13问13答全面学习Android View绘制

//desire的这2个参数就代表屏幕的宽高，
 childwidthmeasurespec = getrootmeasurespec(desiredwindowwidth, lp.width);
 childheightmeasurespec = getrootmeasurespec(desiredwindowheight, lp.height);
 performmeasure(childwidthmeasurespec, childheightmeasurespec);



 //decorview的measurespec就是在这里确定的，其实比普通view的measurespec要简单的多
 //代码就不分析了 一目了然的东西
 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;
} 

//对于普通view的measure来说 是由这个view的 父view ，也就是viewgroup来触发的。
//也就是下面这个measurechildwithmargins方法

protected void measurechildwithmargins(view child,
   int parentwidthmeasurespec, int widthused,
   int parentheightmeasurespec, int heightused) {
   //第一步 先取得子view的 layoutparams 参数值 
  final marginlayoutparams lp = (marginlayoutparams) child.getlayoutparams();

  //然后开始计算子view的spec的值，注意这里看到 计算的时候除了要用子view的 layoutparams参数以外
  //还用到了父view 也就是viewgroup自己的spec的值
  final int childwidthmeasurespec = getchildmeasurespec(parentwidthmeasurespec,
    mpaddingleft + mpaddingright + lp.leftmargin + lp.rightmargin
      + widthused, lp.width);
  final int childheightmeasurespec = getchildmeasurespec(parentheightmeasurespec,
    mpaddingtop + mpaddingbottom + lp.topmargin + lp.bottommargin
      + heightused, lp.height);

  child.measure(childwidthmeasurespec, childheightmeasurespec);
}






//这个算view的spec的方法 看上去一大串 但是真的逻辑非常简单 就是根据父亲viewgroup
//的meaurespec 同时还有view自己的params来确定 view自己的measurespec。
//注意这里的参数是padding,这个值的含义是 父容器已占用的控件的大小 所以view的specsize
//的值 你们可以看到 是要减去这个padding的值的。总大小-已经用的 =可用的。 很好理解。

//然后就是下面的switch逻辑 要自己梳理清楚。其实也不难，主要是下面几条原则
//如果view采用固定宽高，也就是写死的数值那种。那就不管父亲的spec的值了，view的spec 就肯定是exactly 并且大小遵循layout参数里设置的大小。

//如果view的宽高是match_parent ，那么就要看父容器viewgroup的 spec的值了，如果父view的spec是exactly模式，
//那view也肯定是exactly,并且大小就是父容器剩下的空间。如果父容器是at_most模式，那view也是at_most 并且不会超过剩余空间大小

//如果view的宽高是wrap_content, 那就不管父容器的spec了，view的spec一定是at_most 并且不会超过父view 剩余空间的大小。


public static int getchildmeasurespec(int spec, int padding, int childdimension) {
  int specmode = measurespec.getmode(spec);
  int specsize = measurespec.getsize(spec);

  int size = math.max(0, specsize - padding);

  int resultsize = 0;
  int resultmode = 0;

  switch (specmode) {
  // parent has imposed an exact size on us
  case measurespec.exactly:
   if (childdimension >= 0) {
    resultsize = childdimension;
    resultmode = measurespec.exactly;
   } else if (childdimension == layoutparams.match_parent) {
    // child wants to be our size. so be it.
    resultsize = size;
    resultmode = measurespec.exactly;
   } else if (childdimension == layoutparams.wrap_content) {
    // child wants to determine its own size. it can't be
    // bigger than us.
    resultsize = size;
    resultmode = measurespec.at_most;
   }
   break;

  // parent has imposed a maximum size on us
  case measurespec.at_most:
   if (childdimension >= 0) {
    // child wants a specific size... so be it
    resultsize = childdimension;
    resultmode = measurespec.exactly;
   } else if (childdimension == layoutparams.match_parent) {
    // child wants to be our size, but our size is not fixed.
    // constrain child to not be bigger than us.
    resultsize = size;
    resultmode = measurespec.at_most;
   } else if (childdimension == layoutparams.wrap_content) {
    // child wants to determine its own size. it can't be
    // bigger than us.
    resultsize = size;
    resultmode = measurespec.at_most;
   }
   break;

  // parent asked to see how big we want to be
  case measurespec.unspecified:
   if (childdimension >= 0) {
    // child wants a specific size... let him have it
    resultsize = childdimension;
    resultmode = measurespec.exactly;
   } else if (childdimension == layoutparams.match_parent) {
    // child wants to be our size... find out how big it should
    // be
    resultsize = view.susezerounspecifiedmeasurespec ? 0 : size;
    resultmode = measurespec.unspecified;
   } else if (childdimension == layoutparams.wrap_content) {
    // child wants to determine its own size.... find out how
    // big it should be
    resultsize = view.susezerounspecifiedmeasurespec ? 0 : size;
    resultmode = measurespec.unspecified;
   }
   break;
  }
  return measurespec.makemeasurespec(resultsize, resultmode);
 } 

