前言
在开发中，圆角和阴影效果是很常用的。实现的方法也很多，比如通过xml自定义shape，比如通过代码继承drawable，还有通过第三发框架实现。但是使用起来还是有些许不灵活，所以我们通过自定义子view的属性，然后通过父布局来控制子view的圆角，阴影等属性。
继承ConstraintLayout
开发中复杂的布局基本上都可以通过ConstraintLayout实现，所以我们继承ConstraintLayout实现一个EasyConstraintLayout能够为子view添加圆角和阴影效果。
public class EasyConstraintLayout extends ConstraintLayout {
public EasyConstraintLayout(Context context, AttributeSet attrs) {
super(context, attrs);
}
@Override
public LinearLayout.LayoutParams generateLayoutParams(AttributeSet attrs) {
return new LayoutParams(getContext(), attrs);
}
@Override
protected boolean checkLayoutParams(ViewGroup.LayoutParams p) {
return p instanceof LayoutParams;
}
}
重写了两个方法，我们要用这些方法实现子view自定义属性的读取，在此之前要在xml中自定义一些属性
<?xml version="1.0" encoding="utf-8"?>
<resources>
<!--为了方便扩展其他layout，定义在外层，命名以layout_开头，否则lint会报红警告-->
<attr name="layout_radius" format="dimension" />
<attr name="layout_shadowColor" format="color" />
<attr name="layout_shadowEvaluation" format="dimension" />
<attr name="layout_shadowDx" format="dimension" />
<attr name="layout_shadowDy" format="dimension" />
<!--用统一一个EasyLayout，用于封装读取自定义属性-->
<declare-styleable name="EasyLayout">
<attr name="layout_radius" />
<attr name="layout_shadowColor" />
<attr name="layout_shadowEvaluation" />
<attr name="layout_shadowDx" />
<attr name="layout_shadowDy" />
</declare-styleable>
<!--和EasyLayout属性列表一样，但是命名要以XXX_Layout格式，这样开发工具会提示自定义属性-->
<declare-styleable name="EasyConstraintLayout_Layout">
<attr name="layout_radius" />
<attr name="layout_shadowColor" />
<attr name="layout_shadowEvaluation" />
<attr name="layout_shadowDx" />
<attr name="layout_shadowDy" />
</declare-styleable>
</resources>
重写LayoutParams，读取子View自定义属性
在EasyConstraintLayout内部定义一个静态类LayoutParams继承ConstraintLayout.LayoutParams，然后在构造方法中读取上面自定义的属性。我们通过裁剪的方式实现圆角效果，因此还有要获取子view的位置和大小。
static class LayoutParams extends ConstraintLayout.LayoutParams
implements EasyLayoutParams{
private LayoutParamsData data;
public LayoutParams(Context c, AttributeSet attrs) {
super(c, attrs);
data = new LayoutParamsData(c, attrs);
}
@Override
public LayoutParamsData getData() {
return data;
}
}
public interface EasyLayoutParams {
LayoutParamsData getData();
}
public class LayoutParamsData {
int radius;
int shadowColor;
int shadowDx;
int shadowDy;
int shadowEvaluation;
public LayoutParamsData(Context context, AttributeSet attrs) {
TypedArray a = context.obtainStyledAttributes(attrs, R.styleable.EasyLayout);
radius = a.getDimensionPixelOffset(R.styleable.EasyLayout_layout_radius, 0);
shadowDx = a.getDimensionPixelOffset(R.styleable.EasyLayout_layout_shadowDx, 0);
shadowDy = a.getDimensionPixelOffset(R.styleable.EasyLayout_layout_shadowDy, 0);
shadowColor = a.getColor(R.styleable.EasyLayout_layout_shadowColor, 0x99999999);
shadowEvaluation = a.getDimensionPixelOffset(R.styleable.EasyLayout_layout_shadowEvaluation, 0);
a.recycle();
}
}
圆角和阴影实现原理
因为我们是通过父布局控制子view的圆角和阴影行为，所以我们重写drawChild来实现，drawChild之前，先通过paint的ShadowLayer属性把子View的阴影先画上，这个阴影需要裁剪掉子view自身的大小位置。然后再画子view，并且裁剪圆角部分，最终实现圆角阴影效果。裁剪起初我们想到的是通过canvas的clipPath方法实现，但是发现会有很大的锯齿。所以改用paint的xfermode来裁剪阴影和子view。
onLayout初始化裁剪信息
在EasyConstraintLayout中初始化LayoutParamsData的paths
@Override
protected void onLayout(boolean changed, int left, int top, int right, int bottom) {
super.onLayout(changed, left, top, right, bottom);
for (int i = 0, size = getChildCount(); i < size; i++) {
View v = getChildAt(i);
ViewGroup.LayoutParams lp = v.getLayoutParams();
if(lp instanceof EasyLayoutParams){
EasyLayoutParams elp = (EasyLayoutParams) lp;
elp.getData().initPaths(v);
}
}
}
在LayoutParamsData中将裁剪阴影的path和裁剪子view的保存起来，新增两个属性
public class LayoutParamsData {
Path widgetPath;
Path clipPath;
boolean needClip;
boolean hasShadow;
public LayoutParamsData(Context context, AttributeSet attrs) {
…
needClip = radius > 0;
hasShadow = shadowEvaluation > 0;
}
public void initPaths(View v) {
widgetPath = new Path();
clipPath = new Path();
clipPath.addRect(widgetRect, Path.Direction.CCW);
clipPath.addRoundRect(
widgetRect,
radius,
radius,
Path.Direction.CW
);
widgetPath.addRoundRect(
widgetRect,
radius,
radius,
Path.Direction.CW
);
}
}
drawChild中画阴影，裁剪出圆角
我们在EasyConstraintLayout中初始化paint，并且关闭硬件加速，然后在drawChild中实现阴影逻辑，最终代码如下。
public class EasyConstraintLayout extends ConstraintLayout {
private Paint shadowPaint;
