Android View绘制 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;
   }
  }
 }
}