学会使用Block编程

1.Block是什么？

Block是一个C级别的语法以及运行时的一个特性，和标准C中的函数（函数指针）类似，可以看成一个语句块或者更多时候看成一个匿名函数。

+ (void)animateWithDuration:(NSTimeInterval)duration animations:(void (^)(void))animations NS_AVAILABLE_IOS(4_0);

[ UIView animateWithDuration:10 animations:^{
       NSLog(@"%@,",@"block");
    }]; 

2.Block在什么情况下使用？

Block除了能够定义参数列表、返回类型外，还能够获取被定义时的词法范围内的状态（比如局部变量），并且在一定条件下（比如使用__block变量）能够修改这些状态。此外，这些可修改的状态在相同词法范围内的多个block之间是共享的，即便出了该词法范围（比如栈展开，出了作用域），仍可以继续共享或者修改这些状态。通常来说，block都是一些简短代码片段的封装，适用作工作单元，通常用来做并发任务、遍历、以及回调。

3.Block如何申明？（对比于c语言中的函数申明）

4.如何调用Block?(类比于函数指针)

 int (*CFunc) (int a) //函数调用
 int result = CFunc(10);
 int (^BFunc) (int  a)  //Block调用
 int result = BFunc(10);

5.Block编程实例（实现回调）

#import <UIKit/UIKit.h>
/**
 *  点击按钮的回调
 *
 *  @param selectIndex selectIndex 点击的索引值
 */
typedef void(^DialogViewCompleteHandle)(NSUInteger selectIndex);

@interface ViewController : UIViewController

@property (nonatomic,copy) DialogViewCompleteHandle completeHandle;

- (void)showDialogViewWithHandle:(void (^)(NSUInteger selectIndex))handler;

#define SCREEN_WIDTH [UIScreen mainScreen].bounds.size.width
#define SCREEN_HEIGHT [UIScreen mainScreen].bounds.size.height

#import "ViewController.h"

@interface ViewController ()
{
    UIView *_view;
}
@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
}

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}
- (IBAction)showAlert:(id)sender {

    [self showDialogViewWithHandle:^(NSUInteger selectIndex) {
        if (selectIndex == 0) {
            NSLog(@"第一个按钮被点击了！");
        }else
        {
            NSLog(@"第二个按钮被点击了！");
        }
    }];

}

- (void)showDialogViewWithHandle:(void (^)(NSUInteger selectIndex)) handler
{
    _view = [UIView new];
    _view.center = CGPointMake(SCREEN_WIDTH /2, SCREEN_HEIGHT / 2);
    _view.bounds = CGRectMake(0, 0, SCREEN_WIDTH /2, SCREEN_HEIGHT /2);
    _view.backgroundColor = [UIColor lightGrayColor];
    [self.view addSubview:_view];
    CGRect viewFrame = _view.frame;

    UIButton *button1 = [UIButton buttonWithType:UIButtonTypeRoundedRect];
    button1.center = CGPointMake(viewFrame.size.width /2, viewFrame.size.height /2 - 50);
    button1.bounds = CGRectMake(0, 0, 60, 40);
    button1.tag = 0;
    [button1 setTitle:@"button1" forState:UIControlStateNormal];
    [button1 addTarget:self action:@selector(clickButton:) forControlEvents:UIControlEventTouchUpInside];
    [_view addSubview:button1];

    UIButton *button2 = [UIButton buttonWithType:UIButtonTypeRoundedRect];
    button2.center = CGPointMake(viewFrame.size.width /2, viewFrame.size.height /2 + 50);
    button2.bounds = CGRectMake(0, 0, 60, 40);
    button2.tag = 1;
    [button2 addTarget:self action:@selector(clickButton:) forControlEvents:UIControlEventTouchUpInside];
    [button2 setTitle:@"button2" forState:UIControlStateNormal];
    [_view addSubview:button2];

    _view.transform = CGAffineTransformMakeScale(0.01, 0.01);

    [UIView animateWithDuration:0.3 animations:^{
        _view.transform = CGAffineTransformMakeScale(1.0, 1.0);

    }];

    self.completeHandle = handler;
}

- (void)clickButton:(UIButton *)sender
{
    NSUInteger selIndex = sender.tag;

    if (_completeHandle) {
        _completeHandle(selIndex);
    }

    [self closeView];
}
- (void)closeView{
    [UIView animateWithDuration:0.3 animations:^{
        _view.transform = CGAffineTransformMakeScale(0.01, 0.01);
        [_view removeFromSuperview];
    }];
}
@end

点击button1 和 button2 可以实现按钮的回调Block

Demo下载地址