Android自定义控件阴影

top left right bottom分别是主体显示以外部分防止View设置过小对阴影切割

shadeX shadeY 为阴影偏移量向X,Y轴偏移，主体部分不会动阴影会根据X,Y移动。X>0向右移动,否则向左移动。Y>0向下移动，否则向上移动

solid_color设置主体部分颜色。stroke_color阴影部分颜色

shade_corner 绘制的drawable的圆角

shade_radius阴影部分的发散程度，越大越模糊

• 2.自定义Drawable代码

package com.kt.view.draw

import android.content.res.Resources
import android.graphics.Canvas
import android.graphics.Color
import android.graphics.ColorFilter
import android.graphics.Paint
import android.graphics.PixelFormat
import android.graphics.Rect
import android.graphics.RectF
import android.graphics.drawable.Drawable
import android.os.Build
import android.util.AttributeSet
import android.util.Log
import androidx.annotation.RequiresApi
import com.kt.view.R
import org.xmlpull.v1.XmlPullParser


class ShadeWidget(): Drawable() {


    private var paint: Paint? = null
    private var mRect: Rect? = null
    private var newPaint = Paint()
    private var shadeTop = 0
    private var shadeBottom = 0
    private var shadeRight = 0
    private var shadeLeft = 0
    private var shadeCorner = 0
    private var shadeRadius = 0
    private var shadeX = 0
    private var shadeY = 0
    private var solidColor = Color.TRANSPARENT
    private var strokeColor = Color.TRANSPARENT


    init {
        paint = Paint()
        mRect = Rect()
    }
    
    override fun inflate(
        r: Resources,
        parser: XmlPullParser,
        attrs: AttributeSet,
        theme: Resources.Theme?
    ) {
        super.inflate(r, parser, attrs, theme)
        val attributes = r.obtainAttributes(attrs, R.styleable.shade_widget)
        shadeTop = attributes.getDimensionPixelSize(R.styleable.shade_widget_top, 0)
        shadeLeft = attributes.getDimensionPixelSize(R.styleable.shade_widget_left, 0)
        shadeRight = attributes.getDimensionPixelSize(R.styleable.shade_widget_right, 0)
        shadeBottom = attributes.getDimensionPixelSize(R.styleable.shade_widget_bottom, 0)
        solidColor = attributes.getColor(R.styleable.shade_widget_solid_color, Color.TRANSPARENT)
        strokeColor = attributes.getColor(R.styleable.shade_widget_stroke_color, Color.BLACK)
        shadeX = attributes.getColor(R.styleable.shade_widget_shadeX, 0)
        shadeY = attributes.getColor(R.styleable.shade_widget_shadeY, 0)
        shadeCorner = attributes.getDimensionPixelSize(R.styleable.shade_widget_shade_corner,0)
        shadeRadius = attributes.getInt(R.styleable.shade_widget_shade_radius,0)
        attributes.recycle()
    }

    @RequiresApi(Build.VERSION_CODES.Q)
    override fun draw(canvas: Canvas) {
        newPaint.setColor(solidColor)
        mRect!!.set(bounds.left+shadeLeft, bounds.top+shadeTop, bounds.right-shadeRight, bounds.bottom-shadeBottom)
        newPaint.setShadowLayer(shadeRadius.toFloat(), 100F, 100F, strokeColor)
        canvas.drawRoundRect将Drawable绘制出来。
+ 3(RectF(mRect), shadeCorner.toFloat(), shadeCorner.toFloat(), newPaint)
    }



    override fun setAlpha(alpha: Int) {
        paint!!.alpha = alpha
    }

    override fun setColorFilter(colorFilter: ColorFilter?) {
        paint!!.setColorFilter(colorFilter)
    }

    override fun getOpacity(): Int {
        return PixelFormat.TRANSLUCENT
    }
}

上面代码核心为draw方法，在此处调用setShadowLayer设置阴影，最终由canvas.drawRoundRect将Drawable绘制出来。

<?xml version="1.0" encoding="utf-8"?>
<drawable class="com.kt.view.draw.ShadeWidget"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:android="http://schemas.android.com/apk/res/android"
    app:top="50dp"
    app:bottom="50dp"
    app:left="50dp"
    app:right="50dp"
    app:shade_corner="10dp"
    app:shade_radius="130"
    app:solid_color="#000000"
    app:stroke_color="#666666">
</drawable>