在Android开发中我们会在设计稿中看到各种阴影效果，我们知道CardView可以添加阴影效果，不过可能并不是我们设计稿想要的效果，那我们如何可以更加灵活地给我们原生控件添加阴影效果，这就是下面所要描述的，当然也可以让设计师给个阴影切图，我们做下.9处理然后使用切图实现阴影效果。
下面看看如何用代码更灵活地去为原生控件实现阴影效果，源码可以查看 XSelector GitHub， 结尾也会贴出ShadowHelper源码。
先看效果图：
shadow.png
如果使用XSelector工具库引入对应的库implementation 'com.android.util:xselector:1.0.2'，使用方法如下，也可以直接使用该ShadowHelper 类去完成阴影效果。
XSelector.shadowHelper().setShape(ShadowHelper.SHAPE_CIRCLE)
.setBgColor(Color.parseColor("#FF3D00"))
.setShapeRadius(dpToPx(6))
.setShadowColor(Color.parseColor("#991DE9B6"))
.setShadowRadius(dpToPx(6))
.setOffsetX(dpToPx(4))
.setOffsetY(dpToPx(4))
.into(textView5);
使用方法存在但不限于上述使用方法，具体详细方法如下：
| 模块 | 方法名 | 描述 |
|---|---|---|
| ShadowHelper | setShape | 设置背景形状，椭圆或者圆形 |
| setBgColor | 背景颜色 | |
| setShapeRadius | 设置背景半径 | |
| setShadeSide | 设置阴影方向，默认四周 | |
| setShadeRadius | 设置阴影半径 | |
| setShadowColor | 设置阴影颜色 | |
| setOffsetX | 设置阴影X轴偏移量 | |
| setOffsetY | 设置阴影Y轴偏移量 | |
| setShadowAlpha | 设置阴影透明度 | |
| into | 目标View |
ShadowHelper 源码如下：
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.ColorFilter;
import android.graphics.LinearGradient;
import android.graphics.Paint;
import android.graphics.PixelFormat;
import android.graphics.PorterDuff;
import android.graphics.PorterDuffXfermode;
import android.graphics.Rect;
import android.graphics.RectF;
import android.graphics.Shader;
import android.graphics.drawable.Drawable;
import android.support.annotation.IntRange;
import android.support.annotation.NonNull;
import android.support.annotation.Nullable;
import android.support.v4.view.ViewCompat;
import android.view.View;
/**
* 类名称：ShadowHelper
* 创建者：Create by liujc
* 创建时间：Create on 2018/5/28
* 描述：控件阴影效果
*/
public class ShadowHelper extends Drawable {
static ShadowHelper shadowHelper;
private Paint mPaint;
/**
* 阴影模糊半径，越大越模糊
*/
private int mShadowRadius;
/**
* 阴影颜色
*/
private int mShadowColor;
/**
* 背景形状
*/
private int mShape;
/**
* 背景圆角半径
*/
private int mShapeRadius;
/**
* 阴影x偏移(右偏移)
*/
private int mOffsetX;
/**
* 阴影y偏移(下偏移)
*/
private int mOffsetY;
/**
* 背景颜色
*/
private int mBgColor[];
private RectF mRect;
public final static int SHAPE_ROUND = 1;
public final static int SHAPE_CIRCLE = 2;
public static final int ALL = 0x1111;
public static final int LEFT = 0x0001;
public static final int TOP = 0x0010;
public static final int RIGHT = 0x0100;
public static final int BOTTOM = 0x1000;
/**
* 阴影边 例：0x1100 表示RIGHT和BOTTOM
*/
private int shadowSide = ALL;
private ShadowHelper(){
mShape = ShadowHelper.SHAPE_ROUND;
mShapeRadius = 0;
mShadowColor = Color.parseColor("#4d000000");
mShadowRadius = 18;
mOffsetX = 0;
mOffsetY = 0;
mBgColor = new int[1];
mBgColor[0] = Color.TRANSPARENT;
mPaint = new Paint();
mPaint.setColor(Color.TRANSPARENT);
mPaint.setAntiAlias(true);
mPaint.setShadowLayer(mShadowRadius, mOffsetX, mOffsetY, mShadowColor);
mPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.DST_ATOP));
}
public static ShadowHelper getInstance() {
shadowHelper = new ShadowHelper();
return shadowHelper;
}
public ShadowHelper setShape(int mShape) {
this.mShape = mShape;
return this;
}
public ShadowHelper setShadowSide(int shadowSide) {
this.shadowSide = shadowSide;
return this;
}
public ShadowHelper setShapeRadius(int ShapeRadius) {
this.mShapeRadius = ShapeRadius;
return this;
}
/**
* 设置阴影颜色
* @param shadowColor 例：R.color.colorPrimary
* @return
*/
public ShadowHelper setShadowColor(int shadowColor) {
this.mShadowColor = shadowColor;
