block全面分析
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//
// RootViewController.m
// UI12_Block传值
//
// Created by dllo on 15/11/24.
// Copyright (c) 2015年 dllo. All rights reserved.
//
#import "RootViewController.h"
#import "SecondViewController.h"
@interface RootViewController ()
@end
@implementation RootViewController
- (void)viewDidLoad {
[super viewDidLoad];
// Do any additional setup after loading the view.
self.view.backgroundColor = [UIColor whiteColor];
self.navigationItem.rightBarButtonItem = [[[UIBarButtonItem alloc] initWithTitle:@"Next" style:UIBarButtonItemStylePlain target:self action:@selector(rightAction:)] autorelease];
void (^block1)(void) = ^(void) {
NSLog(@"aaa");
};
block1();
void (^block2)(NSString *) = ^(NSString *str) {
NSLog(@"%@", str);
};
block2(@"bbb");
}
- (void)rightAction:(UIBarButtonItem *)sender
{
SecondViewController *secondVC = [[SecondViewController alloc] init];
// block会引起self引用计数加一不释放,因此定义一个不关心引用计数的局部变量rootVC
__unsafe_unretained RootViewController *rootVC =self;
void (^colorBlock)(UIColor *) = ^(UIColor *myColor) {
rootVC.view.backgroundColor = myColor;
};
[secondVC sendBlock:colorBlock str:@"庆春是SB"];
[self.navigationController pushViewController:secondVC animated:YES];
[secondVC release];
}
- (void)didReceiveMemoryWarning {
[super didReceiveMemoryWarning];
// Dispose of any resources that can be recreated.
}
/*
#pragma mark - Navigation
// In a storyboard-based application, you will often want to do a little preparation before navigation
- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {
// Get the new view controller using [segue destinationViewController].
// Pass the selected object to the new view controller.
}
*/
@end
//
// SecondViewController.h
// UI12_Block传值
//
// Created by dllo on 15/11/24.
// Copyright (c) 2015年 dllo. All rights reserved.
//
#import <UIKit/UIKit.h>
@interface SecondViewController : UIViewController
{
void (^_myBlock)(UIColor *);
}
- (void)sendBlock:(void (^)(UIColor *))block str:(NSString *)str;
@end
//
// SecondViewController.m
// UI12_Block传值
//
// Created by dllo on 15/11/24.
// Copyright (c) 2015年 dllo. All rights reserved.
//
#import "SecondViewController.h"
@interface SecondViewController ()
@end
@implementation SecondViewController
- (void)dealloc
{
// 引用计数-1
Block_release(_myBlock);
[super dealloc];
}
- (void)viewDidLoad {
[superviewDidLoad];
// Do any additional setup after loading the view.
self.view.backgroundColor = [UIColorredColor];
UIButton *button = [UIButtonbuttonWithType:UIButtonTypeCustom];
button.frame = CGRectMake(50, 50, 50, 50);
button.backgroundColor = [UIColororangeColor];
[button setTitle:@"发春儿"forState:UIControlStateNormal];
[button addTarget:selfaction:@selector(buttonAction:)forControlEvents:UIControlEventTouchUpInside];
[self.viewaddSubview:button];
}
- (void)buttonAction:(UIButton *)sender
{
_myBlock([UIColorgreenColor]);
}
- (void)sendBlock:(void (^)(UIColor *))block str:(NSString *)str
{
NSLog(@"%@", str);
// block([UIColor blueColor]);
// block开空间区域不定,出方法可能会释放, 所以用myblock在堆区复制block的空间
_myBlock = Block_copy(block);
}
- (void)didReceiveMemoryWarning {
[superdidReceiveMemoryWarning];
// Dispose of any resources that can be recreated.
}
/*
#pragma mark - Navigation
// In a storyboard-based application, you will often want to do a little preparation before navigation
- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {
// Get the new view controller using [segue destinationViewController].
// Pass the selected object to the new view controller.
}
*/
@end
//
// RootViewController.m
// UI12_Block传值
//
// Created by dllo on 15/11/24.
