sizeThatFits and sizeToFit是UIView的两个方法

 1   
 2 - (CGSize)sizeThatFits:(CGSize)size;       
 3 作用：return ‘best‘ size to fit given size. does not actually resize view. Default is return existing view size  
 4 - (void)sizeToFit;       
 5 作用： calls sizeThatFits: with current view bounds and changes bounds size.  
 6   
 7 - (void)viewDidLoad  
 8 {  
 9     [super viewDidLoad];  
10     UIView *view = [[UIView alloc] initWithFrame:CGRectMake(100, 100, 200, 100)];  
11     view.backgroundColor = [UIColor yellowColor];  
12     UILabel *label = [[UILabel alloc] initWithFrame:CGRectMake(5, 5, 0, 0)];  
13     [label setFont:[UIFont systemFontOfSize:20]];  
14     label.text = @"hello wdszgrf";  
15     CGSize sizeThatFits = [label sizeThatFits:CGSizeZero];  
16     NSLog(@"---- %f  %f ----", sizeThatFits.width, sizeThatFits.height);     
17     // output:  ---- 117.000000  24.000000 ----  
18   
19     NSLog(@"**** %f  %f ****", label.frame.size.width, label.frame.size.height);     
20     // output:  **** 0.000000  0.000000 **** 说明sizeThatSize并没有改变原始label的大小  
21    
22     [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  
23     [label setCenter:CGPointMake(80, 50)];  
24     NSLog(@"==== %f %f ====", label.frame.size.width, label.frame.size.height);       
25     // output:   ==== 117.000000 24.000000 ====   
26   
27     [view addSubview:label];  
28     [self.view addSubview:view];  
29 }