View绘制的三部曲,  测量,布局,绘画
今天我们分析测量过程

view的测量是从ViewRootImpl发起的,View需要重绘,都是发送请求给ViewRootImpl,然后他组织重绘
在重绘的过程中,有一步就是测量,通过代码来分析测量过程

    private boolean measureHierarchy(final View host, final WindowManager.LayoutParams lp,
            final Resources res, final int desiredWindowWidth, final int desiredWindowHeight) {
        int childWidthMeasureSpec;
        int childHeightMeasureSpec;
        boolean windowSizeMayChange = false;

        if (DEBUG_ORIENTATION || DEBUG_LAYOUT) Log.v(TAG,
                "Measuring " + host + " in display " + desiredWindowWidth
                + "x" + desiredWindowHeight + "...");

        boolean goodMeasure = false;
        if (lp.width == ViewGroup.LayoutParams.WRAP_CONTENT) {
            // On large screens, we don't want to allow dialogs to just
            // stretch to fill the entire width of the screen to display
            // one line of text.  First try doing the layout at a smaller
            // size to see if it will fit.
            final DisplayMetrics packageMetrics = res.getDisplayMetrics();
            res.getValue(com.android.internal.R.dimen.config_prefDialogWidth, mTmpValue, true);
            int baseSize = 0;
            if (mTmpValue.type == TypedValue.TYPE_DIMENSION) {
                baseSize = (int)mTmpValue.getDimension(packageMetrics);
            }
            if (DEBUG_DIALOG) Log.v(TAG, "Window " + mView + ": baseSize=" + baseSize);
            if (baseSize != 0 && desiredWindowWidth > baseSize) {
                //获取测量的规格,是一个32位的二进制数值,前两位标识mode,后30位表示view的长/宽
                childWidthMeasureSpec = getRootMeasureSpec(baseSize, lp.width);
                childHeightMeasureSpec = getRootMeasureSpec(desiredWindowHeight, lp.height);
                //向DecorView发起重绘
                performMeasure(childWidthMeasureSpec, childHeightMeasureSpec);
                if (DEBUG_DIALOG) Log.v(TAG, "Window " + mView + ": measured ("
                        + host.getMeasuredWidth() + "," + host.getMeasuredHeight() + ")");
                if ((host.getMeasuredWidthAndState()&View.MEASURED_STATE_TOO_SMALL) == 0) {
                    goodMeasure = true;
                } else {
                    // Didn't fit in that size... try expanding a bit.
                    baseSize = (baseSize+desiredWindowWidth)/2;
                    if (DEBUG_DIALOG) Log.v(TAG, "Window " + mView + ": next baseSize="
                            + baseSize);
                    childWidthMeasureSpec = getRootMeasureSpec(baseSize, lp.width);
                    performMeasure(childWidthMeasureSpec, childHeightMeasureSpec);
                    if (DEBUG_DIALOG) Log.v(TAG, "Window " + mView + ": measured ("
                            + host.getMeasuredWidth() + "," + host.getMeasuredHeight() + ")");
                    if ((host.getMeasuredWidthAndState()&View.MEASURED_STATE_TOO_SMALL) == 0) {
                        if (DEBUG_DIALOG) Log.v(TAG, "Good!");
                        goodMeasure = true;
                    }
                }
            }
        }

        if (!goodMeasure) {
            childWidthMeasureSpec = getRootMeasureSpec(desiredWindowWidth, lp.width);
            childHeightMeasureSpec = getRootMeasureSpec(desiredWindowHeight, lp.height);
            performMeasure(childWidthMeasureSpec, childHeightMeasureSpec);
            if (mWidth != host.getMeasuredWidth() || mHeight != host.getMeasuredHeight()) {
                windowSizeMayChange = true;
            }
        }

        if (DBG) {
            System.out.println("======================================");
            System.out.println("performTraversals -- after measure");
            host.debug();
        }

        return windowSizeMayChange;
    }

这个函数通过getRootMeasureSpec方法,获取测量规格,然后调用performMeasure方法开始分发给整个的view树。

    private static int getRootMeasureSpec(int windowSize, int rootDimension) {
        int measureSpec;
        switch (rootDimension) {

