一、 从ActivityThread到View绘制流程图，如下
UI的具体绘制流程.jpg
二、 Activity oncreate setContent加载xml布局过程
1.Activity.class --> setContentView
2.PhoneWindow.class --> setContentView -->installDecor() 476行
- PhoneWindow.class -->generateDecor 2338行
4.PhoneWindow.class -->generateLayout 2359行
5.PhoneWindow.class -->mDecor.onResourcesLoaded 2630行
最外层DecorView，然后添加根布局screen_simple.xml, 返回@android:id/content 根布局
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:fitsSystemWindows="true"
android:orientation="vertical">
<ViewStub android:id="@+id/action_mode_bar_stub"
android:inflatedId="@+id/action_mode_bar"
android:layout="@layout/action_mode_bar"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:theme="?attr/actionBarTheme" />
<FrameLayout
android:id="@android:id/content"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:foregroundInsidePadding="false"
android:foregroundGravity="fill_horizontal|top"
android:foreground="?android:attr/windowContentOverlay" />
</LinearLayout>
6.初始化完父容器mContentParent，在PhoneWindow setContent()里mLayoutInflater.inflate(layoutResID, mContentParent);
加载解析xml布局,然后添加到mContentParent里。
7.LayoutInflater.class -->inflate
三、 Activity UI开始绘制是在onResume,并不是onCreate时
- ActivityTread --> handleResumeActivity 4468行
- handleResumeActivity --> wm.addView(decor, l); 4535行
3.WindowManagerImpl --> addView 107行
4.WindowManagerGlobal --> addView 331行 - addView --> root.setView(view, wparams, panelParentView, userId); 409行
6.ViewRootImpl --> setView 919行 - ViewRootImpl --> requestLayout 1604行
- ViewRootImpl --> scheduleTraversals 1923行
- ViewRootImpl --> doTraversal 1943行
- ViewRootImpl --> performTraversals 2332行
- performTraversals --> performMeasure 2906行 --> mView.measure(childWidthMeasureSpec, childHeightMeasureSpec) --> onMeasure();
- performTraversals --> performLayout 2938行 --> host.layout(0, 0, host.getMeasuredWidth(), host.getMeasuredHeight()) --> onLayout();
- performTraversals --> performDraw 3099行 --> onDraw();
四、 View测量measure
1.在学习view测量之前，我们先了解下MeasureSpec对象, 通过MeasureSpec.getMode()可获取测量模式， MeasureSpec.getSize()可获取测量大小
2.MeasureSpec的三种测量模式
image.png
3.为了深入了解，接下来我们讲解下MeasureSpec是 如何运算
Java中定义MeasureSpec 是一个int类型，4个字节 4x8 =32位，前两位为MeasureSpec的Mode类型，后面30放置MeasureSpec的size大小
我们以MeasureSpec Mode = AT_MOST, MeasureSpec size = 1080为例
public static final int AT_MOST = 2 << MODE_SHIFT
private static final int MODE_SHIFT = 30;
private static final int MODE_MASK = 0x3 << MODE_SHIFT
AT_MOST值为2，十进制2转成二进制 为10, 然后左移MODE_SHIFT 30位
结果为 10 0000000000 0000000000 0000000000
MeasureSpec size 是1080,转成二进制10000111000,补全32位得到结果
00 0000000000 0000000001 0000111000
int MeasureSpec = makeMeasureSpec(size, mode);
public static int makeMeasureSpec(@IntRange(from = 0, to = (1 << MeasureSpec.MODE_SHIFT) - 1) int size,
@MeasureSpecMode int mode) {
if (sUseBrokenMakeMeasureSpec) {
return size + mode;
} else {
return (size & ~MODE_MASK) | (mode & MODE_MASK);
}
}
MODE_MASK = 11 0000000000 0000000000 0000000000
~MODE_MASK =00 1111111111 1111111111 1111111111
size & ~MODE_MASK
00 0000000000 0000000001 0000111000 &
00 1111111111 1111111111 1111111111
=
