ViewTree:组合模式

View {ViewParent mParent;
}
ViewGroup extends View implements ViewParent{View[] mChildren;
}

   树状结构传递各种事件

        measure事件

        layout事件

        draw事件

        TouchEvent事件

  

measure事件的传递

        View的measure和onMeasure

class View {void measure(int widthMeasureSpec, int heightMeasureSpec) {onMeasure(widthMeasureSpec, heightMeasureSpec);}void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {//设置控件的宽高setMeasuredDimension(getDefaultSize(getSuggestedMinimumWidth(), widthMeasureSpec),getDefaultSize(getSuggestedMinimumHeight(), heightMeasureSpec));}}class ViewGroup {//没有重写measure()和onMeasure()方法
}

        View.MeasureSpec

                封装size和mode

                mode包含 UNSPECIFIED、EXACTLY、AT_MOST、

                        UNSPECIFIED

                                父控件不会对子控件进行限制

                        EXACTLY

                                父控件对子控件进行精确尺寸设置：忽视子控件本身的设置

                        AT_MOST

                                父控件对子控件给出上限尺寸        

                API

                        MeasureSpec.getMode(measureSpec)

                        MeasureSpec.getSize(measureSpec)

                        MeasureSpec.makeMeasureSpec(size, mode)

        布局控件重写onMeasure方法

                重写onMeasure方法完成2个任务

                       1.向子控件传递measure事件

                       2.设置布局控件本身的宽高

                                View.setMeasuredDimension(width, height)方法用于设置控件的宽高

                LinearLayout重写onMeasure方法

                     根据属性orientation，选择measureVertical或measureHorizontal

                     步骤

                                1.第一次遍历，记录totalWeight和totalLength

                                        totalLength是累计子控件的宽或高