/**
 * @Description: 類作用描述
 * @Author: hukui
 * @Date: 2020/9/7 17:20
 */

import android.annotation.TargetApi;
import android.content.Context;
import android.content.res.TypedArray;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.RectF;
import android.os.Build;
import android.util.AttributeSet;
import android.view.View;
import android.view.ViewGroup;

import androidx.annotation.Nullable;

import com.mylibrary.api.R;


/**
 * 嘗試一個(gè)自定義陰影View
 */
public class ShadeViewGroup extends ViewGroup {
    private float deltaLength;
    private float cornerRadius;
    private Paint mShadowPaint;
    private boolean drawShadow;
    private Context mContext;
    private int shadowColor;
    private float shadowRadius;
    private float dx;
    private float dy;

    public ShadeViewGroup(Context context) {
        this(context, null);
    }

    public ShadeViewGroup(Context context, @Nullable AttributeSet attrs) {
        this(context, attrs, 0);
    }

    public ShadeViewGroup(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        mContext = context;
        initView(attrs);
    }

    @Override
    protected void onLayout(boolean changed, int l, int t, int r, int b) {
        View child = getChildAt(0);
        int measuredWidth = getMeasuredWidth();
        int measuredHeight = getMeasuredHeight();
        int childMeasureWidth = child.getMeasuredWidth();
        int childMeasureHeight = child.getMeasuredHeight();
        child.layout((measuredWidth - childMeasureWidth) / 2, (measuredHeight - childMeasureHeight) / 2, (measuredWidth + childMeasureWidth) / 2, (measuredHeight + childMeasureHeight) / 2);
    }


    /**
     * 初始化信息變量
     */
    private void initView(AttributeSet attrs) {
        TypedArray a = mContext.obtainStyledAttributes(attrs, R.styleable.ShadeViewGroup);
        shadowColor = a.getColor(R.styleable.ShadeViewGroup_containerShadowColor, Color.WHITE);
        shadowRadius = a.getDimension(R.styleable.ShadeViewGroup_containerShadowRadius, 0);
        dx = a.getDimension(R.styleable.ShadeViewGroup_deltaX, 0);
        dy = a.getDimension(R.styleable.ShadeViewGroup_deltaY, 0);
        deltaLength = a.getDimension(R.styleable.ShadeViewGroup_containerDeltaLength, 0);
        cornerRadius = a.getDimension(R.styleable.ShadeViewGroup_containerCornerRadius, 0);

        drawShadow = a.getBoolean(R.styleable.ShadeViewGroup_enable, true);
        a.recycle();
        initShadowPaint();
    }

    public void setShadowColor(int shadowColor) {
        this.shadowColor = shadowColor;
        initShadowPaint();
        invalidate();
    }

    private void initShadowPaint() {
        mShadowPaint = new Paint();
        mShadowPaint.setStyle(Paint.Style.FILL);
        mShadowPaint.setAntiAlias(true);
        mShadowPaint.setColor(shadowColor);
        mShadowPaint.setShadowLayer(shadowRadius, dx, dy, shadowColor);
    }