//view的measure是final 方法 我们子类无法修改的。
 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);
  }

  // suppress sign extension for the low bytes
  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();

   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
    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;

  mmeasurecache.put(key, ((long) mmeasuredwidth) << 32 |
    (long) mmeasuredheight & 0xffffffffl); // suppress sign extension
 }

//不过可以看到的是在measure方法里调用了onmeasure方法
//所以就能知道 我们在自定义view的时候一定是重写这个方法！
 protected void onmeasure(int widthmeasurespec, int heightmeasurespec) {
  setmeasureddimension(getdefaultsize(getsuggestedminimumwidth(), widthmeasurespec),
    getdefaultsize(getsuggestedminimumheight(), heightmeasurespec));
 }

//可以看出来这个就是setmeasureddimension方法的调用 这个方法看名字就知道就是确定view的测量宽高的
//所以我们分析的重点就是看这个getdefaultsize 方法 是怎么确定view的测量宽高的
 protected void onmeasure(int widthmeasurespec, int heightmeasurespec) {
  setmeasureddimension(getdefaultsize(getsuggestedminimumwidth(), widthmeasurespec),
    getdefaultsize(getsuggestedminimumheight(), heightmeasurespec));
 }


//这个方法特别简单 基本可以认为就是近似的返回spec中的specsize，除非你的specmode是unspecified
//unspecified 这个一般都是系统内部测量才用的到，这种时候返回size 也就是getsuggestedminimumwidth的返回值
 public static int getdefaultsize(int size, int measurespec) {
  int result = size;
  int specmode = measurespec.getmode(measurespec);
  int specsize = measurespec.getsize(measurespec);

  switch (specmode) {
  case measurespec.unspecified:
   result = size;
   break;
  case measurespec.at_most:
  case measurespec.exactly:
   result = specsize;
   break;
  }
  return result;
}

//跟view的背景相关 这里不多做分析了
protected int getsuggestedminimumwidth() {
  return (mbackground == null) ? mminwidth : max(mminwidth, mbackground.getminimumwidth());
 } 

//重写activity的这个方法
public void onwindowfocuschanged(boolean hasfocus) {
  super.onwindowfocuschanged(hasfocus);
  if (hasfocus) {
   int width = tv.getmeasuredwidth();
   int height = tv.getmeasuredheight();
   log.v("burning", "width==" + width);
   log.v("burning", "height==" + height);

  }
 }

@override
 protected void onstart() {
  super.onstart();
  tv.post(new runnable() {
   @override
   public void run() {
    int width = tv.getmeasuredwidth();
    int height = tv.getmeasuredheight();
   }
  });
 }

@override
 protected void onstart() {
  super.onstart();
  viewtreeobserver observer = tv.getviewtreeobserver();
  observer.addongloballayoutlistener(new viewtreeobserver.ongloballayoutlistener() {
   @override
   public void ongloballayout() {
    int width = tv.getmeasuredwidth();
    int height = tv.getmeasuredheight();
    tv.getviewtreeobserver().removeongloballayoutlistener(this);
   }
  });
 }

/**
  * if this view doesn't do any drawing on its own, set this flag to
  * allow further optimizations. by default, this flag is not set on
  * view, but could be set on some view subclasses such as viewgroup.
  *
  * typically, if you override {@link #ondraw(android.graphics.canvas)}
  * you should clear this flag.
  *
  * @param willnotdraw whether or not this view draw on its own
  */
 public void setwillnotdraw(boolean willnotdraw) {
  setflags(willnotdraw ? will_not_draw : 0, draw_mask);
 }

package com.example.administrator.motioneventtest;

import android.content.context;
import android.graphics.canvas;
import android.graphics.color;
import android.graphics.paint;
import android.util.attributeset;
import android.view.view;

/**
 * created by administrator on 2016/2/4.
 */
public class circleview extends view {

 private int mcolor = color.red;
 private paint mpaint = new paint(paint.anti_alias_flag);

 private void init() {
  mpaint.setcolor(mcolor);
 }

 @override
 protected void onmeasure(int widthmeasurespec, int heightmeasurespec) {
  super.onmeasure(widthmeasurespec, heightmeasurespec);
  int widthspecmode = measurespec.getmode(widthmeasurespec);
  int widthspecsize = measurespec.getsize(widthmeasurespec);
  int heightspecmode = measurespec.getmode(heightmeasurespec);
  int heightspecsize = measurespec.getsize(heightmeasurespec);