mPaint.setShadowLayer(mShadowRadius, mOffsetX, mOffsetY, mShadowColor);
return this;
}
/**
* 设置阴影颜色
* @param shadowColor 例：#ffffff
* @return
*/
public ShadowHelper setShadowColor(String shadowColor) {
this.mShadowColor = Color.parseColor(shadowColor);
mPaint.setShadowLayer(mShadowRadius, mOffsetX, mOffsetY, mShadowColor);
return this;
}
public ShadowHelper setShadowRadius(int shadowRadius) {
this.mShadowRadius = shadowRadius;
mPaint.setShadowLayer(mShadowRadius, mOffsetX, mOffsetY, mShadowColor);
return this;
}
public ShadowHelper setOffsetX(int OffsetX) {
this.mOffsetX = OffsetX;
mPaint.setShadowLayer(mShadowRadius, mOffsetX, mOffsetY, mShadowColor);
return this;
}
public ShadowHelper setOffsetY(int OffsetY) {
this.mOffsetY = OffsetY;
mPaint.setShadowLayer(mShadowRadius, mOffsetX, mOffsetY, mShadowColor);
return this;
}
/**
* 设置背景颜色
* @param BgColor 例：R.color.colorPrimary
* @return
*/
public ShadowHelper setBgColor(int BgColor) {
this.mBgColor[0] = BgColor;
return this;
}
/**
* 设置背景颜色
* @param bgColor 例：#ffffff
* @return
*/
public ShadowHelper setBgColor(String bgColor) {
this.mBgColor[0] = Color.parseColor(bgColor);
return this;
}
public ShadowHelper setBgColor(int[] BgColor) {
this.mBgColor = BgColor;
return this;
}
public ShadowHelper setBgColor(String[] bgColor) {
int length = bgColor.length;
int[] color = new int[length];
for(int i=0;i < length;i++){
color[i] = Color.parseColor(bgColor[i]);
}
this.mBgColor = color;
return this;
}
public ShadowHelper setShadowAlpha(int i) {
setAlpha(i);
return this;
}
@Override
protected void onBoundsChange(Rect bounds) {
super.onBoundsChange(bounds);
int leftShadow = (shadowSide & LEFT) == LEFT ? mShadowRadius - mOffsetX : -mShapeRadius;
int topShadow = (shadowSide & TOP) == TOP ? mShadowRadius - mOffsetY : -mShapeRadius;
int rightShadow = (shadowSide & RIGHT) == RIGHT ? mShadowRadius + mOffsetX : -mShapeRadius;
int bottomShadow = (shadowSide & BOTTOM) == BOTTOM ? mShadowRadius + mOffsetY : -mShapeRadius;
mRect = new RectF(bounds.left + leftShadow, bounds.top + topShadow, bounds.right - rightShadow,
bounds.bottom - bottomShadow);
}
@Override
public void draw(@NonNull Canvas canvas) {
Paint newPaint = new Paint();
if (mBgColor != null) {
if (mBgColor.length == 1) {
newPaint.setColor(mBgColor[0]);
} else {
newPaint.setShader(new LinearGradient(mRect.left, mRect.height() / 2, mRect.right, mRect.height() / 2, mBgColor,
null, Shader.TileMode.CLAMP));
}
}
newPaint.setAntiAlias(true);
if (mShape == SHAPE_ROUND) {
canvas.drawRoundRect(mRect, mShapeRadius, mShapeRadius, mPaint);
canvas.drawRoundRect(mRect, mShapeRadius, mShapeRadius, newPaint);
} else {
canvas.drawCircle(mRect.centerX(), mRect.centerY(), Math.min(mRect.width(), mRect.height())/ 2, mPaint);
canvas.drawCircle(mRect.centerX(), mRect.centerY(), Math.min(mRect.width(), mRect.height())/ 2, newPaint);
}
}
@Override
public void setAlpha(@IntRange(from = 0, to = 255) int alpha) {
mPaint.setAlpha(alpha);
}
@Override
public void setColorFilter(@Nullable ColorFilter colorFilter) {
mPaint.setColorFilter(colorFilter);
}
@Override
public int getOpacity() {
return PixelFormat.TRANSLUCENT;
}
public static void setShadowHelper(View view, Drawable drawable) {
view.setLayerType(View.LAYER_TYPE_SOFTWARE, null);
ViewCompat.setBackground(view, drawable);
}
public void into(View view){
if (view == null){
return;
}
view.setLayerType(View.LAYER_TYPE_SOFTWARE, null);
ViewCompat.setBackground(view, this);
}
}
