics.drawable.Drawable android.content.Context.getDrawable(int)'

getDrawable(@NonNull Context context, @DrawableRes int id)

在 DrawerLayout 中以编程方式更改浮动操作按钮图像

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