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
}

创建一个自定义的圆角绘图，并将其设置为你的BottomSheetDialogFragment的布局根的背景

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

<solid android:color="@color/colorPrimary" />

<corners
    android:bottomLeftRadius="0dp"
    android:bottomRightRadius="0dp"
    android:topLeftRadius="12dp"
    android:topRightRadius="12dp" />

</shape>

然后简单地将下面的代码添加到您的BottomSheetDialogFragment类

@Override
public void setupDialog(Dialog dialog, int style) {
    super.setupDialog(dialog, style);
    View contentView = View.inflate(getContext(), 
R.layout.fragment_bottom_sheet, null);
    dialog.setContentView(contentView);

    CoordinatorLayout.LayoutParams params = (CoordinatorLayout.LayoutParams) ((View) contentView.getParent())
            .getLayoutParams();
    CoordinatorLayout.Behavior behavior = params.getBehavior();
    ((View) contentView.getParent()).setBackgroundColor(ContextCompat.getColor(getContext(), android.R.color.transparent));
}

你甚至可以像下面这样使用参数来设置边距

params.setMargins(50, 0, 50, 0);

正如在其他答案中指出的，当state为BottomSheetBehavior时。STATE_EXPANDED角将被压平。

你可以通过设置BottomSheetBehavior的peekHeight属性并使用自定义样式来克服这个问题。

abstract class BaseBottomSheetFragment : BottomSheetDialogFragment(){

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
    
        if (state == BottomSheetBehavior.STATE_EXPANDED) {
            val displayMetrics = DisplayMetrics()
            requireActivity().windowManager!!.defaultDisplay!!.getMetrics(displayMetrics)
            (dialog as BottomSheetDialog).behavior.peekHeight = displayMetrics.heightPixels
        } else {
            (dialog as BottomSheetDialog).behavior.state = state
        }
    }

    override fun getTheme(): Int {
        return R.style.CustomBottomSheetDialog
    }
}

CustomBottomSheetDialog风格

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

<style name="CustomMaterialButtonStyle" parent="@style/Widget.MaterialComponents.Button">
    <item name="cornerRadius">@dimen/dialog_bottom_radius</item>
</style>

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

<style name="CustomShapeAppearanceBottomSheetDialog" parent="">
    <item name="android:background">@android:color/transparent</item>
    <item name="backgroundTint">@android:color/transparent</item>
    <item name="cornerFamily">rounded</item>
    <item name="cornerSizeTopRight">@dimen/dialog_bottom_radius</item>
    <item name="cornerSizeTopLeft">@dimen/dialog_bottom_radius</item>
    <item name="cornerSizeBottomRight">0dp</item>
    <item name="cornerSizeBottomLeft">0dp</item>
</style>

我今天也检查了同样的事情，是的，你是对的，下面的代码

this.getDialog().getWindow().setBackgroundDrawableResource(R.drawable.charge_layout_background);

这适用于片段背景，所以相反，你应该从对话框窗口获得底部表视图，并改变背景，这里是代码

 @SuppressLint("RestrictedApi")
    @Override
    public void setupDialog(Dialog dialog, int style) {
        super.setupDialog(dialog, style);
        View rootView = getActivity().getLayoutInflater().inflate(R.layout.view_member_info,null,false);
        unbinder = ButterKnife.bind(this, rootView);
        adjustUIComponents();
        dialog.setContentView(rootView);
        FrameLayout bottomSheet = (FrameLayout) dialog.getWindow().findViewById(android.support.design.R.id.design_bottom_sheet);
        bottomSheet.setBackgroundResource(R.drawable.container_background);
    }

这里的底部是你想要改变的实际视图。

如果你需要setFitContents=true，我尝试了通过钩子onStateChanged解决方案，但一旦对话框达到扩展状态，它就会从直角闪烁到圆角。这很烦人。

有一种替代的解决方案，它不会导致闪烁，不需要使用私有api，而且更易于阅读(恕我冒犯)。

查看BottomSheetBehavior的代码，我们发现:

  /** True if Behavior has a non-null value for the @shapeAppearance attribute */
  private boolean shapeThemingEnabled;

事实证明，如果形状主题被禁用，MaterialShapeDrawable将不会被使用。我们在BottomSheetBehavior.onLayout()中找到了这个:

// Only set MaterialShapeDrawable as background if shapeTheming is enabled, otherwise will
// default to android:background declared in styles or layout.
if (shapeThemingEnabled && materialShapeDrawable != null) {
  ViewCompat.setBackground(child, materialShapeDrawable);
}

默认为android:background正是我们所需要的，因为这意味着完全控制如何渲染背景。

我们可以通过创建一个单独的样式来禁用材质主题，并将shapeAppearance和shapeAppearance overlay设置为null:

<style name="Theme.YourApp.NoShapeBottomSheetDialog" parent="Theme.MaterialComponents.BottomSheetDialog">
  <item name="bottomSheetStyle">@style/Theme.YourApp.NoShapeButtonSheet</item>
</style>

<style name="Theme.YourApp.NoShapeButtonSheet" parent="Widget.MaterialComponents.BottomSheet.Modal">
  <item name="shapeAppearance">@null</item>
  <item name="shapeAppearanceOverlay">@null</item>
</style>

扩展BottomSheetDialogFragment和覆盖onCreateDialog:

public Dialog onCreateDialog(@Nullable Bundle savedInstanceState) {
  return new BottomSheetDialog(requireContext(),
                R.style.Theme_Grupin_NoShapeBottomSheetDialog);
}

下面的表格现在是裸露的，没有任何背景。所以我们可以添加任何我们想要的背景，没有动画将被触发。

简单的解决方案:

class TopRoundedCornersFragment : BottomSheetDialogFragment() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)

        setStyle(STYLE_NORMAL, R.style.AppBottomSheetDialogTheme)
    }
}

在styles.xml

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

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

最后，创建一个顶部圆角可绘制资源(bottom_sheet_dialog_bg.xml)

<shape xmlns:android="http://schemas.android.com/apk/res/android"
    android:shape="rectangle">

    <solid android:color="@android:color/white" />
    <corners
        android:topLeftRadius="4dp"
        android:topRightRadius="4dp" />

</shape>