Modal Bottom Sheet无法占满屏幕（含自定义偏移）的问题解决

想要实现Modal Bottom Sheet填满屏幕并扣除自定义偏移量的效果，已编写对应样式代码、重写BottomSheetDialogFragment的onCreateDialog方法及布局文件，但实际效果未达预期。通过布局检查器发现承载Bottom Sheet的FrameLayout仍处于wrap_content状态，需要找到无需使用findViewById（避免ID变更风险）的解决办法。

现有代码如下：

样式代码 #

<style name="Widget.App.HuddlePostBottomSheet" parent="ThemeOverlay.MaterialComponents.BottomSheetDialog">
    <item name="bottomSheetStyle">@style/Widget.App.HuddlePostBottomSheet.Modal</item>
</style>

<style name="Widget.App.HuddlePostBottomSheet.Modal" parent="Widget.MaterialComponents.BottomSheet.Modal">
    <item name="backgroundTint">@color/colorSurface</item>
    <item name="shapeAppearance">@style/ShapeAppearance.App.HuddlePostBottomSheet</item>
    <item name="behavior_fitToContents">false</item>
    <item name="behavior_skipCollapsed">false</item>
    <item name="behavior_draggable">true</item>
    <item name="behavior_expandedOffset">120dp</item>
    <item name="shouldRemoveExpandedCorners">false</item>
</style>

Fragment代码 #

class HuddlePostFragment : BottomSheetDialogFragment() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setStyle(STYLE_NORMAL,R.style.Widget_App_HuddlePostBottomSheet)
    }

    override fun onCreateDialog(savedInstanceState: Bundle?): Dialog {
        val dialog =  super.onCreateDialog(savedInstanceState)
        if (dialog is BottomSheetDialog) {
            dialog.behavior.apply {
                isFitToContents = false
                state = BottomSheetBehavior.STATE_EXPANDED
            }
        }
        return dialog
    }
}

布局文件 #

<layout 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">

    <androidx.constraintlayout.widget.ConstraintLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent">

        // UI goes here

    </androidx.constraintlayout.widget.ConstraintLayout>

</layout>

核心思路 #

不依赖固定ID，通过BottomSheetBehavior的特性识别承载容器，直接调整其布局高度为屏幕高度减去自定义偏移量，同时确保Behavior的配置生效。

修改后的Fragment代码 #

class HuddlePostFragment : BottomSheetDialogFragment() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setStyle(STYLE_NORMAL, R.style.Widget_App_HuddlePostBottomSheet)
    }

    override fun onCreateDialog(savedInstanceState: Bundle?): Dialog {
        val dialog = super.onCreateDialog(savedInstanceState) as BottomSheetDialog
        dialog.behavior.apply {
            isFitToContents = false
            // 从资源中读取偏移量，和样式保持一致
            expandedOffset = resources.getDimensionPixelSize(R.dimen.bottom_sheet_expanded_offset)
            state = BottomSheetBehavior.STATE_EXPANDED
        }
        return dialog
    }

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)
        
        // 遍历父View，找到带有BottomSheetBehavior的容器
        var currentView = view.parent as View
        var sheetBehavior: BottomSheetBehavior<*>? = null
        
        while (sheetBehavior == null && currentView.parent != null) {
            sheetBehavior = runCatching { BottomSheetBehavior.from(currentView) }.getOrNull()
            if (sheetBehavior == null) {
                currentView = currentView.parent as View
            }
        }

        sheetBehavior?.let { behavior ->
            // 计算容器高度：屏幕高度 - 偏移量
            val screenHeight = resources.displayMetrics.heightPixels
            currentView.layoutParams.height = screenHeight - behavior.expandedOffset
            // 强制刷新布局
            currentView.requestLayout()
        }
    }
}

补充说明 #

1. 确保在res/values/dimens.xml中定义偏移量，和样式中的120dp对应：

<dimen name="bottom_sheet_expanded_offset">120dp</dimen>

2. 该方案通过BottomSheetBehavior.from()方法识别容器，避免依赖官方内部ID，降低后续版本变更的风险；
3. 在onViewCreated中调整容器高度，确保View已经加载完成，布局参数修改能生效；
4. 保留样式中的配置，和代码中的设置形成互补，确保Behavior的状态和偏移量一致。

内容的提问来源于stack exchange，提问作者ShahiM