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;
}
}
}
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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>
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