iOS的layout机制相关方法

- (CGSize)sizeThatFits:(CGSize)size {
    return CGSizeMake(, );
    //Asks the view to calculate 
    //and return the size that best fits the specified size.
}
//sizeToFit会自动调用sizeThatFits方法；
- (void)sizeToFit {
    //You should not override this method.
    //If you want to change the default sizing information for your view,
    //override the sizeThatFits: instead.   
}

//1.init初始化不会触发layoutSubviews
//2.用initWithFrame 进行初始化时(rect不能为0)或者改变frame会触发
//3.addSubview会触发
//4.滚动ScrollView也会触发
//5.旋转Screen会触发superView上的layoutSubviews事件
//6.改变一个View的大小的时候也会触发superView上的layoutSubviews事件
- (void)layoutSubviews {
//Lays out subviews.

//You should override this method only if the autoresizing and constraint-based behaviors of the subviews do not offer the behavior you want.

// You can use your implementation to set the frame rectangles of your subviews directly.

//You should not call this method directly. 

//If you want to force a layout update, call the setNeedsLayout method instead to do so prior to the next drawing update. 

//If you want to update the layout of your views immediately, call the layoutIfNeeded method.


}

- (void)layoutIfNeeded {
//Lays out the subviews immediately.
//Use this method to force the layout of subviews before drawing.
}

- (void)setNeedsLayout {

}

- (void)setNeedsDisplay {
//You can use this method or the setNeedsDisplayInRect: 
//to notify the system that your view’s contents need to be redrawn
}

- (void)setNeedsDisplayInRect:(CGRect)rect {
}

- (void)drawRect:(CGRect)rect {
//Only override drawRect:
//if you perform custom drawing.  
}

- (void)viewWillLayoutSubviews {
//Called to notify the view controller that its view is about to layout its subviews.
}

- (void)viewDidLayoutSubviews {
//Your view controller can override this method to make changes 
//after the view lays out its subviews.   
}