// Copyright (c) 2015年 dllo. All rights reserved.
//
#import "RootViewController.h"
#import "SecondViewController.h"
@interface RootViewController ()
@end
@implementation RootViewController
- (void)viewDidLoad {
[superviewDidLoad];
// Do any additional setup after loading the view.
self.view.backgroundColor = [UIColorwhiteColor];
self.navigationItem.rightBarButtonItem = [[[UIBarButtonItemalloc] initWithTitle:@"Next"style:UIBarButtonItemStylePlaintarget:selfaction:@selector(rightAction:)]autorelease];
void (^block1)(void) = ^(void) {
NSLog(@"aaa");
};
block1();
void (^block2)(NSString *) = ^(NSString *str) {
NSLog(@"%@", str);
};
block2(@"bbb");
}
- (void)rightAction:(UIBarButtonItem *)sender
{
SecondViewController *secondVC = [[SecondViewController alloc] init];
#warning block传值1 -定义block, 并通过调用secondVC的方法将block地址传递过去
__unsafe_unretained RootViewController *rootVC =self;
[secondVC sendBlock:^(UIColor *myColor) {
rootVC.view.backgroundColor = myColor;
} str:@"aaa"];
[self.navigationController pushViewController:secondVC animated:YES];
[secondVC release];
}
- (void)didReceiveMemoryWarning {
[super didReceiveMemoryWarning];
// Dispose of any resources that can be recreated.
}
/*
#pragma mark - Navigation
// In a storyboard-based application, you will often want to do a little preparation before navigation
- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {
// Get the new view controller using [segue destinationViewController].
// Pass the selected object to the new view controller.
}
*/
@end
//
// SecondViewController.h
// UI12_Block传值
//
// Created by dllo on 15/11/24.
// Copyright (c) 2015年 dllo. All rights reserved.
//
#import <UIKit/UIKit.h>
typedef void (^blockType)(UIColor *);
@interface SecondViewController : UIViewController
{
#warning block传值3 -定义实例变量, 指向传递来的block, 可供其他方法内调用block
// 也可定义成属性, 要用copy
blockType _myBlock;
}
#warning block传值2 -声明方法, 用来接受block的地址,同事可以顺带接收其他传递值
- (void)sendBlock:(blockType)block str:(NSString *)str;
@end
//
// SecondViewController.m
// UI12_Block传值
//
// Created by dllo on 15/11/24.
// Copyright (c) 2015年 dllo. All rights reserved.
//
#import "SecondViewController.h"
@interface SecondViewController ()
@end
@implementation SecondViewController
- (void)dealloc
{
// 引用计数-1
#warning block传值6 -引用计数减1
Block_release(_myBlock);
[super dealloc];
}
- (void)viewDidLoad {
[superviewDidLoad];
// Do any additional setup after loading the view.
self.view.backgroundColor = [UIColorredColor];
UIButton *button = [UIButtonbuttonWithType:UIButtonTypeCustom];
button.frame = CGRectMake(50, 50, 50, 50);
button.backgroundColor = [UIColororangeColor];
[button setTitle:@"发春儿"forState:UIControlStateNormal];
[button addTarget:selfaction:@selector(buttonAction:)forControlEvents:UIControlEventTouchUpInside];
[self.viewaddSubview:button];
}
- (void)buttonAction:(UIButton *)sender
{
#warning block传值5 =调用block, 传递参数
_myBlock([UIColorgreenColor]);
}
- (void)sendBlock:(blockType)block str:(NSString *)str
{
NSLog(@"%@", str);
// block([UIColor blueColor]);
// block开空间区域不定,出方法可能会释放, 所以用myblock在堆区复制block的空间
#warning block传值4 -将rootVC中定义的block空间拷贝到堆区,防止释放
_myBlock = Block_copy(block);
}
- (void)didReceiveMemoryWarning {
[superdidReceiveMemoryWarning];
// Dispose of any resources that can be recreated.
