IOS block定义与使用

Block经常用到也非常实用，下面是他的定义与使用。

定义

• .h文件

    typedefvoid (^CompletionBlock)(UIImage *image);   -(void)takeScreenshot:(CompletionBlock)block;
  

• .M文件

    - (void)takeScreenshot:(CompletionBlock)block
    {
    		dispatch_queue_t queue = dispatch_queue_create("screenshot", 0);
    		dispatch_async(queue, ^(void) {
  
    	UIGraphicsBeginImageContextWithOptions(self.frame.size, NO, 0.0);
    	[self.layerrenderInContext:UIGraphicsGetCurrentContext()];
  
    	UIImage *screenshot = UIGraphicsGetImageFromCurrentImageContext();
    	UIGraphicsEndImageContext();
  
    	dispatch_async(dispatch_get_main_queue(), ^{
        block(screenshot);
    	});
    	dispatch_release(queue);
    		});
    }
  

• 引用文件

    [self takeScreenshot:^(UIImage *image) {
    //do something...
    	}];