        case ViewGroup.LayoutParams.MATCH_PARENT:
            // Window can't resize. Force root view to be windowSize.
            measureSpec = MeasureSpec.makeMeasureSpec(windowSize, MeasureSpec.EXACTLY);
            break;
        case ViewGroup.LayoutParams.WRAP_CONTENT:
            // Window can resize. Set max size for root view.
            measureSpec = MeasureSpec.makeMeasureSpec(windowSize, MeasureSpec.AT_MOST);
            break;
        default:
            // Window wants to be an exact size. Force root view to be that size.
            measureSpec = MeasureSpec.makeMeasureSpec(rootDimension, MeasureSpec.EXACTLY);
            break;
        }
        return measureSpec;
    }

通过MeasureSpec的makeMeasureSpec方法来生成测量规格,先判断出布局是 match_parent 或者是 wrap_content,或者是确定的数值
 然后把windowSize传递下去。

    public static int makeMeasureSpec(int size, int mode) {
            if (sUseBrokenMakeMeasureSpec) {
                return size + mode;
            } else {
                return (size & ~MODE_MASK) | (mode & MODE_MASK);
            }
    }

API大于17的都会走else判断,这块我分析一下计算结果。有助于理解后边的运算

makeMeasureSpec的运算结果是一个32位的二进制数值,前2位表示测量的规格 EXACTLY/AT_most 后30位表示 windowSize,举个运算例子    
 size=320,mode=EXACTLY,换算成二进制就是下边的两串值
 size=0000 0000 0000 0000 0000 0001 0100 0000
 mode=0100 0000 0000 0000 0000 0000 0000 0000
 mask=1100 0000 0000 0000 0000 0000 0000 0000
 最后用与运算整合size和mode
 0000 0000 0000 0000 0000 0001 0100 0000 |
 0100 0000 0000 0000 0000 0000 0000 0000 =
 0100 0000 0000 0000 0000 0001 0100 0000

    private void performMeasure(int childWidthMeasureSpec, int childHeightMeasureSpec) {
        Trace.traceBegin(Trace.TRACE_TAG_VIEW, "measure");
        try {
            mView.measure(childWidthMeasureSpec, childHeightMeasureSpec);
        } finally {
            Trace.traceEnd(Trace.TRACE_TAG_VIEW);
        }
    }

这个mView就是我们在window类中组合出来的DecorView,这个方法调用了view的measure方法,measure会调用OnMeasure方法,然后就实现了整个view树的测量工作

    public final void measure(int widthMeasureSpec, int heightMeasureSpec) {
        boolean optical = isLayoutModeOptical(this);
        if (optical != isLayoutModeOptical(mParent)) {
            Insets insets = getOpticalInsets();
            int oWidth  = insets.left + insets.right;
            int oHeight = insets.top  + insets.bottom;
            widthMeasureSpec  = MeasureSpec.adjust(widthMeasureSpec,  optical ? -oWidth  : oWidth);
            heightMeasureSpec = MeasureSpec.adjust(heightMeasureSpec, optical ? -oHeight : oHeight);
        }

        // 这块又把宽的测量规格和高的测量规格拼接在了一起,作为缓存中的key
        long key = (long) widthMeasureSpec << 32 | (long) heightMeasureSpec & 0xffffffffL;
        if (mMeasureCache == null) mMeasureCache = new LongSparseLongArray(2);
        if ((mPrivateFlags & PFLAG_FORCE_LAYOUT) == PFLAG_FORCE_LAYOUT ||
                widthMeasureSpec != mOldWidthMeasureSpec ||
                heightMeasureSpec != mOldHeightMeasureSpec) {

