场景
一个 LinearLayout 垂直方向上包含两个 TextView 和一个 RelativeLayout
RelativeLayout 又包含两个TextView
根据这个场景,分析一下 LinearLayout 的 measureVertical()做了哪些事情
如下图:
xml:
代码语言：txt复制<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">
<TextView
android:layout_width="match_parent"
android:layout_height="100dp"
android:background="@android:color/holo_orange_dark"
android:gravity="center"
android:text="TextView1"
android:textColor="@android:color/white"
android:textSize="24sp" />
<TextView
android:layout_width="match_parent"
android:layout_height="150dp"
android:background="@android:color/holo_green_light"
android:gravity="center"
android:text="TextView2"
android:textColor="@android:color/white"
android:textSize="24sp" />
<RelativeLayout
android:layout_width="match_parent"
android:layout_height="100dp"
android:background="@android:color/holo_orange_light">
<TextView
android:layout_width="wrap_content"
android:layout_height="100dp"
android:layout_alignParentLeft="true"
android:gravity="center"
android:text="TextView"
android:textColor="@android:color/white"
android:textSize="24sp" />
<TextView
android:layout_width="wrap_content"
android:layout_height="100dp"
android:layout_alignParentRight="true"
android:gravity="center"
android:text="TextView"
android:textColor="@android:color/white"
android:textSize="24sp" />
</RelativeLayout>
</LinearLayout>上面是 xml 中的定义
onMeasure()
1.垂直方向上获取同一层级的 view 的数量
2.计算高度
3.计算宽度
依次如下:
1. 垂直方向上获取同一层级的 view 的数量
垂直方向上获取 child 的个数,当前是 3 个,虽然RelativeLayout 也包含两个TextView
但是不是同一级的.
代码语言：txt复制void measureVertical(int widthMeasureSpec, int heightMeasureSpec) {
//
final int count = getVirtualChildCount();
}2. 计算高度
大体流程如下:
2.1 用for 循环所有的child 控件,分别计算出每个 child高度和 child 的 margin, 累加记为mTotalLength
2.2 mTotalLength 加上 padding,记为heightSize
2.3 如设置背景heightSize和背景比较一下高度取大值,记为heightSize
2.4 heightSize 和父类传入的 heightMeasureSpec参数 比较得出最终LinearLayout的高度.
代码语言：txt复制 void measureVertical(int widthMeasureSpec, int heightMeasureSpec) {
for (int i = 0; i < count; i) {
final View child = getVirtualChildAt(i);
final LayoutParams lp = (LayoutParams) child.getLayoutParams();
final boolean useExcessSpace = lp.height == 0 && lp.weight > 0;
if (heightMode == MeasureSpec.EXACTLY && useExcessSpace) {
//...
} else {
// 计算当前 index 对应的 child 的childHeight
final int childHeight = child.getMeasuredHeight();
// mTotalLength加上margin,
mTotalLength = Math.max(totalLength, totalLength childHeight lp.topMargin
lp.bottomMargin getNextLocationOffset(child));
}
}
//mTotalLength 加上padding
mTotalLength = mPaddingTop mPaddingBottom;
// heightSize 作为计算的高度
int heightSize = mTotalLength;
//若设置背景的话heightSize 和背景比较一下取大值,
heightSize = Math.max(heightSize, getSuggestedMinimumHeight());
//结合父类传入的heightMeasureSpec计算最终的高度
int heightSizeAndState = resolveSizeAndState(heightSize, heightMeasureSpec, 0);
}3. 计算宽度
计算宽度的过程和高度差不多,这里不再重复,下方源码也有注释,可以对着参考.
最终调用方法
setMeasuredDimension(resolveSizeAndState(maxWidth, widthMeasureSpec, childState),heightSizeAndState);
结束onMeasure()流程
源码:
代码语言：txt复制public class LinearLayout extends ViewGroup {
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
if (mOrientation == VERTICAL) {
// 分析这个
measureVertical(widthMeasureSpec, heightMeasureSpec);
} else {
measureHorizontal(widthMeasureSpec, heightMeasureSpec);
}
}
void measureVertical(int widthMeasureSpec, int heightMeasureSpec) {
mTotalLength = 0;
int maxWidth = 0;
int childState = 0;
int alternativeMaxWidth = 0;
boolean allFillParent = true;
final int count = getVirtualChildCount();
final int widthMode = MeasureSpec.getMode(widthMeasureSpec);
final int heightMode = MeasureSpec.getMode(heightMeasureSpec);
for (int i = 0; i < count; i) {
final View child = getVirtualChildAt(i);
final LayoutParams lp = (LayoutParams) child.getLayoutParams();
final boolean useExcessSpace = lp.height == 0 && lp.weight > 0;
if (heightMode == MeasureSpec.EXACTLY && useExcessSpace) {
//...
} else {
//没有设置totalWeight =0, 因此mTotalLength =0
final int usedHeight = totalWeight == 0 ? mTotalLength : 0;
//测量一下child
measureChildBeforeLayout(child, i, widthMeasureSpec, 0,
heightMeasureSpec, usedHeight);
// 上面测量了 因此这个可以拿到当前 index 的 child 的childHeight
final int childHeight = child.getMeasuredHeight();
final int totalLength = mTotalLength;
// 测量第一个 child 时候,mTotalLength为 :第一个child 的childHeight
mTotalLength = Math.max(totalLength, totalLength childHeight lp.topMargin
lp.bottomMargin getNextLocationOffset(child));
}
boolean matchWidthLocally = false;
final int margin = lp.leftMargin lp.rightMargin;
// 测量的宽度= child 的测量宽度 margin
final int measuredWidth = child.getMeasuredWidth() margin;
//maxWidth 初始值是 0, maxWidth和measuredWidth比较取大的
maxWidth = Math.max(maxWidth, measuredWidth);
childState = combineMeasuredStates(childState, child.getMeasuredState());
allFillParent = allFillParent && lp.width == LayoutParams.MATCH_PARENT;
if (lp.weight > 0) {
//...