00 0000000000 0000000001 0000111000
mode & MODE_MASK
10 0000000000 0000000000 0000000000 &
11 0000000000 0000000000 0000000000
=
10 0000000000 0000000000 0000000000
(size & ~MODE_MASK) | (mode & MODE_MASK)
00 0000000000 0000000001 0000111000 |
10 0000000000 0000000000 0000000000
=
10 0000000000 0000000001 0000111000
int MeasureSpec = makeMeasureSpec(1080, MeasureSpec.AT_MOST) =
10 0000000000 0000000001 0000111000
java二进制运算符
image.png
4.View测量onMeasure，不同view测量规则不一样，我们以FrameLayout为例
FrameLayout是帧布局，他的子view是一个个重叠放置，所以它的大小取解于最大子View的大小maxHeight,maxWidth
int maxHeight = 0;
int maxWidth = 0;
int childState = 0;
for (int i = 0; i < count; i++) {
final View child = getChildAt(i);
if (mMeasureAllChildren || child.getVisibility() != GONE) {
measureChildWithMargins(child, widthMeasureSpec, 0, heightMeasureSpec, 0);
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);
}
}
}
}
measureChildWithMargins测量出子view大小-->getChildMeasureSpec
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;
}
//noinspection ResourceType
return MeasureSpec.makeMeasureSpec(resultSize, resultMode);
}
如果父类mode是EXACTLY精确
1.如果子类childDimension>0,则子类大小resultSize = childDimension，并且类型是精确
2.如果子类childDimension为LayoutParams.MATCH_PARENT，则子类大小resultSize=父类大小size，并且类型是精确
3.如果子类childDimension为LayoutParams.WRAP_CONTENT，则子类大小resultSize最大为父类大小size,类型是At_MOST
后面几种类型依此类推，不再详解
五、 View测量onLayout
我们还是以简单的FrameLayout为例
1.布局子view
image.png
childView左起点childLeft = parentLeft + lp.leftMargin childRight=childLeft+width
childView顶部起点childTop = parentTop + lp.topMargin childBottom= childTop +height
image.png
六、 View测量onDraw
public void draw(Canvas canvas) {
final int privateFlags = mPrivateFlags;
mPrivateFlags = (privateFlags & ~PFLAG_DIRTY_MASK) | PFLAG_DRAWN;
/*
* Draw traversal performs several drawing steps which must be executed
* in the appropriate order:
*
* 1. Draw the background
* 2. If necessary, save the canvas' layers to prepare for fading
* 3. Draw view's content
* 4. Draw children
* 5. If necessary, draw the fading edges and restore layers
* 6. Draw decorations (scrollbars for instance)
* 7. If necessary, draw the default focus highlight
*/
// Step 1, draw the background, if needed
int saveCount;
drawBackground(canvas);
// skip step 2 & 5 if possible (common case)
final int viewFlags = mViewFlags;
boolean horizontalEdges = (viewFlags & FADING_EDGE_HORIZONTAL) != 0;
boolean verticalEdges = (viewFlags & FADING_EDGE_VERTICAL) != 0;
if (!verticalEdges && !horizontalEdges) {
// Step 3, draw the content
onDraw(canvas);
// Step 4, draw the children
dispatchDraw(canvas);
drawAutofilledHighlight(canvas);
// Overlay is part of the content and draws beneath Foreground
if (mOverlay != null && !mOverlay.isEmpty()) {
mOverlay.getOverlayView().dispatchDraw(canvas);
}
// Step 6, draw decorations (foreground, scrollbars)
onDrawForeground(canvas);
// Step 7, draw the default focus highlight
drawDefaultFocusHighlight(canvas);
if (isShowingLayoutBounds()) {
debugDrawFocus(canvas);
}
// we're done...
return;
}
① 绘制 View 的背景
② 绘制 View 的内容
③ 绘制子 View
④ 绘制装饰（渐变框、滑动条、前景等)
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