Android(安卓)onMeasure(widthSpec, heightSpec)

每个View中都有一个测量绘制控件大小的方法onMeasure(int widthMeasureSpec, int heightMeasureSpec) ，该方法用于初始化控件所占的区域：

摘自SlidingDrawer.java，仅作参考说明onMeasure(int widthMeasureSpec, int heightMeasureSpec)方法

@Override    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {        //onMeasure方法传入的两个参数widthMeasureSpec, heightMeasureSpec，其单位为dp或dip            int widthSpecMode = MeasureSpec.getMode(widthMeasureSpec);    //这里判断单位是dp或dip，有或者其他的单位类型        int widthSpecSize =  MeasureSpec.getSize(widthMeasureSpec); //将单位转为px        int heightSpecMode = MeasureSpec.getMode(heightMeasureSpec);        int heightSpecSize =  MeasureSpec.getSize(heightMeasureSpec);        if (widthSpecMode == MeasureSpec.UNSPECIFIED || heightSpecMode == MeasureSpec.UNSPECIFIED) {            throw new RuntimeException("SlidingDrawer cannot have UNSPECIFIED dimensions");        }        //        final View handle = mHandle;        measureChild(handle, widthMeasureSpec, heightMeasureSpec);        if (mVertical) {            int height = heightSpecSize - handle.getMeasuredHeight() - mTopOffset;            mContent.measure(MeasureSpec.makeMeasureSpec(widthSpecSize, MeasureSpec.EXACTLY),                    MeasureSpec.makeMeasureSpec(height, MeasureSpec.EXACTLY));        } else {            int width = widthSpecSize - handle.getMeasuredWidth() - mTopOffset;            mContent.measure(MeasureSpec.makeMeasureSpec(width, MeasureSpec.EXACTLY),                    MeasureSpec.makeMeasureSpec(heightSpecSize, MeasureSpec.EXACTLY));        }        //最后绘制父控件的大小        setMeasuredDimension(widthSpecSize, heightSpecSize);        //super.onMeasure(widthMeasureSpec, heightMeasureSpec)原型则是下面这样写的:        //setMeasuredDimension(getDefaultSize(getSuggestedMinimumWidth(), widthMeasureSpec),        //        getDefaultSize(getSuggestedMinimumHeight(), heightMeasureSpec));    }

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