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
http://www.cnblogs.com/kezhuang/p/7119859.html