一、需求来源：
设计师要求还原设计的阴影，下面是sketch原型参数：
圆角：8px
外阴影：
Offset: 0px 1px
X Y
Effect: 10px 0px
Blur Spread
颜色： #135B90D0
二、Android本身控件自带阴影效果无法还原
Google的Material Design中对于阴影的定义是：海拔高度是相对深度或距离，是两个表面在 Z 轴上的距离。
实现方式：
第一种方式：elevation属性
View的大小位置都是通过x，y确定的，而现在有了z轴的概念，而这个z值就是View的高度（elevation），而高度决定了阴影（shadow）的大小。第二种方式：CardView自带属性
card_view:cardElevation 阴影的大小
card_view:cardMaxElevation 阴影最大高度
card_view:cardBackgroundColor 卡片的背景色
card_view:cardCornerRadius 卡片的圆角大小
card_view:contentPadding 卡片内容于边距的间隔
- 第三种方式：
设置边框为shape，通过layer-list实现层次感
<layer-list xmlns:android="http://schemas.android.com/apk/res/android">
<item>
<shape android:shape="oval">
<padding
android:bottom="2dp"
android:left="2dp"
android:right="2dp"
android:top="2dp" />
<solid android:color="#0DF3F3F3" />
<corners android:radius="8dp" />
</shape>
</item>
<item>
<shape
android:layout_width="wrap_content"
android:shape="oval">
<padding
android:bottom="2dp"
android:left="2dp"
android:right="2dp"
android:top="2dp" />
<solid android:color="#10F3F3F3" />
<corners android:radius="8dp" />
</shape>
</item>
<item>
<shape android:shape="oval">
<padding
android:bottom="2dp"
android:left="2dp"
android:right="2dp"
android:top="2dp" />
<solid android:color="#15F3F3F3" />
<corners android:radius="8dp" />
</shape>
</item>
<item>
<shape android:shape="oval">
<padding
android:bottom="2dp"
android:left="2dp"
android:right="2dp"
android:top="2dp" />
<solid android:color="#20F3F3F3" />
<corners android:radius="8dp" />
</shape>
</item>
<item>
<shape android:shape="oval">
<padding
android:bottom="2dp"
android:left="2dp"
android:right="2dp"
android:top="2dp" />
<solid android:color="#25F3F3F3" />
<corners android:radius="8dp" />
</shape>
</item>
<item>
<shape android:shape="oval">
<solid android:color="#FFFFFF" />
</shape>
</item>
</layer-list>
三、使用Android画笔Paint来实现
- 第四种方式（属性一一对应设计稿）：
/**
* 使用圆角时，应设置圆角相同的background
*/
public class ShadowRelativeLayout extends RelativeLayout {
/**
* 阴影的颜色
*/
private int shadowColor = Color.argb(90, 0, 0, 0);
/**
* 高斯模糊的模糊半径,值越大越模糊，越小越清晰,
*/
private float shadowBlur = 30;
/**
* 阴影的圆角
*/
private float shadowRadius = 0;
/**
* 阴影的偏移
*/
private float shadowDx = 0;
private float shadowDy = 0;
public ShadowRelativeLayout(@NonNull Context context) {
this(context, null);
}
public ShadowRelativeLayout(@NonNull Context context,
@Nullable AttributeSet attrs) {
this(context, attrs, 0);
}
public ShadowRelativeLayout(@NonNull Context context, @Nullable AttributeSet attrs,
int defStyleAttr) {
super(context, attrs, defStyleAttr);
dealAttrs(context, attrs);
setPaint();
}
private Paint mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
@Override
public void draw(Canvas canvas) {
setInsetBackground();
canvas.drawRoundRect(getRectF(), shadowRadius, shadowRadius, mPaint);
super.draw(canvas);
}
private boolean setInsetBackground() {
Drawable background = getBackground();
if (background == null || background instanceof InsetDrawable) {
return false;
}
InsetDrawable drawable =
new InsetDrawable(background, getPaddingLeft(), getPaddingTop(),
getPaddingRight(), getPaddingBottom());
setBackground(drawable);
return true;
}
private RectF getRectF() {
return new RectF(getPaddingLeft() + shadowDx, getPaddingTop() + shadowDy,
getWidth() - getPaddingRight() + shadowDx,
getHeight() - getPaddingBottom() + shadowDy);
}
private void dealAttrs(Context context, AttributeSet attrs) {
TypedArray typedArray = context.obtainStyledAttributes(attrs, R.styleable.ShadowRelativeLayout);
if (typedArray != null) {
shadowColor = typedArray.getColor(R.styleable.ShadowRelativeLayout_shadow_color, shadowColor);
shadowRadius =
typedArray.getDimension(R.styleable.ShadowRelativeLayout_shadow_radius, shadowRadius);
shadowBlur =
typedArray.getDimension(R.styleable.ShadowRelativeLayout_shadow_blur, shadowBlur);
shadowDx = typedArray.getDimension(R.styleable.ShadowRelativeLayout_shadow_dx, shadowDx);
shadowDy = typedArray.getDimension(R.styleable.ShadowRelativeLayout_shadow_dy, shadowDy);
typedArray.recycle();
}
}
private void setPaint() {
setLayerType(View.LAYER_TYPE_SOFTWARE, null); // 关闭硬件加速,阴影才会绘制
// todo 从AttributeSet获取设置的值
mPaint.setAntiAlias(true);
mPaint.setColor(shadowColor);
mPaint.setMaskFilter(new BlurMaskFilter(shadowBlur, BlurMaskFilter.Blur.NORMAL));
}
@Override
public boolean isOpaque() { //纯色或图片做背景时,draw之前会有黑底色，
return false;
}
}
attrs.xml
<?xml version="1.0" encoding="utf-8"?>
<resources>
<declare-styleable name="ShadowRelativeLayout">
<attr format="color" name="shadow_color"/>
<attr format="dimension" name="shadow_radius"/>
<attr format="dimension" name="shadow_blur"/>
<attr format="dimension" name="shadow_dx"/>
<attr format="dimension" name="shadow_dy"/>
</declare-styleable>
</resources>
使用范例（属性完美映射设计稿）：
<ShadowRelativeLayout
android:layout_width="180dp"
android:layout_height="100dp"
android:background="@drawable/shape_round_white_dp8"
android:padding="10dp"
bind:shadow_blur="10dp"
bind:shadow_color="#135B90D0"
bind:shadow_dx="0dp"
bind:shadow_dy="1dp"
bind:shadow_radius="8dp">
<ImageView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_centerInParent="true"
android:layout_gravity="center"
android:scaleType="center"
android:src="@drawable/light" />
</ShadowRelativeLayout>
