如果您正在使用材质组件主题，您可以通过将背景颜色设置为透明，然后将布局的背景设置为四舍五入来覆盖BottomSheetDialog的默认行为。

    <style name="Theme.MyApp" parent="Theme.MaterialComponents.DayNight.DarkActionBar">
        <!-- Customize your theme here. -->
        <item name="bottomSheetDialogTheme">@style/BottomSheetDialog</item>
    </style>

    <style name="BottomSheetDialog" parent="ThemeOverlay.MaterialComponents.BottomSheetDialog">
        <item name="bottomSheetStyle">@style/bottomSheetStyleWrapper</item>
    </style>

    <style name="bottomSheetStyleWrapper" parent="Widget.MaterialComponents.BottomSheet.Modal">
        <item name="android:backgroundTint">@android:color/transparent</item>
    </style>

rounded_corner.xml:

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android"
    android:shape="rectangle">
    <solid android:color="@color/white"/>
    <corners android:topLeftRadius="26dp"
        android:topRightRadius="26dp"/>

</shape>

然后将形状应用到你的底部表格根布局的背景:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@drawable/rounded_corner">

    <!-- 
       other layout components
     -->

</LinearLayout>

注意，如果你在底部表单布局中使用Webview这样的组件，你可能无法实现预期的圆角，因为Webview有一个默认的白色背景。在这种情况下，你可以像这样简单地删除背景:

webView.setBackgroundColor(0);

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>

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。

使用新的材质组件库，您可以使用样式中的shapeAppearanceOverlay属性自定义组件的形状(注意:它至少需要1.1.0版本)

只需使用BottomSheetDialogFragment覆盖onCreateView方法，然后为BottomSheet对话框定义自定义样式。

在你的应用主题的styles.xml中定义bottomSheetDialogTheme属性:

  <!-- Base application theme. -->
  <style name="AppTheme" parent="Theme.MaterialComponents.Light">
    <!-- Customize your theme here. -->
    <item name="colorPrimary">@color/colorPrimary</item>
    ....
    <item name="bottomSheetDialogTheme">@style/CustomBottomSheetDialog</item>
  </style>

然后用shapeAppearanceOverlay定义你最喜欢的形状

  <style name="CustomBottomSheetDialog" parent="@style/ThemeOverlay.MaterialComponents.BottomSheetDialog">
    <item name="bottomSheetStyle">@style/CustomBottomSheet</item>
  </style>

  <style name="CustomBottomSheet" parent="Widget.MaterialComponents.BottomSheet">
    <item name="shapeAppearanceOverlay">@style/CustomShapeAppearanceBottomSheetDialog</item>
  </style>

  <style name="CustomShapeAppearanceBottomSheetDialog" parent="">
    <item name="cornerFamily">rounded</item>
    <item name="cornerSizeTopRight">16dp</item>
    <item name="cornerSizeTopLeft">16dp</item>
    <item name="cornerSizeBottomRight">0dp</item>
    <item name="cornerSizeBottomLeft">0dp</item>
  </style>

你可以在你的BottomSheetDialogFragment中获得相同的行为覆盖这个方法(而不是在你的应用主题中添加bottomSheetDialogTheme):

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

在这种情况下，你只在一个BottomSheetDialogFragment中使用这个themeOverlay，而不是在所有的应用程序中。

关于EXPANDED STATE的重要注意事项:

在展开状态下，BottomSheet有平角。你可以在github repo查看官方评论:

我们的设计团队坚持认为圆角表示可滚动内容，而平角表示没有额外的内容。因此，他们不希望我们用fitToContents添加这个更改。

这个行为是由BottomSheetBehavior提供的，不可能重写它。 然而，有一个解决办法->免责声明:它可以停止工作在下一个版本!!

你可以在BottomSheetDialogFragment中添加一个BottomSheetCallback:

  @NonNull @Override public Dialog onCreateDialog(@Nullable Bundle savedInstanceState) {
    Dialog dialog = super.onCreateDialog(savedInstanceState);


    ((BottomSheetDialog)dialog).getBehavior().addBottomSheetCallback(new BottomSheetBehavior.BottomSheetCallback() {

      @Override public void onStateChanged(@NonNull View bottomSheet, int newState) {
        if (newState == BottomSheetBehavior.STATE_EXPANDED) {
          //In the EXPANDED STATE apply a new MaterialShapeDrawable with rounded cornes
          MaterialShapeDrawable newMaterialShapeDrawable = createMaterialShapeDrawable(bottomSheet);
          ViewCompat.setBackground(bottomSheet, newMaterialShapeDrawable);
        }
      }

      @Override public void onSlide(@NonNull View bottomSheet, float slideOffset) {

      }
    });

    return dialog;
  }

  @NotNull private MaterialShapeDrawable createMaterialShapeDrawable(@NonNull View bottomSheet) {
    ShapeAppearanceModel shapeAppearanceModel =

      //Create a ShapeAppearanceModel with the same shapeAppearanceOverlay used in the style
      ShapeAppearanceModel.builder(getContext(), 0, R.style.CustomShapeAppearanceBottomSheetDialog)
        .build();

      //Create a new MaterialShapeDrawable (you can't use the original MaterialShapeDrawable in the BottoSheet)
      MaterialShapeDrawable currentMaterialShapeDrawable = (MaterialShapeDrawable) bottomSheet.getBackground();
      MaterialShapeDrawable newMaterialShapeDrawable = new MaterialShapeDrawable((shapeAppearanceModel));
      //Copy the attributes in the new MaterialShapeDrawable
      newMaterialShapeDrawable.initializeElevationOverlay(getContext());
      newMaterialShapeDrawable.setFillColor(currentMaterialShapeDrawable.getFillColor());
      newMaterialShapeDrawable.setTintList(currentMaterialShapeDrawable.getTintList());
      newMaterialShapeDrawable.setElevation(currentMaterialShapeDrawable.getElevation());
      newMaterialShapeDrawable.setStrokeWidth(currentMaterialShapeDrawable.getStrokeWidth());
      newMaterialShapeDrawable.setStrokeColor(currentMaterialShapeDrawable.getStrokeColor());
      return newMaterialShapeDrawable;
  }

在STATE_EXPANDED上禁用圆角平化的短解决方案:

@SuppressLint("RestrictedApi")
override fun onCreateDialog(savedInstanceState: Bundle?): Dialog {
    val dialog = super.onCreateDialog(savedInstanceState)
    
    //Disable animator that flats the rounded corners
    (dialog as BottomSheetDialog).behavior.disableShapeAnimations()

    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)
            }
        }
}