首先，你应该创建一个可绘制的XML文件，其中包含一个顶部圆角的形状，任何你想要的名称。 我将其命名为bottom rounded_top_shape.xml

<shape
xmlns:android="http://schemas.android.com/apk/res/android"
android:shape="rectangle"
>
<solid android:color="@android:color/white" />
<corners
    android:topLeftRadius="16dp"
    android:topRightRadius="16dp"
    />

然后在style.xml中添加这个

<style name="AppBottomSheetDialogTheme" parent="Theme.MaterialComponents.Light.BottomSheetDialog">
    <item name="bottomSheetStyle">@style/AppModalStyle</item>
</style>

<style name="AppModalStyle" parent="Widget.Design.BottomSheet.Modal">
    <item name="android:background">@drawable/rounded_top_shape</item>
</style>

然后在你的应用主题中添加如下所示的行

 <style name="MyAppTheme" parent="Theme.MaterialComponents.Light.Bridge">
    <!-- this line -->
    <item name="bottomSheetDialogTheme">@style/AppBottomSheetDialogTheme</item>
</style>

最简单和最干净的解决方案，对我来说，是把以下4行放在我的片段类的onViewCreated(View View, Bundle savedInstanceState)方法中:

@Override
public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
    View bottomSheet = (View) view.getParent();
    bottomSheet.setBackgroundTintMode(PorterDuff.Mode.CLEAR);
    bottomSheet.setBackgroundTintList(ColorStateList.valueOf(Color.TRANSPARENT));
    bottomSheet.setBackgroundColor(Color.TRANSPARENT);
}

这将允许您的自定义绘制圆角，以正确显示一旦设置为您的片段布局的顶层视图的背景。

本质上，这将覆盖默认的BottomSheetFragment属性关于颜色，tintMode和tintList。

使用它，就不需要打乱样式资源。

步骤1:

创建一个命名为rounded_background.xml的res/drawable:

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android"
  android:shape="rectangle">
  <corners
    android:topLeftRadius="32dp"
    android:topRightRadius="32dp" />
  <solid android:color="#D81B60" />
</shape>

步骤2:

创建这个样式来删除对话框背景:

<style name="NoBackgroundDialogTheme" parent="Theme.AppCompat.Light.Dialog">
    <item name="android:windowBackground">@null</item>
</style>

步骤3:

使用setBackgroundResource()将可绘制对象设置为对话框的根视图，并通过覆盖getTheme()方法设置样式

Java:

public class MyDialogFragment extends BottomSheetDialogFragment {

    @Override
    public int getTheme() {
        return R.style.NoBackgroundDialogTheme;
    }

    @Nullable
    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {

        View view = View.inflate(requireContext(), R.layout.bottom_sheet_profile, null);
        view.setBackgroundResource(R.drawable.rounded_background);
        return view;

    }
}

科特林：

class MyDialogFragment : BottomSheetDialogFragment() {

    override fun getTheme() = R.style.NoBackgroundDialogTheme

    override fun onCreateView(
        inflater: LayoutInflater,
        container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View {

        val view: View = View.inflate(requireContext(), R.layout.bottom_sheet_profile, null)
        view.setBackgroundResource(R.drawable.rounded_background)
        return view
    }

}

结果:

如果(view.setBackgroundResource(R.drawable.rounded_background))这一行不能工作，然后尝试设置片段的Xml格式的背景。

Koma Yip回答的另一个问题对我有用，你应该试试。

在drawable中创建一个xml，比如dialog_bg.xml <？XML版本="1.0"编码="utf-8"?> <形状xmlns: android = " http://schemas.android.com/apk/res/android " > <固体android:颜色= " @color /白色" / > <corners android:半径="30dp" /> <填充 android:左= " 10 dp” android:顶级= " 10 dp” android:对= " 10 dp” android:底部= " 10 dp " / > < / >形状

把这个放在你的布局XML根节点中:

将其设置为布局XML中的背景 android:背景= " @drawable / dialog_bg”

在onCreateView()中放入:

将对话框的背景设置为透明 dialog.getWindow()。setBackgroundDrawable(新ColorDrawable (Color.TRANSPARENT));

你必须改变底部的主题，以实现顶部圆形布局

创建一个自定义绘制background_bottom_sheet_dialog_fragment.xml:

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android"
   android:shape="rectangle">
    <corners
       android:topLeftRadius="8dp"
        android:topRightRadius="8dp" />
    <padding android:top="0dp" />
    <solid android:color="@color/white" />
</shape>

然后在styles.xml上使用drawable作为背景覆盖bottomSheetDialogTheme:

<!--Bottom sheet-->
<style name="BottomSheet" parent="@style/Widget.Design.BottomSheet.Modal">
    <item 
    name="android:background">@drawable/background_bottom_sheet_dialog_fragment
    </item>
</style>

<style name="BaseBottomSheetDialog" 
    parent="@style/Theme.Design.Light.BottomSheetDialog">
    <item name="android:windowIsFloating">false</item>
    <item name="bottomSheetStyle">@style/BottomSheet</item>
</style>

<style name="BottomSheetDialogTheme" parent="BaseBottomSheetDialog" />

这将改变你的底页的背景布局

BottomSheetDialog

class SheetFragment() : BottomSheetDialogFragment() {

    lateinit var binding: SheetFragmentBinding;

  override fun onCreateDialog(savedInstanceState: Bundle?): Dialog {
    val dialog = super.onCreateDialog(savedInstanceState) as BottomSheetDialog;
    val view = View.inflate(context, R.layout.fragment_bottom_sheet, null);

    binding = DataBindingUtil.bind(view)!!;
    binding.viewModel = SheetFragmentVM();

    dialog.setContentView(view);

    var bottomSheetBehavior = BottomSheetBehavior.from(view.parent as View);
    bottomSheetBehavior.setPeekHeight(BottomSheetBehavior.PEEK_HEIGHT_AUTO);

    bottomSheetBehavior.setBottomSheetCallback(object : 
     BottomSheetBehavior.BottomSheetCallback() {
        override fun onStateChanged(bottomSheet: View, newState: Int) {
            if (BottomSheetBehavior.STATE_EXPANDED == newState) {
               // do on STATE_EXPANDED
            }
            if (BottomSheetBehavior.STATE_COLLAPSED == newState) {
                // do on STATE_COLLAPSED
            }

            if (BottomSheetBehavior.STATE_HIDDEN == newState) {
                dismiss()

            }
        }

        override fun onSlide(bottomSheet: View, slideOffset: Float) {
           // do on slide
        }
    })

    return dialog
}

我找到了一个简单的解决办法。 使用com.google.android.material:material:1.6.1

class MyBottomSheet: BottomSheetDialogFragment() {
    
      override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
            super.onViewCreated(view, savedInstanceState)
            disableShapeAnimation()
        }
    
      @SuppressLint("RestrictedApi", "VisibleForTests")
      private fun disableShapeAnimation() {
            try {
                val dlg = dialog as BottomSheetDialog
                dlg.behavior.disableShapeAnimations()
            } catch (ex: Exception) {
                Log.e("BaseBottomSheet", "disableShapeAnimation Exception:", ex)
            }
        }
}