            // first clears the measured dimension flag
            mPrivateFlags &= ~PFLAG_MEASURED_DIMENSION_SET;

            resolveRtlPropertiesIfNeeded();
            //判断是否强制测量,如果强制就重新调用onMeasure,整个view树重新测量,否则就从缓存中得到上次的测量规格,
            //因为DecorView是FrameLayout的子类,所以onMeasure就是调用FrameLayout的onMeasure方法
            int cacheIndex = (mPrivateFlags & PFLAG_FORCE_LAYOUT) == PFLAG_FORCE_LAYOUT ? -1 :
                    mMeasureCache.indexOfKey(key);
            if (cacheIndex < 0 || sIgnoreMeasureCache) {
                // measure ourselves, this should set the measured dimension flag back
                onMeasure(widthMeasureSpec, heightMeasureSpec);
                mPrivateFlags3 &= ~PFLAG3_MEASURE_NEEDED_BEFORE_LAYOUT;
            } else {
                long value = mMeasureCache.valueAt(cacheIndex);
                // Casting a long to int drops the high 32 bits, no mask needed
                //调用完这个方法之后,getMeasuredWidth和getMeasuredHeight就可以取到值了
                setMeasuredDimensionRaw((int) (value >> 32), (int) value);
                mPrivateFlags3 |= PFLAG3_MEASURE_NEEDED_BEFORE_LAYOUT;
            }

            // flag not set, setMeasuredDimension() was not invoked, we raise
            // an exception to warn the developer
            if ((mPrivateFlags & PFLAG_MEASURED_DIMENSION_SET) != PFLAG_MEASURED_DIMENSION_SET) {
                throw new IllegalStateException("View with id " + getId() + ": "
                        + getClass().getName() + "#onMeasure() did not set the"
                        + " measured dimension by calling"
                        + " setMeasuredDimension()");
            }

            mPrivateFlags |= PFLAG_LAYOUT_REQUIRED;
        }

        mOldWidthMeasureSpec = widthMeasureSpec;
        mOldHeightMeasureSpec = heightMeasureSpec;
        //在按照固定的格式,把本次的测量规格put到集合中
        mMeasureCache.put(key, ((long) mMeasuredWidth) << 32 |
                (long) mMeasuredHeight & 0xffffffffL); // suppress sign extension
    }

这个方法做的功能大概就是这样,先判断是否有缓存,没缓存就测量一下整个树,然后按照固定的格式在存入缓存中

从这里开始,我们的整个测量过程就开始跑起来了

     protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        int count = getChildCount();
        //只有match_parent和固定宽高 的mode才是EXACTLY,wrap_content是AT_MOST
        final boolean measureMatchParentChildren =
                MeasureSpec.getMode(widthMeasureSpec) != MeasureSpec.EXACTLY ||
                MeasureSpec.getMode(heightMeasureSpec) != MeasureSpec.EXACTLY;
        mMatchParentChildren.clear();

        int maxHeight = 0;  //包含padding的高度
        int maxWidth = 0;   //包含width的宽度
        int childState = 0; //前16位是宽的测量mode,后16位是高的测量mode
        //轮寻测量所有的child
        for (int i = 0; i < count; i++) {
            final View child = getChildAt(i);
            //只要是不为GONE,就会进入测量范围
            if (mMeasureAllChildren || child.getVisibility() != GONE) {
                //测量child的时候,减去padding加上margin的距离,得到child的规格后回调用child的measure,然后在重新走上边分析的流程,调用child的onMeasure
                measureChildWithMargins(child, widthMeasureSpec, 0, heightMeasureSpec, 0);
                //赋值maxWidth和maxHeight,之后就可以用getHeight和getWidth方法了
                final LayoutParams lp = (LayoutParams) child.getLayoutParams();
                maxWidth = Math.max(maxWidth,
                        child.getMeasuredWidth() + lp.leftMargin + lp.rightMargin);
                maxHeight = Math.max(maxHeight,
                        child.getMeasuredHeight() + lp.topMargin + lp.bottomMargin);
                childState = combineMeasuredStates(childState, child.getMeasuredState());
                if (measureMatchParentChildren) {
                    if (lp.width == LayoutParams.MATCH_PARENT ||
                            lp.height == LayoutParams.MATCH_PARENT) {
                        mMatchParentChildren.add(child);
                    }
                }
            }
        }

        // Account for padding too
        maxWidth += getPaddingLeftWithForeground() + getPaddingRightWithForeground();
        maxHeight += getPaddingTopWithForeground() + getPaddingBottomWithForeground();

