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;
}
}
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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>
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