sizeThatFits 和 sizeToFit区别

- (void)viewDidLoad
{
[super viewDidLoad];
UIView *view = [[UIView alloc] initWithFrame:CGRectMake(100, 100, 200, 100)];
view.backgroundColor = [UIColor yellowColor];
UILabel *label = [[UILabel alloc] initWithFrame:CGRectMake(5, 5, 0, 0)];
[label setFont:[UIFont systemFontOfSize:20]];
label.text = @"hello wdszgrf";
CGSize sizeThatFits = [label sizeThatFits:CGSizeZero];
NSLog(@"---- %f  %f ----", sizeThatFits.width, sizeThatFits.height);
// output:  ---- 117.000000  24.000000 ----

NSLog(@"**** %f  %f ****", label.frame.size.width, label.frame.size.height);
// output:  **** 0.000000  0.000000 **** 说明sizeThatSize并没有改变原始label的大小

[label sizeToFit];  // 这样搞就直接改变了这个label的宽和高，使它根据上面字符串的大小做合适的改变
[label setCenter:CGPointMake(80, 50)];
NSLog(@"==== %f %f ====", label.frame.size.width, label.frame.size.height);
// output:   ==== 117.000000 24.000000 ====

[view addSubview:label];
[self.view addSubview:view];
}

sizeThatFits不会改变控件原始尺寸

sizeToFit会改变控件原始尺寸