IOS中label的文字一个个动态出现

程序很简单，关键是涉及多线程问题以及线程休眠问题

下面看下代码：

#import "ViewController.h"

@interface ViewController ()

{

    UILabel *_label;

    NSString *_str;

}

@end

@implementation ViewController

- (void)viewDidLoad {

    [super viewDidLoad];

   

    self.view.backgroundColor = [UIColor whiteColor];

    _label = [[UILabel alloc] initWithFrame:CGRectMake(50, 200, 375-100, 300)];

    _label.numberOfLines = 0;

    _label.font = [UIFont systemFontOfSize:16];

    _label.backgroundColor = [UIColor purpleColor];

    _label.textColor = [UIColor blackColor];

    [self.view addSubview:_label];

    //开启线程

    NSThread *thread = [[NSThread alloc]initWithTarget:self selector:@selector(animationLabel) object:nil];

    [thread start];

    //初始化字符串，为我们最后显示内容

    _str = @"感谢对本文的收看，希望能帮到你";

    

}

//线程的代码体，执行休眠

-(void)animationLabel

{

    for (int i=0; i<_str.length; i++) {

        //每次给Label显示的文字是从最前边到i+1个

        [self performSelectorOnMainThread:@selector(refreshUI:) withObject:[_str substringWithRange:NSMakeRange(0, i+1)]  waitUntilDone:YES];

        [NSThread sleepForTimeInterval:0.3];

    }

    

}

//执行主线程修改UI

-(void)refreshUI:(NSString *)contentStr

{

    _label.text = contentStr;

}

@end