自定义ViewGroup

时间 2019-12-02

标签自定义 viewgroup 繁體版

原文原文链接

关于View的基本知识和如何自定义View请见html

自定义View - http://www.javashuo.com/article/p-bnjbkrpi-bo.htmljava

ViewGroup的职责是啥？

ViewGroup至关于一个放置View的容器，而且咱们在写布局xml的时候，会告诉容器（凡是以layout为开头的属性，都是用于告诉容器的），咱们的宽度layout_width、高度layout_height、对齐方式layout_gravity、内边距layout_maring等。因此ViewGroup的智能为：给childView计算出建议的宽和高的测量模式；决定childView的位置。（由于childView宽和高能够设置为wrap_content，这样只有childView才能计算出本身的宽和高，因此这里给出的建议宽和高）android

View的职责是啥？

View的职责就是根据测量模式和ViewGroup给出的建议的宽和高，计算出本身的宽和高；同事还有个更重要的职责：在ViewGroup为其指定的区域内绘制本身的形态。canvas

ViewGroup和LayoutParams之间的关系？

每一个ViewGroup须要指定一个LayoutParams，用于肯定它的childView支持哪些属性。不一样的ViewGroup指定的LayoutParams是不一样的，包含的属性也不尽相同。ide

View的3种测量模式

EXACTLY、AT_MOST、UNSPECIFIED布局

从API角度进行浅析

上面叙述了ViewGroup和View的职责，下面从API角度进行浅析。this

View须要根据ViewGroup传入的测量值和模式，对本身宽高进行肯定（onMeasure中完成），而后在onDraw中完成对本身的绘制。spa

ViewGroup须要给View传入view的测量值和模式（onMeasure中完成），并且对于此ViewGroup的父布局，本身也须要在onMeasure中完成对本身宽和高的肯定。此外，须要在onLayout中完成对其childView的位置的指定。.net

Demo

定义一个ViewGroup，内部能够传入0到4个childView，分别依次显示在左上角、右上角、左下角、右下角。同时在中央绘制一个圆。code

/**
 * Created by xupeng on 16/12/26.
 */

public class MyCustomViewGroup extends ViewGroup {

    private Paint mPaint;

    public MyCustomViewGroup(Context context) {
        super(context);
        init();
    }

    public MyCustomViewGroup(Context context, AttributeSet attrs) {
//        super(context, attrs);
        this(context);
    }

    private void init() {
        setWillNotDraw(false);
        mPaint = new Paint();
        mPaint.setColor(Color.RED);
    }

    @Override
    public LayoutParams generateLayoutParams(AttributeSet attrs) {
        return new MarginLayoutParams(getContext(), attrs);
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        /**
         * 得到此ViewGroup上级容器为其推荐的宽和高,以及计算模式
         */
        int widthSize = MeasureSpec.getSize(widthMeasureSpec);
        int widthMode = MeasureSpec.getMode(widthMeasureSpec);
        int heightSize = MeasureSpec.getSize(heightMeasureSpec);
        int heightMode = MeasureSpec.getMode(heightMeasureSpec);

        // 计算出全部的children的宽和高
        measureChildren(widthMeasureSpec, heightMeasureSpec);

        /**
         * 记录若是是wrap_content设置的宽和高
         */
        int width = 0;
        int height = 0;

        int cCount = getChildCount();

        int cWidth = 0;
        int cHeight = 0;
        MarginLayoutParams cParams = null;

        // 用于计算左边两个childView的高度
        int lHeight = 0;

        // 用于计算右边两个childView的高度,最终高度取二者之间大值
        int rHeight = 0;

        // 用于计算上边两个childView的宽度
        int tWidth = 0;

        // 用于计算下边两个childView的宽度,最重宽度取二者之间大值
        int bWidth = 0;

        /**
         * 根据childView计算得出宽和高,以及设置的margin计算容器的宽和高,主要用于容器是wrap_content时
         */
        for (int i = 0; i < cCount; i++) {
            View childView = getChildAt(i);
            cWidth = childView.getMeasuredWidth();
            cHeight = childView.getMeasuredHeight();
            cParams = (MarginLayoutParams) childView.getLayoutParams();

            // 上面两个childView
            if (i == 0 || i == 1) {
                tWidth += cWidth + cParams.leftMargin + cParams.rightMargin;
            }