private Paint clipPaint;
public EasyConstraintLayout(Context context, AttributeSet attrs) {
super(context, attrs);
shadowPaint = new Paint();
shadowPaint.setAntiAlias(true);
shadowPaint.setDither(true);
shadowPaint.setFilterBitmap(true);
shadowPaint.setStyle(Paint.Style.FILL);
clipPaint = new Paint();
clipPaint.setAntiAlias(true);
clipPaint.setDither(true);
clipPaint.setFilterBitmap(true);
clipPaint.setStyle(Paint.Style.FILL);
setLayerType(View.LAYER_TYPE_SOFTWARE, null);
}
@Override
public ConstraintLayout.LayoutParams generateLayoutParams(AttributeSet attrs) {
return new LayoutParams(getContext(), attrs);
}
@Override
protected boolean checkLayoutParams(ViewGroup.LayoutParams p) {
return p instanceof LayoutParams;
}
@Override
protected void onLayout(boolean changed, int left, int top, int right, int bottom) {
super.onLayout(changed, left, top, right, bottom);
for (int i = 0, size = getChildCount(); i < size; i++) {
View v = getChildAt(i);
ViewGroup.LayoutParams lp = v.getLayoutParams();
if (lp instanceof EasyLayoutParams) {
EasyLayoutParams elp = (EasyLayoutParams) lp;
elp.getData().initPaths(v);
}
}
}
@Override
protected boolean drawChild(Canvas canvas, View child, long drawingTime) {
ViewGroup.LayoutParams lp = child.getLayoutParams();
boolean ret = false;
if (lp instanceof EasyLayoutParams) {
EasyLayoutParams elp = (EasyLayoutParams) lp;
LayoutParamsData data = elp.getData();
if (isInEditMode()) {//预览模式采用裁剪
canvas.save();
canvas.clipPath(data.widgetPath);
ret = super.drawChild(canvas, child, drawingTime);
canvas.restore();
return ret;
}
if (!data.hasShadow && !data.needClip)
return super.drawChild(canvas, child, drawingTime);
//为解决锯齿问题，正式环境采用xfermode
if (data.hasShadow) {
int count = canvas.saveLayer(null, null, Canvas.ALL_SAVE_FLAG);
shadowPaint.setShadowLayer(data.shadowEvaluation, data.shadowDx, data.shadowDy, data.shadowColor);
shadowPaint.setColor(data.shadowColor);
canvas.drawPath(data.widgetPath, shadowPaint);
shadowPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.DST_OUT));
shadowPaint.setColor(Color.WHITE);
canvas.drawPath(data.widgetPath, shadowPaint);
shadowPaint.setXfermode(null);
canvas.restoreToCount(count);
}
if (data.needClip) {
int count = canvas.saveLayer(child.getLeft(), child.getTop(), child.getRight(), child.getBottom(), null, Canvas.ALL_SAVE_FLAG);
ret = super.drawChild(canvas, child, drawingTime);
clipPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.CLEAR));
clipPaint.setColor(Color.WHITE);
canvas.drawPath(data.clipPath, clipPaint);
clipPaint.setXfermode(null);
canvas.restoreToCount(count);
}
}
return ret;
}
static class LayoutParams extends ConstraintLayout.LayoutParams implements EasyLayoutParams {
private LayoutParamsData data;
public LayoutParams(Context c, AttributeSet attrs) {
super(c, attrs);
data = new LayoutParamsData(c, attrs);
}
@Override
public LayoutParamsData getData() {
return data;
}
}
}
使用方法
<?xml version="1.0" encoding="utf-8"?>
<io.github.iamyours.easylayout.EasyConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">
<View
android:id="@+id/v_back"
android:layout_width="match_parent"
android:layout_height="150dp"
android:layout_margin="10dp"
android:background="#fff"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:layout_radius="4dp"
app:layout_shadowColor="#3ccc"
app:layout_shadowEvaluation="15dp" />
<ImageView
android:id="@+id/iv_head"
android:layout_width="80dp"
android:layout_height="80dp"
android:layout_gravity="center_horizontal"
android:layout_marginLeft="10dp"
android:background="#eee"
app:layout_constraintBottom_toBottomOf="@id/v_back"
app:layout_constraintLeft_toLeftOf="@id/v_back"
app:layout_constraintTop_toTopOf="@id/v_back"
app:layout_radius="40dp"
app:layout_shadowColor="#5f00"
app:layout_shadowEvaluation="8dp" />
<View
android:layout_width="200dp"
android:layout_height="200dp"
android:layout_marginTop="30dp"
android:background="#ccc"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintTop_toBottomOf="@id/v_back"
app:layout_radius="30dp"
app:layout_shadowColor="#8f0f"
app:layout_shadowDx="4dp"
app:layout_shadowDy="4dp"
app:layout_shadowEvaluation="10dp" />
</io.github.iamyours.easylayout.EasyConstraintLayout>
最终效果如下：
项目地址: https://github.com/iamyours/EasyWidgets
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