  //处理为wrap_content时的情况
  if (widthspecmode == measurespec.at_most && heightspecmode == measurespec.at_most) {
   setmeasureddimension(200, 200);
  } else if (widthspecmode == measurespec.at_most) {
   setmeasureddimension(200, heightspecsize);
  } else if (heightspecmode == measurespec.at_most) {
   setmeasureddimension(widthspecsize, 200);
  }

 }

 @override
 protected void ondraw(canvas canvas) {
  super.ondraw(canvas);
  //处理padding的情况
  final int paddingleft = getpaddingleft();
  final int paddingright = getpaddingright();
  final int paddingtop = getpaddingtop();
  final int paddingbottom = getpaddingbottom();


  int width = getwidth() - paddingleft - paddingright;
  int height = getheight() - paddingtop - paddingbottom;
  int radius = math.min(width, height) / 2;
  canvas.drawcircle(paddingleft + width / 2, paddingtop + height / 2, radius, mpaint);
 }

 public circleview(context context, attributeset attrs, int defstyleattr) {
  super(context, attrs, defstyleattr);
  init();
 }

 public circleview(context context) {
  super(context);
  init();

 }

 public circleview(context context, attributeset attrs) {
  super(context, attrs);
  init();
 }
}

package com.example.administrator.motioneventtest;

import android.content.context;
import android.util.attributeset;
import android.util.log;
import android.view.view;
import android.view.viewgroup;

/**
 * created by administrator on 2016/2/4.
 */
//这里我们只处理了padding的状态 没有处理margin的状态，子view的margin 对measure和layout的影响
//就留给读者自己完成了
public class customhorizontallayout extends viewgroup {

 //设置默认的控件最小是多少 这里不提供自定义属性了 写死在代码里 你们可以自行拓展
 final int minheight = 0;
 final int minwidth = 0;


 public customhorizontallayout(context context) {
  super(context);
 }

 public customhorizontallayout(context context, attributeset attrs) {
  super(context, attrs);
 }

 public customhorizontallayout(context context, attributeset attrs, int defstyleattr) {
  super(context, attrs, defstyleattr);
 }

 @override
 protected void onmeasure(int widthmeasurespec, int heightmeasurespec) {
  super.onmeasure(widthmeasurespec, heightmeasurespec);
  int measurewidth = 0;
  int measureheight = 0;
  final int childcount = getchildcount();
  measurechildren(widthmeasurespec, heightmeasurespec);
  int widthspecmode = measurespec.getmode(widthmeasurespec);
  int widthspecsize = measurespec.getsize(widthmeasurespec);
  int heightspecmode = measurespec.getmode(heightmeasurespec);
  int heightspecsize = measurespec.getsize(heightmeasurespec);
  final view childview = getchildat(0);
  final int paddingleft = getpaddingleft();
  final int paddingright = getpaddingright();
  final int paddingtop = getpaddingtop();
  final int paddingbottom = getpaddingbottom();
  //没有子控件 时 我们的宽高要作特殊处理
  if (childcount == 0) {
   //当没有子控件时，如果长宽有一个为wrap 那么就让这个控件以最小的形式展现
   //这里我们最小设置为0
   if (widthspecmode == measurespec.at_most || heightspecmode == measurespec.at_most) {
    setmeasureddimension(minwidth, minheight);
   } else {
    //否则根据我们的layout属性来
    setmeasureddimension(getlayoutparams().width, getlayoutparams().height);
   }

  } else if (widthspecmode == measurespec.at_most && heightspecmode == measurespec.at_most) {
   measurewidth = childview.getmeasuredwidth() * childcount;
   measureheight = childview.getmeasuredheight();
   setmeasureddimension(paddingleft + measurewidth + paddingright, paddingtop + measureheight + paddingbottom);
  } else if (heightspecmode == measurespec.at_most) {
   measureheight = childview.getmeasuredheight();
   setmeasureddimension(paddingleft + paddingright + widthspecsize, paddingtop + paddingbottom + measureheight);
  } else if (widthspecmode == measurespec.at_most) {
   measurewidth = childview.getmeasuredwidth() * childcount;
   setmeasureddimension(paddingleft + paddingright + measurewidth, paddingtop + paddingbottom + heightspecsize);
  }
 }

 @override
 protected void onlayout(boolean changed, int l, int t, int r, int b) {
  final int paddingleft = getpaddingleft();
  final int paddingright = getpaddingright();
  final int paddingtop = getpaddingtop();
  final int paddingbottom = getpaddingbottom();
  //左边初始位置为0
  int childleft = 0 + paddingleft;
  final int childcount = getchildcount();
  for (int i = 0; i < childcount; i++) {
   final view childview = getchildat(i);
   if (childview.getvisibility() != view.gone) {
    final int childwidth = childview.getmeasuredwidth();
    childview.layout(childleft, 0 + paddingtop, childleft + childwidth, paddingtop + childview.getmeasuredheight());
    childleft += childwidth;
   }
  }
 }
}