iOS開展block說明

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淺談block使用方法

對於block他用著確實方便,好多人都非常迷茫,這裡寫了一個Demo解說block的使用方法

好多人都覺得block是用於後一個介面向前一個介面傳值用的,事實上更詳細的說是經常使用來介面之間的傳值,事實上僅僅要須要傳值不管是view之間還是controller之間還是view與controller之間都能夠用block,當傳值比較少時用block比使用代理更方便.

block建立後都在棧區存放的,block的語義特性必須用copy,通過copy能夠將block從棧區放到堆區,保證每次使用block時block都存在,因此我們使用時經常要定義屬性,使用屬性是為了儲存該block變數

例如以下舉個範例解說

首先在project中建立兩個類BlockViewController和BlockView

在BlockView中僅僅是為了建立幾個button,在BlockViewController中使用,能夠降低BlockViewController的代碼任務量,可是BlockView中僅僅有一個執行個體變數button是,而且在延展中定義的,外部無法訪問到,當我們為button加入點擊觸發事件就須要獲得button的tag值,這時就要把所點擊button的tag擷取到,來為不同的button加入響應事件

在BlockView.h中定義一個block變數和一個方法,方法的參數是block類型的

#import <UIKit/UIKit.h>//第一步：聲明blocktypedef void(^ButtonActionBlock)(NSInteger tag);@interface BlockView : UIView-(void)buttonActionBlock:(ButtonActionBlock)didClickButton;@end

在BlockView.m中

<pre name="code" class="objc">#import "BlockView.h"@interface BlockView ()//Block//block建立後都在棧區存放的,block的語義特性必須用copy,通過copy能夠將block從棧區放到堆區,保證每次使用block時block都存在@property (nonatomic, copy) ButtonActionBlock buttonActionBlock;@property (nonatomic, strong) UIButton *button;@end@implementation BlockView- (id)initWithFrame:(CGRect)frame{    self = [super initWithFrame:frame];    if (self) {        CGFloat x = 5;        CGFloat y = 5;        CGFloat width = 65;        CGFloat height = 40;        //建立button        for (int i = 0; i < 4; i ++) {            self.button = [UIButton buttonWithType:(UIButtonTypeSystem)];            self.button.frame = CGRectMake(x + i * (width + 10), y, width, height);            self.button.tag = 100 + i;            self.button.backgroundColor = [UIColor cyanColor];            self.button.layer.cornerRadius = 5;            self.button.layer.masksToBounds = YES;            [self.button setTitle:[NSString stringWithFormat:@"%d",i] forState:UIControlStateNormal];            [self.button addTarget:self action:@selector(handleButton:) forControlEvents:UIControlEventTouchUpInside];            [self addSubview:_button];        }    }    return self;}//處理button的點擊事件,將tag值傳給block的參數回調block-(void)handleButton:(UIButton *)button{    NSLog(@"???????????????3");    NSInteger tag = button.tag;   //第二步，回掉block   self.buttonActionBlock(tag),NSLog(@"???????????????6");    NSLog(@"???????????????7");    }//該方法中self.buttonActionBlock = didClickButton;運行後會調用屬性buttonActionBlock的setter方法,將block變數didClickButton傳給setter方法的參數-(void)buttonActionBlock:(ButtonActionBlock)didClickButton{    NSLog(@"???????????????1");    NSLog(@"-----------didClickButton = %p",didClickButton);    self.buttonActionBlock = didClickButton;    }//重寫屬性buttonActionBlock的setter方法,在此重寫setter方法目的是為了表明該方法是把傳進來的block變數進行深拷貝,複製到了堆區,並賦給了執行個體變數buttonActionBlock,使我們在不論什麼時候都能使用block變數(block的建立後在棧區,出了方法就被回收,無法再使用)- (void)setButtonActionBlock:(ButtonActionBlock)buttonActionBlock{    NSLog(@"???????????????2");    if (_buttonActionBlock != buttonActionBlock) {        NSLog(@"++++++++buttonActionBlock = %p",buttonActionBlock);        _buttonActionBlock = [buttonActionBlock copy];    }}@end

BlockViewController.m檔案裡匯入BlockView.h檔案

BlockViewController.m檔案中代碼實現

#import "BlockViewController.h"#import "BlockView.h"// 擷取RGB顏色#define RGBA(r,g,b,a) [UIColor colorWithRed:r/255.0f green:g/255.0f blue:b/255.0f alpha:a]@interface BlockViewController ()<UIScrollViewDelegate>@property (nonatomic, strong) UIImageView *YJFImageView;@end@implementation BlockViewController- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil{    self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];    if (self) {            }    return self;}- (void)viewDidLoad{    [super viewDidLoad];    self.view.backgroundColor = RGBA(252, 230, 201, 1.0);    BlockView *blockView = [[BlockView alloc] initWithFrame:CGRectMake(10, 0, 320 - 20, 50)];    blockView.backgroundColor = [UIColor lightGrayColor];    [self.view addSubview:blockView];    //BlockView的對象blockView調用其方法buttonActionBlock:   //第三步。調用block   [blockView buttonActionBlock:^(NSInteger tag) {        //block的實現        NSLog(@"???????????????4");        [self handleButton:tag];        NSLog(@"???????????????5");            }];    [self createView];}//處理自己定義toolBar的點擊事件-(void)handleButton:(NSInteger)tag{        switch (tag) {            //...button        case 100:        {            self.YJFImageView.image = LOADIMAGE(@"2", @"jpg");        }            break;                        //...button        case 101:        {            self.YJFImageView.image = LOADIMAGE(@"5", @"jpg");        }            break;                        //...button        case 102:        {            self.YJFImageView.image = LOADIMAGE(@"6", @"jpg");        }            break;                        //...button        case 103:        {            self.YJFImageView.image = LOADIMAGE(@"4", @"jpg");        }            break;                    default:            break;    }}-(void)createView{    self.YJFImageView = [[UIImageView alloc] initWithFrame:CGRectMake(10, 52, 320 - 20, 568 - 64 - 75)];    self.YJFImageView.image = LOADIMAGE(@"8", @"jpg");    self.YJFImageView.userInteractionEnabled = YES;            [self.view addSubview:_YJFImageView];}- (void)didReceiveMemoryWarning{    [super didReceiveMemoryWarning];    // Dispose of any resources that can be recreated.}@end

通過程式執行控制台輸出結果例如以下:

點擊button前:

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由此結合代碼實現中打的log能夠看出

<pre name="code" class="objc">didClickButton和傳入屬性的setter方法的參數是一個地址,則

,BlockView.m檔案裡

<pre name="code" class="objc">buttonActionBlock:方法中把didClickButton拷貝了一份到棧區,賦值給執行個體變數_buttonActionBlock

點擊button後:

結合代碼實現中打的log能夠看出整個Block的運行過程,也能夠通過打斷的查看Block的運行過程

著作權聲明：本文博主原創文章。部落格，未經同意不得轉載。

iOS開展block說明