        // Check against our minimum height and width
        maxHeight = Math.max(maxHeight, getSuggestedMinimumHeight());
        maxWidth = Math.max(maxWidth, getSuggestedMinimumWidth());

        // Check against our foreground's minimum height and width
        final Drawable drawable = getForeground();
        if (drawable != null) {
            maxHeight = Math.max(maxHeight, drawable.getMinimumHeight());
            maxWidth = Math.max(maxWidth, drawable.getMinimumWidth());
        }
        //设置子空间的测量结果
        setMeasuredDimension(resolveSizeAndState(maxWidth, widthMeasureSpec, childState),
                resolveSizeAndState(maxHeight, heightMeasureSpec,
                        childState << MEASURED_HEIGHT_STATE_SHIFT));
        //开始测量宽高都是MATCH_PARENT的布局
        count = mMatchParentChildren.size();
        if (count > 1) {
            for (int i = 0; i < count; i++) {
                final View child = mMatchParentChildren.get(i);
                final MarginLayoutParams lp = (MarginLayoutParams) child.getLayoutParams();

                final int childWidthMeasureSpec;
                if (lp.width == LayoutParams.MATCH_PARENT) {
                    final int width = Math.max(0, getMeasuredWidth()
                            - getPaddingLeftWithForeground() - getPaddingRightWithForeground()
                            - lp.leftMargin - lp.rightMargin);
                    childWidthMeasureSpec = MeasureSpec.makeMeasureSpec(
                            width, MeasureSpec.EXACTLY);
                } else {
                    childWidthMeasureSpec = getChildMeasureSpec(widthMeasureSpec,
                            getPaddingLeftWithForeground() + getPaddingRightWithForeground() +
                            lp.leftMargin + lp.rightMargin,
                            lp.width);
                }

                final int childHeightMeasureSpec;
                if (lp.height == LayoutParams.MATCH_PARENT) {
                    final int height = Math.max(0, getMeasuredHeight()
                            - getPaddingTopWithForeground() - getPaddingBottomWithForeground()
                            - lp.topMargin - lp.bottomMargin);
                    childHeightMeasureSpec = MeasureSpec.makeMeasureSpec(
                            height, MeasureSpec.EXACTLY);
                } else {
                    childHeightMeasureSpec = getChildMeasureSpec(heightMeasureSpec,
                            getPaddingTopWithForeground() + getPaddingBottomWithForeground() +
                            lp.topMargin + lp.bottomMargin,
                            lp.height);
                }

                child.measure(childWidthMeasureSpec, childHeightMeasureSpec);
            }
        }
    }

[Android FrameWork 6.0源码学习] View的重绘过程的更多相关文章

  1. [Android FrameWork 6.0源码学习] View的重绘过程之WindowManager的addView方法

    博客首页:http://www.cnblogs.com/kezhuang/p/关于Activity的contentView的构建过程,我在我的博客中已经分析过了,不了解的可以去看一下<[Andr ...

  2. [Android FrameWork 6.0源码学习] View的重绘过程之Draw

    View绘制的三部曲,测量,布局,绘画现在我们分析绘画部分测量和布局 在前两篇文章中已经分析过了.不了解的可以去我的博客里找一下 下面进入正题,开始分析调用以及函数原理 private void pe ...

  3. [Android FrameWork 6.0源码学习] View的重绘ViewRootImpl的setView方法

    博客首页:http://www.cnblogs.com/kezhuang/p/ 本篇文章来分析一下WindowManager的后续工作,也就是ViewRootImpl的setView函数的工作 /i* ...

  4. [Android FrameWork 6.0源码学习] View的重绘过程之Layout

    View绘制的三部曲,测量,布局,绘画现在我们分析布局部分测量部分在上篇文章中已经分析过了.不了解的可以去我的博客里找一下 View的布局和测量一样,都是从ViewRootImpl中发起,ViewRo ...

  5. [Android FrameWork 6.0源码学习] LayoutInflater 类分析

    LayoutInflater是用来解析XML布局文件,然后生成对象的ViewTree的工具类.是这个工具类的存在,才能让我们写起Layout来那么省劲. 我们接下来进去刨析,看看里边的奥秘 //调用i ...

