iOS 知识小集(5)

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异步方法封装成同步

  • 使用派发组dispatch_group
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- (NSInteger)methodSync {
    NSLog(@"methodSync 开始");
    
    __block NSInteger result = 0;
    
    dispatch_group_t group = dispatch_group_create();
    
    dispatch_group_enter(group);
    
    [self methodAsync:^(NSInteger value) {
    
        result = value;
        
        dispatch_group_leave(group);
        
    }];
    
    dispatch_group_wait(group, DISPATCH_TIME_FOREVER);
    
    NSLog(@"methodSync 结束 result:%ld", (long)result);
    
    return result;
}
  • (推荐)：使用信号量dispatch_semaphore
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- (NSInteger)methodSync {
    NSLog(@"methodSync 开始");
    
    __block NSInteger result = 0;
    
    dispatch_semaphore_t sema = dispatch_semaphore_create(0);
    
    [self methodAsync:^(NSInteger value) {
    
        result = value;
        
        dispatch_semaphore_signal(sema);
        
    }];
   // 这里本来同步方法会立即返回，但信号量=0使得线程阻塞
   // 当异步方法回调之后，发送信号，信号量变为1，这里的阻塞将被解除，从而返回正确的结果
   
    dispatch_semaphore_wait(sema, DISPATCH_TIME_FOREVER);
    
    NSLog(@"methodSync 结束 result:%ld", (long)result);
    
    return result;
}