首先我們可以看看蘋果官方對(duì)這兩個(gè)方法的解釋：
// return 'best' size to fit given size.
does not actually resize view. Default is return existing view size
- (CGSize)sizeThatFits:(CGSize)size;
// calls sizeThatFits: with current view bounds and changes bounds size.
- (void)sizeToFit;
sizeToFit:會(huì)計(jì)算出最優(yōu)的 size 而且會(huì)改變自己的size
sizeThatFits:會(huì)計(jì)算出最優(yōu)的 size 但是不會(huì)改變 自己的 size
具體看下面的小例子：
sizeToFit
UILabel *label = [[UILabel alloc] initWithFrame:CGRectMake(10, 10, 0, 0)];
[label setBackgroundColor:[UIColor grayColor]];
[label setFont:[UIFont systemFontOfSize:20]];
label.text = @"北京歡飲您！！！";
//sizeToFit:直接改變了這個(gè)label的寬和高，使它根據(jù)上面字符串的大小做合適的改變
[label sizeToFit];
NSLog(@"width=%.1f? height=%.1f ", label.frame.size.width, label.frame.size.height);
[self.view addSubview:label];
輸出結(jié)果：width=163.5 height=24.0
sizeThatFits
UILabel *label = [[UILabel alloc] initWithFrame:CGRectMake(10, 10, 0, 0)];
[label setBackgroundColor:[UIColor grayColor]];
[label setFont:[UIFont systemFontOfSize:20]];
label.text = @"北京歡飲您！！！";
//sizeThatFits并沒有改變?cè)糽abel的大小
CGSize sizeThatFits = [label sizeThatFits:CGSizeZero];
NSLog(@"sizeThatFits: width=%.1f? height=%.1f", sizeThatFits.width, sizeThatFits.height);
NSLog(@"width=%.1f? height=%.1f", label.frame.size.width, label.frame.size.height);
[self.view addSubview:label];
輸出結(jié)果：
2017-03-08 11:34:02.455 joke[2272:116621] sizeThatFits: width=163.5? height=24.0
2017-03-08 11:34:02.455 joke[2272:116621] width=0.0? height=0.0
通過上面的兩個(gè)小例子，我們可以驗(yàn)證出上面的結(jié)論：
sizeToFit:會(huì)計(jì)算出最優(yōu)的 size 而且會(huì)改變自己的size
sizeThatFits:會(huì)計(jì)算出最優(yōu)的 size 但是不會(huì)改變 自己的 size