} else {
// 结果和matchWidthLocally有关系,matchWidthLocally默认为 false 和上面有关系
alternativeMaxWidth = Math.max(alternativeMaxWidth,
matchWidthLocally ? margin : measuredWidth);
}
i = getChildrenSkipCount(child, i);
}
// 至此上面的 for 循环结束
//mTotalLength 为 child 的childHeight之和
// 总高度 在这加上 padding ,没有设置padding 都是 0, mTotalLength不变
mTotalLength = mPaddingTop mPaddingBottom;
// mTotalLength 赋值给
int heightSize = mTotalLength;
//没有背景为heightSize
//getSuggestedMinimumHeight() 是跟设置背景有关,getSuggestedMinimumHeight()无背景=0
heightSize = Math.max(heightSize, getSuggestedMinimumHeight());
//结合heightMeasureSpec调整计算大小
//但是 heightMeasureSpec 是 match_parent 因此大小为match_parent 屏幕的高
int heightSizeAndState = resolveSizeAndState(heightSize, heightMeasureSpec, 0);
heightSize = heightSizeAndState & MEASURED_SIZE_MASK;
//heightSize 是屏幕高度
//之差就是 剩余的空间
int remainingExcess = heightSize - mTotalLength
(mAllowInconsistentMeasurement ? 0 : consumedExcessSpace);
//totalWeight 是 0
if (skippedMeasure || remainingExcess != 0 && totalWeight > 0.0f) {
//...
} else {
// 计算宽度
alternativeMaxWidth = Math.max(alternativeMaxWidth,
weightedMaxWidth);
}
// padding 都是 0
maxWidth = mPaddingLeft mPaddingRight;
// 和getSuggestedMinimumWidth()比较,也是和背景有关
maxWidth = Math.max(maxWidth, getSuggestedMinimumWidth());
setMeasuredDimension(resolveSizeAndState(maxWidth, widthMeasureSpec, childState),
heightSizeAndState);
}
}onLayout()
1.垂直方向上获取同一层级的 view 的数量
2.计算初始摆放的位置
3.依次摆放子view 的位置
依次如下:
1. 垂直方向上获取同一层级的子 view 的数量
代码语言：txt复制 final int count = getVirtualChildCount();2. 计算初始摆放的位置
代码语言：txt复制 childTop = mPaddingTop;
//...
childTop = lp.topMargin;3. 一次摆放子 view 的位置
setChildFrame()方法确定子 view 的位置
代码语言：txt复制setChildFrame()
//
child.layout(left, top, left width, top height);子view 是 TextView,是 view,会直接调用 setFrame()方法确定 view 的位置,将位置信息保存成员变量
子view 是 RelativeLayout,是 ViewGroup,layout()到onLayout()方法再次递归,最终确定所有view 的位置
onLayout() 部分源码如下:
代码语言：txt复制public class LinearLayout extends ViewGroup {
@Override
protected void onLayout(boolean changed, int l, int t, int r, int b) {
if (mOrientation == VERTICAL) {
//分析这个
layoutVertical(l, t, r, b);
} else {
layoutHorizontal(l, t, r, b);
}
}
void layoutVertical(int left, int top, int right, int bottom) {
final int paddingLeft = mPaddingLeft;
int childTop;
int childLeft;
// 获取宽度
final int width = right - left;
int childRight = width - mPaddingRight;
int childSpace = width - paddingLeft - mPaddingRight;
//获取 child 数量
final int count = getVirtualChildCount();
final int majorGravity = mGravity & Gravity.VERTICAL_GRAVITY_MASK;
final int minorGravity = mGravity & Gravity.RELATIVE_HORIZONTAL_GRAVITY_MASK;
// 根据mGravity 计算childTop
switch (majorGravity) {
//...
default:
childTop = mPaddingTop;
break;
}
for (int i = 0; i < count; i ) {
final View child = getVirtualChildAt(i);
if (child == null) {
//...
} else if (child.getVisibility() != GONE) {
// 获取当前 index 的 child 的 宽度
final int childWidth = child.getMeasuredWidth();
final int childHeight = child.getMeasuredHeight();
final LinearLayout.LayoutParams lp =
(LinearLayout.LayoutParams) child.getLayoutParams();
// 获取gravity
int gravity = lp.gravity;
if (gravity < 0) {
gravity = minorGravity;
}
//
final int absoluteGravity = Gravity.getAbsoluteGravity(gravity, layoutDirection);
switch (absoluteGravity & Gravity.HORIZONTAL_GRAVITY_MASK) {
//...
default:
childLeft = paddingLeft lp.leftMargin;
break;
}
childTop = lp.topMargin;
//child.layout()方法
// child 是 TextView这里layout()方法进入 View 的layout()方法,会回调onLayoutChange()方法
// View 的layout()方法 内部调用onLayout()方法,最终执行 TextView的onLayout()
setChildFrame(child, childLeft, childTop getLocationOffset(child),
childWidth, childHeight);
childTop = childHeight lp.bottomMargin getNextLocationOffset(child);
i = getChildrenSkipCount(child, i);
}
}
}
private void setChildFrame(View child, int left, int top, int width, int height) {
child.layout(left, top, left width, top height);
}
}至此,LinearLayout 简单的加载这三个垂直控件的流程分析完毕
至于带 weight 属性的情况,我们后面分析.
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