}
/*
#pragma mark - Navigation
// In a storyboard-based application, you will often want to do a little preparation before navigation
- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {
// Get the new view controller using [segue destinationViewController].
// Pass the selected object to the new view controller.
}
*/
@end
1、第一部分
定义和使用Block,
- (
void
)viewDidLoad
{
[super viewDidLoad];
//(1)定义无参无返回值的Block
void
(^printBlock)() = ^(){
printf
(
"no number"
);
};
printBlock();
printBlock(9);
int
mutiplier = 7;
//(3)定义名为myBlock的代码块,返回值类型为int
int
(^myBlock)(
int
) = ^(
int
num){
return
num*mutiplier;
}
//使用定义的myBlock
int
newMutiplier = myBlock(3);
printf
(
"newMutiplier is %d"
,myBlock(3));
}
//定义在-viewDidLoad方法外部
//(2)定义一个有参数,没有返回值的Block
void
(^printNumBlock)(
int
) = ^(
int
num){
printf
(
"int number is %d"
,num);
};
定义Block变量,就相当于定义了一个函数。但是区别也很明显,因为函数肯定是在-viewDidLoad方法外面定义,而Block变量定义在了viewDidLoad方法内部。当然,我们也可以把Block定义在-viewDidLoad方法外部,例如上面的代码块printNumBlock的定义,就在-viewDidLoad外面。
再来看看上面代码运行的顺序问题,以第(3)个myBlock距离来说,在定义的地方,并不会执行Block{}内部的代码,而在myBlock(3)调用之后才会执行其中的代码,这跟函数的理解其实差不多,就是只要在调用Block(函数)的时候才会执行Block体内(函数体内)的代码。所以上面的简单代码示例,我可以作出如下的结论,
(1)在类中,定义一个Block变量,就像定义一个函数;
(2)Block可以定义在方法内部,也可以定义在方法外部;
(3)只有调用Block时候,才会执行其{}体内的代码;
(PS:关于第(2)条,定义在方法外部的Block,其实就是文件级别的全局变量)
那么在类中定义一个Block,特别是在-viewDidLoad方法体内定义一个Block到底有什么意义呢?我表示这时候只把它当做私有函数就可以了。我之前说过,Block其实就相当于代理,那么这时候我该怎样将其与代理类比以了解呢。这时候我可以这样说:本类中的Block就相当于类自己服从某个协议,然后让自己代理自己去做某个事情。很拗口吧?看看下面的代码,
//定义一个协议
@protocol ViewControllerDelegate<NSObject>
- (
void
)selfDelegateMethod;
@end
//本类实现这个协议ViewControllerDelegate
@interface ViewController ()<ViewControllerDelegate>
@property (nonatomic, assign) id<ViewControllerDelegate> delegate;
@end
接着在-viewDidLoad中的代码如下,
- (
void
)viewDidLoad
{
[super viewDidLoad];
// Do any additional setup after loading the view from its nib.
