UI_Block

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这里写图片描述

RootViewController.m#import "RootViewController.h"#import "SecondViewController.h"@interface RootViewController ()@end@implementation RootViewController- (void)viewDidLoad {    [super viewDidLoad];    // Do any additional setup after loading the view.    UIButton *button = [UIButton buttonWithType:UIButtonTypeSystem];    button.frame = CGRectMake(100, 100, 150, 50);    [self.view addSubview:button];    button.layer.borderWidth = 1;    [button setTitle:@"下一页" forState:UIControlStateNormal];    [button addTarget:self action:@selector(click:) forControlEvents:UIControlEventTouchUpInside];    // 函数指针是保存函数地址的指针,函数指针的类型先把函数名字拿掉,然后写一个小括号,这个括号不能省略,然后里面写*和变量名,最后把形参名拿掉.    int (*p)(int, int) = maxValue;    NSLog(@"%d", p(10, 20));    }- (void)click:(UIButton *)button {1.等号左边:先写返回值类型,然后(),里面写^和block的名字,然后在()里写参数类型,把函数指针的*p变成^block.2.等号右边:先以^开头,然后写形参列表,列表里的形参要和等号左边的形参类型和顺序相应,最后写函数部分.3.注意有返回值的block一定要写return,在最后以分号结尾.    int (^block)(int, int) = ^(int a, int b) {        // 函数体        return 10;    };    NSLog(@"%d", block(10, 20));    // 无参,无返回值.    void (^block)() = ^{        NSLog(@"1");    };    // 不调用,block就不会被执行.    block();    // block的类型.    // 等号左边去掉block的名剩下的就是block的类型    void (^block)(float, float, float, float) = ^(float R, float G, float B, float A){        self.view.backgroundColor = [UIColor colorWithRed:R green:G blue:B alpha:A];    };    block(arc4random() % 256 / 255.0, arc4random() % 256 / 255.0, arc4random() % 256 / 255.0, 1);    SecondViewController *second = [[SecondViewController alloc] init];    [self.navigationController pushViewController:second animated:YES];    [second release];1.写一个block,没有参数没有返回值,改变背景颜色.void (^block)() = ^{        self.view.backgroundColor = [UIColor colorWithRed:arc4random() % 256 / 255.0 green:arc4random() % 256 / 255.0 blue:arc4random() % 256 / 255.0 alpha:1];    };    2.传值,这次我们传一个block    second.block = block;    3.没有返回值,参数是一个字符串    void (^block)(NSString *) = ^(NSString *str) {        NSLog(@"%@", str);        // 对数据的处理,操作,都在block里面写    };    second.block = block;void (^block1)() = ^(){    };    NSLog(@"%p", block1);    int a = 10;    void (^block2)() = ^(){        NSLog(@"%d", a);    };    NSLog(@"%p", block2);    // block 如果不进行拷贝的话,可能会在栈区或者全局区,这两个区不能对它进行内存上的控制,所以不安全,所以用一个copy,就可以把block拷贝一份到堆区.    }

SecondViewController.h#import <UIKit/UIKit.h>typedef void(^Block)(NSString *);   // block的另一种写法@interface SecondViewController : UIViewController@property(nonatomic, copy)Block block;1.写一条属性,用来接收前一页的block.@property(nonatomic, copy)void(^block)();@end

SecondViewController.m#import "SecondViewController.h"@interface SecondViewController ()@end@implementation SecondViewController- (void)dealloc{    // block作为属性释放用它自己提供的方法    Block_release(_block);    [super dealloc];}- (void)viewDidLoad {    [super viewDidLoad];    // Do any additional setup after loading the view.    self.view.backgroundColor = [UIColor whiteColor];    UIButton *button = [UIButton buttonWithType:UIButtonTypeSystem];    button.frame = CGRectMake(100, 100, 150, 50);    [self.view addSubview:button];    button.layer.borderWidth = 1;    [button setTitle:@"返回" forState:UIControlStateNormal];    [button addTarget:self action:@selector(click:) forControlEvents:UIControlEventTouchUpInside];}- (void)click:(UIButton *)button {    [self.navigationController popToRootViewControllerAnimated:YES];    // 调用block,将block中赋一个字符串传回去    self.block();    self.block(@"哈哈");}

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