frame 和bounds

CGRect bounds = [[UIScreen mainScreen] bounds];
    //bounds是uiview自身的坐标，frame是父uiview的坐标，center是uiview中心在父uiview（superview）的坐标
    int screenWidth =  bounds.size.width;
    int screenHeight =  bounds.size.height;
   
    CGRect frame = CGRectMake((screenWidth-312)/2, (screenHeight-312)/2, 312, 312);//从第一个到第四个分别是: x坐标,y坐标,宽度width,高度height;CGRectMake的参考点是左上角