objective-c 中block语法中的传值

                  

    typeof (NSString*) __weak str = @"this is a test";
    double delayInSeconds = 2.0;
    dispatch_time_t popTime = dispatch_time(DISPATCH_TIME_NOW, (int64_t)(delayInSeconds * NSEC_PER_SEC));
    dispatch_after(popTime, dispatch_get_main_queue(), ^(void){
        NSLog(@"%@",str);
    });