《Android 进阶（三）》 自定义View之支持Gravity的ViewGroup

1. 前言

前面两篇博客主要是介绍直接继承View后复写onDraw方法来实现一些不规则图形的绘制，来达到满足不同自定义View的需求，更注重的是图形的绘制变换和效果展示，前两天学习一些自定义ViewGroup的相关内容，分享一下。

2. 目标

支持Gravity的ViewGroup。

支持的Gravity的种类：左上，右上，左下，右下，中心。

3. 实现步骤

自定义属性：custom_gravity自定义属性的取值范围：1－5(topleft, topright, bottomleft, bottomright, center)自定义LayoutParam。参考LinearLayout，RelativeLayout等等复写onMeasure， onLayout复写LayoutParam相关的几个方法

4. 几点提醒

onMeasure使用来确定子view的大小的，没有那么神秘，就是根据ViewGroup的大小和子View的LayoutParam来确定子View应该有的大小。通过 MeasureSpec.makeMeasureSpec的方式生成MeasureSpec，通过调用子View的measure方法，把数据传递给子View，方便确定大小。onLayout方法同来确定子View的位置，传入的参数是当前View Group的上下左上角和右下角的位置，通过子View的属性值和一些其他判断条件，来计算子View应该摆放在哪个位置，然后通过调用子View的layout方法来摆放。自定义LayoutParam。需要复写几个方法

5. 代码实现

5.1 自定义属性

<declare-styleable name="CustomViewGroup"> <attr name="custom_gravity"/> </declare-styleable> <attr name="custom_gravity"> <flag name="topleft" value="1"/> <flag name="topright" value="2"/> <flag name="bottomleft" value="3"/> <flag name="bottomright" value="4"/> <flag name="center" value="5"/> </attr>

5.2 CustomViewGroup

代码写的比较简单，方便理解，把每个子View的大小全部设置成相同的大小。

public class CustomViewGroup extends ViewGroup { public CustomViewGroup(Context context) { super(context); } public CustomViewGroup(Context context, AttributeSet attrs) { super(context, attrs); } public CustomViewGroup(Context context, AttributeSet attrs, int defStyleAttr) { super(context, attrs, defStyleAttr); } @Override protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) { super.onMeasure(widthMeasureSpec, heightMeasureSpec); int widthSize = MeasureSpec.getSize(widthMeasureSpec); int heightSize = MeasureSpec.getSize(heightMeasureSpec); /** * 每个子View的大小都设置成相同大小 */ for (int i = 0; i < getChildCount(); i++) { View child = getChildAt(i); int mode = MeasureSpec.EXACTLY; int childWidth = widthSize / 4; int childHeight = heightSize / 4; child.measure(MeasureSpec.makeMeasureSpec(childWidth, mode), MeasureSpec.makeMeasureSpec(childHeight, mode)); } } @Override protected void onLayout(boolean changed, int l, int t, int r, int b) { for (int i = 0; i < getChildCount(); i++) { View child = getChildAt(i); int width = child.getMeasuredWidth(); int height = child.getMeasuredHeight(); final LayoutParams lp = (LayoutParams) child.getLayoutParams(); int gravity = lp.gravity; switch (gravity) { case LayoutParams.TOPLEFT_GRAVITY: child.layout(l, t, width, height); break; case LayoutParams.TOPRIGHT_GRAVITY: child.layout(r - width, t, r, height); break; case LayoutParams.BOTTOMLEFT_GRAVITY: child.layout(l, b - height, width, b); break; case LayoutParams.BOTTOMRIGHT_GRAVITY: child.layout(r - width, b - height, r, b); break; case LayoutParams.CENTER_GRAVITY: child.layout((r - width) / 2, (b - height) / 2, (r + width) / 2, (b + height) / 2); break; default: break; } } } @Override public ViewGroup.LayoutParams generateLayoutParams(AttributeSet attrs) { return new LayoutParams(getContext(), attrs); } @Override protected ViewGroup.LayoutParams generateLayoutParams(ViewGroup.LayoutParams p) { return new LayoutParams(p); } @Override protected ViewGroup.LayoutParams generateDefaultLayoutParams() { return new LayoutParams(ViewGroup.LayoutParams.WRAP_CONTENT, ViewGroup.LayoutParams.WRAP_CONTENT, 1); } @Override protected boolean checkLayoutParams(ViewGroup.LayoutParams p) { return p instanceof LayoutParams; } public static class LayoutParams extends ViewGroup.LayoutParams { public static final int UNSPECIFIED_GRAVITY = -1; public static final int TOPLEFT_GRAVITY = 1; public static final int TOPRIGHT_GRAVITY = 2; public static final int BOTTOMLEFT_GRAVITY = 3; public static final int BOTTOMRIGHT_GRAVITY = 4; public static final int CENTER_GRAVITY = 5; public int gravity = UNSPECIFIED_GRAVITY; public LayoutParams(@NonNull Context c, @Nullable AttributeSet attrs) { super(c, attrs); final TypedArray a = c.obtainStyledAttributes(attrs, R.styleable.CustomViewGroup); gravity = a.getInt(R.styleable.CustomViewGroup_custom_gravity, UNSPECIFIED_GRAVITY); a.recycle(); } public LayoutParams(int width, int height, int gravity) { super(width, height); this.gravity = gravity; } public LayoutParams(@NonNull ViewGroup.LayoutParams source) { super(source); this.gravity = TOPLEFT_GRAVITY; } public LayoutParams(@NonNull LayoutParams source) { super(source); this.gravity = source.gravity; } } }

6. 效果图

7. 源代码

源代码还是上传到Github CustomViewDemo

onlyloveyd 认证博客专家 Android Kotlin OpenCV 个人公众号【OpenCV or Android】，热爱Android、Kotlin、Flutter和OpenCV。毕业于华中科技大学计算机专业，曾就职于华为武汉研究所。目前在三线小城市生活，专注Android、OpenCV、Kotlin、Flutter等有趣的技术。