    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
        if (getChildCount() != 1) {
            throw new IllegalStateException("子View只能有一個(gè)");
        }
        int measuredWidth = getMeasuredWidth();
        int measuredHeight = getMeasuredHeight();
        int widthMode = MeasureSpec.getMode(widthMeasureSpec);
        int heightMode = MeasureSpec.getMode(heightMeasureSpec);
        View child = getChildAt(0);
        LayoutParams layoutParams = (LayoutParams) child.getLayoutParams();
        int childBottomMargin = (int) (Math.max(deltaLength, layoutParams.bottomMargin) + 1);
        int childLeftMargin = (int) (Math.max(deltaLength, layoutParams.leftMargin) + 1);
        int childRightMargin = (int) (Math.max(deltaLength, layoutParams.rightMargin) + 1);
        int childTopMargin = (int) (Math.max(deltaLength, layoutParams.topMargin) + 1);
        int widthMeasureSpecMode;
        int widthMeasureSpecSize;
        int heightMeasureSpecMode;
        int heightMeasureSpecSize;
        if (widthMode == MeasureSpec.UNSPECIFIED) {
            widthMeasureSpecMode = MeasureSpec.UNSPECIFIED;
            widthMeasureSpecSize = MeasureSpec.getSize(widthMeasureSpec);
        } else {
            if (layoutParams.width == LayoutParams.MATCH_PARENT) {
                widthMeasureSpecMode = MeasureSpec.EXACTLY;
                widthMeasureSpecSize = measuredWidth - childLeftMargin - childRightMargin;
            } else if (LayoutParams.WRAP_CONTENT == layoutParams.width) {
                widthMeasureSpecMode = MeasureSpec.AT_MOST;
                widthMeasureSpecSize = measuredWidth - childLeftMargin - childRightMargin;
            } else {
                widthMeasureSpecMode = MeasureSpec.EXACTLY;
                widthMeasureSpecSize = layoutParams.width;
            }
        }
        if (heightMode == MeasureSpec.UNSPECIFIED) {
            heightMeasureSpecMode = MeasureSpec.UNSPECIFIED;
            heightMeasureSpecSize = MeasureSpec.getSize(heightMeasureSpec);
        } else {
            if (layoutParams.height == LayoutParams.MATCH_PARENT) {
                heightMeasureSpecMode = MeasureSpec.EXACTLY;
                heightMeasureSpecSize = measuredHeight - childBottomMargin - childTopMargin;
            } else if (LayoutParams.WRAP_CONTENT == layoutParams.height) {
                heightMeasureSpecMode = MeasureSpec.AT_MOST;
                heightMeasureSpecSize = measuredHeight - childBottomMargin - childTopMargin;
            } else {
                heightMeasureSpecMode = MeasureSpec.EXACTLY;
                heightMeasureSpecSize = layoutParams.height;
            }
        }
        measureChild(child, MeasureSpec.makeMeasureSpec(widthMeasureSpecSize, widthMeasureSpecMode), MeasureSpec.makeMeasureSpec(heightMeasureSpecSize, heightMeasureSpecMode));
        int parentWidthMeasureSpec = MeasureSpec.getMode(widthMeasureSpec);
        int parentHeightMeasureSpec = MeasureSpec.getMode(heightMeasureSpec);
        int height = measuredHeight;
        int width = measuredWidth;
        int childHeight = child.getMeasuredHeight();
        int childWidth = child.getMeasuredWidth();
        if (parentHeightMeasureSpec == MeasureSpec.AT_MOST) {
            height = childHeight + childTopMargin + childBottomMargin;
        }
        if (parentWidthMeasureSpec == MeasureSpec.AT_MOST) {
            width = childWidth + childRightMargin + childLeftMargin;
        }
        if (width < childWidth + 2 * deltaLength) {
            width = (int) (childWidth + 2 * deltaLength);
        }
        if (height < childHeight + 2 * deltaLength) {
            height = (int) (childHeight + 2 * deltaLength);
        }
        if (height != measuredHeight || width != measuredWidth) {
            setMeasuredDimension(width, height);
        }
    }

    static class LayoutParams extends MarginLayoutParams {

        public LayoutParams(Context c, AttributeSet attrs) {
            super(c, attrs);
        }

        public LayoutParams(int width, int height) {
            super(width, height);
        }

        public LayoutParams(MarginLayoutParams source) {
            super(source);
        }

        public LayoutParams(ViewGroup.LayoutParams source) {
            super(source);
        }
    }

    @Override
    protected ViewGroup.LayoutParams generateDefaultLayoutParams() {
        return new LayoutParams(LayoutParams.WRAP_CONTENT, LayoutParams.WRAP_CONTENT);
    }

    @Override
    protected ViewGroup.LayoutParams generateLayoutParams(ViewGroup.LayoutParams p) {
        return new LayoutParams(p);
    }

    @Override
    public ViewGroup.LayoutParams generateLayoutParams(AttributeSet attrs) {
        return new LayoutParams(getContext(), attrs);
    }

    @TargetApi(Build.VERSION_CODES.LOLLIPOP)
    @Override
    protected void dispatchDraw(Canvas canvas) {
        if (drawShadow) {
            if (getLayerType() != LAYER_TYPE_SOFTWARE) {
                setLayerType(LAYER_TYPE_SOFTWARE, null);
            }
            View child = getChildAt(0);
            int left = child.getLeft();
            int top = child.getTop();
            int right = child.getRight();
            int bottom = child.getBottom();
            RectF rectF = new RectF(left, top, right, bottom);
            canvas.drawRoundRect(rectF, cornerRadius, cornerRadius, mShadowPaint);
        }
        super.dispatchDraw(canvas);
    }
}

    <declare-styleable name="ShadeViewGroup">
        <attr name="containerShadowColor" format="color" />
        <attr name="containerShadowRadius" format="dimension" />
        <attr name="containerDeltaLength" format="dimension" />
        <attr name="containerCornerRadius" format="dimension" />
        <attr name="deltaX" format="dimension" />
        <attr name="deltaY" format="dimension" />
        <attr name="enable" format="boolean" />
    </declare-styleable>

簡單用法

      <com.mylibrary.api.widget.ShadeViewGroup
                android:id="@+id/shopCar_EditLayout"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:layout_gravity="bottom"
                android:layout_marginStart="-6dp"
                android:layout_marginEnd="-6dp"
                android:layout_marginBottom="-6dp"
                android:visibility="gone"
                app:containerCornerRadius="@dimen/radius2"
                app:containerDeltaLength="@dimen/shardRadius"
                app:containerShadowColor="@color/shadowColor"
                app:containerShadowRadius="@dimen/shardRadius"></com.mylibrary.api.widget.ShadeViewGroup>