详解Android如何实现阴影效果

<Androidx.appcompat.widget.LinearLayoutCompat
    android:layout_margin="15dp"
    android:layout_width="match_parent"
    android:layout_height="100dp"
    android:background="@android:color/holo_blue_bright"
    android:elevation="10dp"
    android:translationZ="10dp"
    android:paddingBottom="10dp"
    />

<androidx.cardview.widget.CardView
    android:layout_margin="15dp"
    android:layout_width="match_parent"
    android:layout_height="100dp"
    android:outlineAmbientShadowColor="@android:color/holo_blue_bright"
    android:outlineSpotShadowColor="@android:color/holo_red_dark"
    app:cardElevation="5dp"
    app:cardMaxElevation="10dp"
    />

<TextView
android:id="@+id/test_shadow"
android:layout_gravity="center"
android:layout_height="wrap_content"
android:layout_width="wrap_content"
android:shadowColor="#aa22ff22"
android:shadowDx="0"
android:shadowDy="0"
android:shadowRadius="10"
android:text="Test Shadow"
android:textColor="#cc000000"
android:textSize="60sp" />

<?xml version="1.0" encoding="utf-8"?>
<layer-list xmlns:android="Http://schemas.android.com/apk/res/android">
    <!-- 阴影图片，android:left表示阴影图片左边到背景图片左边的距离
    android:top表示阴影图片上边到背景图片上边的距离-->
    <item android:left="5dp"
        android:top="5dp">
        <shape>
            <solid android:color="#60000000"/>
        </shape>
    </item>
    <!-- 背景图片，android:right表示阴影图片右边到背景图片右边的距离
    android:bottom表示阴影图片下边到背景图片下边的距离-->
    <item android:bottom="5dp"
        android:right="5dp">
        <shape>
            <solid android:color="#000000"/>
        </shape>
    </item>
</layer-list>

@Override
public void draw(@NonNull canvas canvas) {
    if (mBGColor != null) {
        if (mBgColor.length == 1) {
            mBgPaint.setColor(mBgColor[0]);
        } else {
            mBgPaint.setShader(new LinearGradient(mRect.left, mRect.height() / 2, mRect.right,
                    mRect.height() / 2, mBgColor, null, Shader.TileMode.CLAMP));
        }
    }

    if (mShape == SHAPE_ROUND) {
        canvas.drawRoundRect(mRect, mShapeRadius, mShapeRadius, mShadowPaint);
        canvas.drawRoundRect(mRect, mShapeRadius, mShapeRadius, mBgPaint);
    } else {
        canvas.drawCircle(mRect.centerX(), mRect.centerY(), Math.min(mRect.width(), mRect.height())/ 2, mShadowPaint);
        canvas.drawCircle(mRect.centerX(), mRect.centerY(), Math.min(mRect.width(), mRect.height())/ 2, mBgPaint);
    }
}