  6. [Android FrameWork 6.0源码学习] ViewGroup的addView函数分析

    Android中整个的View的组装是采用组合模式. ViewGroup就相当与树根,各种Layout就相当于枝干,各种子View,就相当于树叶. 至于View类.我们就当它是个种子吧.哈哈! Vie ...

  7. [Android FrameWork 6.0源码学习] Window窗口类分析

    了解这一章节,需要先了解LayoutInflater这个工具类,我以前分析过:http://www.cnblogs.com/kezhuang/p/6978783.html Window是Activit ...

  8. 【Spark2.0源码学习】-1.概述

          Spark作为当前主流的分布式计算框架,其高效性.通用性.易用性使其得到广泛的关注,本系列博客不会介绍其原理.安装与使用相关知识,将会从源码角度进行深度分析,理解其背后的设计精髓,以便后续 ...

  9. spark2.0源码学习

    [Spark2.0源码学习]-1.概述 [Spark2.0源码学习]-2.一切从脚本说起 [Spark2.0源码学习]-3.Endpoint模型介绍 [Spark2.0源码学习]-4.Master启动 ...

随机推荐

  1. Samba文件共享服务

    Samba起源: 早期网络想要在不同主机之间共享文件大多要用FTP协议来传输,但FTP协议仅能做到传输文件却不能直接修改对方主机的资料数据,这样确实不太方便,于是便出现了NFS开源文件共享程序:NFS ...

  2. 《Android进阶》之第四篇 ViewPagerIndicator的使用

    1.先将这个开源框架下载到本地: Administrator@QH-20141231RFQJ /d/hixin $ cd ViewPagerIndicator/ Administrator@QH-20 ...

  3. SQLiteDatabase的使用

    新建DBHeler.JAVA package com.hixin.db; import java.util.ArrayList; import java.util.HashMap; import co ...

  4. bzoj 4765 普通计算姬(树状数组 + 分块)

    http://www.lydsy.com/JudgeOnline/problem.php?id=4765 很nice的一道题啊(可能是因为卡了n久终于做出来了 题意就是给你一棵带点权的有根树,sum( ...

  5. 你知道“移动端车牌识别”可以嵌入到PDA中应用吗?

    一.移动端车牌识别产品描述 移动端车牌识别软件是基于移动平台的OCR识别应用程序,支持Android/IOS等多种主流移动操作系统.该产品只需通过智能手机或Pad的摄像头对准车牌,无需拍照,实现自动采 ...

  6. 红包项目总结---MVC版

    起因: 针对传统版的明显缺陷做优化.主要是提升可维护性. 效果  线上:  未发布 线下:http://10.27.5.1/svn/FED/code/hongbao/year-end   hb-fac ...

  7. python——爬虫&问题解决&思考(1)

    最近刚接触python,找点小任务来练练手,希望自己在实践中不断的锻炼自己解决问题的能力.这个小爬虫来自慕课网的一门课程,我在这里记录的是自己学习的过程中遇到的问题和解决方法以及爬虫之外的思考. 这次 ...

  8. 什么是 html 标签,html 实体

    为什么需要转换 更简了,因为有时候我们需要在浏览器页面中显示 html 标签,然而直接输出<script>alert(1)</script>,在浏览页面时将会被当作 html ...

  9. Asp.Net页面传值的方法简单总结【原创】

    1.QueryString 当页面上form按照get的方式向页面发送请求数据的时候,web server会将请求数据放入 一个QEURY_STRING的环境变量中,然后通过QeueryString方 ...

  10. POI使用:用poi接口不区分xls/xlsx格式解析Excel文档(41种日期格式解析方法,5种公式结果类型解析方法,3种常用数值类型精度控制办法)

    一.使用poi解析excel文档 注:全部采用poi接口进行解析,不需要区分xls.xlsx格式,不需要判断文档类型. poi中的日期格式判断仅支持欧美日期习惯,对国内的日期格式并不支持判断,怎么办? ...