            // 下面两个childView
            if (i == 2 || i == 3) {
                bWidth += cWidth + cParams.leftMargin + cParams.rightMargin;
            }

            if (i == 0 || i == 2) {
                lHeight += cHeight + cParams.topMargin + cParams.bottomMargin;
            }

            if (i == 1 || i == 3) {
                rHeight += cHeight + cParams.topMargin + cParams.bottomMargin;
            }

        }

        width = Math.max(tWidth, bWidth);
        height = Math.max(lHeight, rHeight);

        setMeasuredDimension((widthMode == MeasureSpec.EXACTLY) ? widthSize : width,
                (heightMode == MeasureSpec.EXACTLY) ? heightSize : height);

//        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
    }

    @Override
    protected void onLayout(boolean changed, int l, int t, int r, int b) {
        int cCount = getChildCount();
        int cWidth = 0;
        int cHeight = 0;
        MarginLayoutParams cParams = null;

        /**
         * 遍历全部childView根据其宽和高,以及margin进行布局
         */
        for (int i = 0; i < cCount; i++) {
            View childView = getChildAt(i);
            cWidth = childView.getMeasuredWidth();
            cHeight = childView.getMeasuredHeight();
            cParams = (MarginLayoutParams) childView.getLayoutParams();

            int cl = 0, ct = 0, cb = 0, cr = 0;

            switch (i) {
                case 0:
                    cl = cParams.leftMargin;
                    ct = cParams.topMargin;
                    break;
                case 1:
                    cl = getWidth() - cWidth - cParams.rightMargin;
                    ct = cParams.topMargin;
                    break;
                case 2:
                    cl = cParams.leftMargin;
                    ct = getHeight() - cHeight - cParams.bottomMargin;
                    break;
                case 3:
                    cl = getWidth() - cWidth - cParams.rightMargin;
                    ct = getHeight() - cHeight - cParams.bottomMargin;
                    break;
            }

            cr = cl + cWidth;
            cb = cHeight + ct;
            childView.layout(cl, ct, cr, cb);
        }
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        int width = getWidth();
        int measureWidth = getMeasuredWidth();
        requestLayout();
        int measureWidthAndState = getMeasuredWidthAndState();
        canvas.drawCircle(getMeasuredWidth() / 2, getMeasuredHeight() / 2, 100 , mPaint);
//        invalidate();
    }

<?xml version="1.0" encoding="utf-8"?>
<com.gnepux.sdkusage.widget.MyCustomViewGroup xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/activity_custom_view_group"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="#ffff00"
    tools:context="com.gnepux.sdkusage.activity.CustomViewGroupActivity">

    <com.gnepux.sdkusage.widget.MyCustomView
        android:layout_width="50dp"
        android:layout_height="50dp"
        android:text="1"
        android:gravity="center"
        android:textColor="#ffffff"
        android:background="#ff0000"/>

    <com.gnepux.sdkusage.widget.MyCustomView
        android:layout_width="50dp"
        android:layout_height="50dp"
        android:text="2"
        android:gravity="center"
        android:textColor="#ffffff"
        android:background="#00ff00"/>

    <com.gnepux.sdkusage.widget.MyCustomView
        android:layout_width="50dp"
        android:layout_height="50dp"
        android:text="3"
        android:gravity="center"
        android:textColor="#ffffff"
        android:background="#0000ff"/>

    <com.gnepux.sdkusage.widget.MyCustomView
        android:layout_width="50dp"
        android:layout_height="50dp"
        android:text="4"
        android:gravity="center"
        android:textColor="#ffffff"
        android:background="#ff00ff"/>

</com.gnepux.sdkusage.widget.MyCustomViewGroup>

参考连接：

View原理简介

http://blog.csdn.net/u011733020/article/details/50849475

帮你搞定Android自定义View

http://www.jianshu.com/p/84cee705b0d3

Android手把手教您自定义ViewGroup

http://blog.csdn.net/lmj623565791/article/details/38339817/

为何自定义ViewGroup ondraw方法不会被调用

http://www.jcodecraeer.com/a/anzhuokaifa/androidkaifa/2014/1014/1765.html

关于getMeasuredHeight和getHeight区别（getMeasureHeight是xml或代码中制定的测量高度，setMeasuredHeight; getHeight是实际显示出来的高度，经过view.layout()方即可以改变其值）

http://blog.csdn.net/qq_29951983/article/details/50571840