self.delegate = self;
if
(self.delegate && [self.delegate respondsToSelector:@selector(selfDelegateMethod)]) {
[self.delegate selfDelegateMethod];
}
}
#pragma mark - ViewControllerDelegate method
//实现协议中的方法
- (
void
)selfDelegateMethod
{
NSLog(@
"自己委托自己实现的方法"
);
}
看出这种写法的奇葩地方了吗?自己委托自己去实现某个方法,而不是委托别的类去实现某个方法。本类中定义的一个Block其实就是闲的蛋疼,委托自己去字做某件事情,实际的意义不大,所以你很少看见别人的代码直接在类中定义Block然后使用的,Block很多的用处是跨越两个类来使用的,比如作为property属性或者作为方法的参数,这样就能跨越两个类了。
2、第二部分
__block关键字的使用
在Block的{}体内,是不可以对外面的变量进行更改的,比如下面的语句,
- (
void
)viewDidLoad
{
//将Block定义在方法内部
int
x = 100;
void
(^sumXAndYBlock)(
int
) = ^(
int
y){
x = x+y;
printf
(
"new x value is %d"
,x);
};
sumXAndYBlock(50);
}
这段代码有什么问题呢,Xcode会提示x变量错误信息:Variable is not assigning (missing __block type),这时候给int x = 100;语句前面加上__block关键字即可,如下,
__block
int
x = 100;
这样在Block的{}体内,就可以修改外部变量了。
3、第三部分:Block作为property属性实现页面之间传值
需求:在ViewController中,点击Button,push到下一个页面NextViewController,在NextViewController的输入框TextField中输入一串字符,返回的时候,在ViewController的Label上面显示文字内容,
(1)第一种方法:首先看看通过“协议/代理”是怎么实现两个页面之间传值的吧,
//NextViewController是push进入的第二个页面
//NextViewController.h 文件
//定义一个协议,前一个页面ViewController要服从该协议,并且实现协议中的方法
@protocol NextViewControllerDelegate <NSObject>
- (
void
)passTextValue:(NSString *)tfText;
@end
@interface NextViewController : UIViewController
@property (nonatomic, assign) id<NextViewControllerDelegate> delegate;
@end
//NextViewController.m 文件
//点击Button返回前一个ViewController页面
- (IBAction)popBtnClicked:(id)sender {
if
(self.delegate && [self.delegate respondsToSelector:@selector(passTextValue:)]) {
//self.inputTF是该页面中的TextField输入框
[self.delegate passTextValue:self.inputTF.text];
}
[self.navigationController popViewControllerAnimated:YES];
}
接下来我们在看看ViewController文件中的内容,
//ViewController.m 文件
@interface ViewController ()<NextViewControllerDelegate>
@property (strong, nonatomic) IBOutlet UILabel *nextVCInfoLabel;
@end
//点击Button进入下一个NextViewController页面
- (IBAction)btnClicked:(id)sender
{
NextViewController *nextVC = [[NextViewController alloc] initWithNibName:@
"NextViewController"
bundle:nil];
nextVC.delegate = self;
//设置代理
[self.navigationController pushViewController:nextVC animated:YES];
}
//实现协议NextViewControllerDelegate中的方法
#pragma mark - NextViewControllerDelegate method
- (
void
)passTextValue:(NSString *)tfText
{
//self.nextVCInfoLabel是显示NextViewController传递过来的字符串Label对象
self.nextVCInfoLabel.text = tfText;
}
这是通过“协议/代理”来实现的两个页面之间传值的方式。
(2)第二种方法:使用Block作为property,实现两个页面之间传值,
先看看NextViewController文件中的内容,
//NextViewController.h 文件
@interface NextViewController : UIViewController
@property (nonatomic, copy)
void
(^NextViewControllerBlock)(NSString *tfText);
@end
//NextViewContorller.m 文件
- (IBAction)popBtnClicked:(id)sender {
if
(self.NextViewControllerBlock) {
self.NextViewControllerBlock(self.inputTF.text);
}
[self.navigationController popViewControllerAnimated:YES];
}
再来看看ViewController文件中的内容,
- (IBAction)btnClicked:(id)sender
{
NextViewController *nextVC = [[NextViewController alloc] initWithNibName:@
"NextViewController"
bundle:nil];
nextVC.NextViewControllerBlock = ^(NSString *tfText){
[self resetLabel:tfText];
};
[self.navigationController pushViewController:nextVC animated:YES];
}
#pragma mark - NextViewControllerBlock method
- (
void
)resetLabel:(NSString *)textStr
{
self.nextVCInfoLabel.text = textStr;
}
好了就这么多代码,可以使用Block来实现两个页面之间传值的目的,实际上就是取代了Delegate的功能。
另外,博客中的代码Sample Code可以再Github下载,如果因为Github被墙了,可以在终端使用git clone + 完整链接,即可克隆项目到本地。
Github中的代码,可以开启两种调试模式,你需要在项目的配置文件BlockSamp-Prefix.pch中注释或者解注释下面的代码,
#define Debug_BlcokPassValueEnable
即可开启两种调试的方式,如果注释了上面的语句就是使用Delegate进行调试;否则使用Block进行调试。
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