1 //定義了一個block類型MyBlock，MyBlock類型的變量只能指向帶兩個int的參數(shù)和返回int的代碼塊  2 typedef int (^MyBlock)(int,int);  3 //定義一個函數(shù)指針  4 int (*pMath)(int ,int);  5  6 int add(int a,int b)  7 {  8     return a+b;  9 }10 11 int sub(int a,int b) 12 { 13     return a-b; 14 }15 16 int main(int argc, const char * argv[]) { 17     @autoreleasepool { 18         pMath = add;//指向函數(shù)指針 19         //NSLog(@"sum: %d",pMath(2,3)); 20         pMath = sub; 21 22         //定義了一個block，block只能指向帶2個int的參數(shù)，返回int的代碼塊  23         //以^開始的為代碼塊,后面（）是參數(shù)，然后{}代碼塊 24         int (^bloke1)(int,int) = ^(int a,int b){ 25             return a+b; 26         };27 28         int s = bloke1(3,5); 29         NSLog(@"s:%d",s);  30         //定義一個block指向沒有參數(shù)沒有返回值的代碼塊（沒有參數(shù)，void可以省略） 31         void (^block2)(void) = ^{ 32             NSLog(@"PRograming is fun!"); 33         }; 34         block2(); 35         int (^block3)(int,int) = ^(int a,int b ){ 36             return a-b; 37 38         }; 39 40         //定義了MyBlock類型的變量，賦值代碼塊 41         MyBlock block4 = ^(int a,int b){ 42             return a*b; 43         };44 45         NSLog(@"%d",block4(2,5)); 46 47         int c = 10; 48         __block int d = 1; 49         //block塊可以訪問塊外的變量但是不能修改，如果需要修改，變量前加上__block修飾 50         void (^block5)(void) = ^{ 51             d = d+2; 52             NSLog(@"c:%d,d:%d",c,d); 53         }; 54         block5(); 55     } 56     return 0; 57 }

3）解決Block互為強引用時的警告的方法 例如：

1  UIImageView *imgv = [[UIImageView alloc]initWithFrame:CGRectMake(10, 50, 300, 150)];2     [self.view addSubview:imgv];3     4 //使用 __unsafe_unretained 重新定義對象 解決互為強引用的問題5  __unsafe_unretained UIImageView *weakImagev = imgv;6     [imgv setImageWithURL:[NSURL URLWithString:@"http://xxx/xxx.jpg?570x300_120"] withPlaceHolder:nil 7                 competion:^(UIImage *image) {8                     weakImagev.image = image;9 }];

4）有返回值的Block的使用方法 實例代碼： 

//將局部變量聲明為__block，表示將會由block進行操作，比如：   __block float price = 1.99; float (^finalPrice)(int) = ^(int quantity){  return quantity * price;};int orderQuantity = 10;price =0.99;NSLog(@"With block storage modifier - Ordering %d units, final price is: $%2.2f", orderQuantity, finalPrice(orderQuantity)); //此時輸出為With block storage modifier – Ordering 10 units, final price is: $9.90