iOS:使用block代码块实现事件处理过程中的回调

block是什么，这里就不多加强调了，它的优点：

第一：执行效率高，速度快

第二：使用起来比代理简单，省却不少代码，增强代码美感

有一些小的知识点要强调一下：

第一点：它类似于一个匿名函数，也跟java中的匿名内部类相似，但是，记住，它是一种数据类型，因为它内部是一个结构体，有方法有属性，所以它具有对象的特征；

第二点：在类中声明block为属性时，如果使用assgin修饰，那么它被放到了栈中，方法已过就会被销毁，所以，尽量使用copy作为修饰词，这样一来block就被存放到了堆中，生命周期就会延长，保证block不会被立即销毁；

第三点：要防止循环引用，造成线程死锁，所以，有时需要加上__weak修饰。

第四点：为什么多用copy修饰，而不用strong修饰，这是MRC时期遗留下来的写法习惯，其实用strong也可以修饰，但是尽量用copy。

block既可以作为属性，单独赋值然后回调；也可以作为一个方法的参数使用，再进行回调，举例如下，直接代码演示：

我的例子过程大概是：首先用户浏览题库时，点击收藏按钮，弹出收藏界面，用户选择完某一个文件夹后，隐藏收藏界面，提示收藏成功！

例子一：block使用属性单独赋值后回调

这是收藏界面类的回调代码

#import <UIKit/UIKit.h>

//声明block,用作选择收藏文件后的回调处理
typedef void (^CollectionBlock)();     //选择文件夹
typedef void (^CompleteHandleBlock)(); //选完之后的处理

@interface KJCollectionView : UITableView
@property (copy,nonatomic)CollectionBlock collectionBlock;
@property (copy,nonatomic)CompleteHandleBlock completeBlock;
-(instancetype)initWithFrame:(CGRect)frame withFiles:(NSArray *)files;

@end

#import "KJCollectionView.h"
#import "KJMyQueBankFile.h"

@interface KJCollectionView()<UITableViewDataSource,UITableViewDelegate>
@property (strong,nonatomic)NSArray *allFiles;
@end

@implementation KJCollectionView

-(instancetype)initWithFrame:(CGRect)frame withFiles:(NSArray *)files
{
    self = [super initWithFrame:frame];
    if (self) {
        self.dataSource = self;
        self.delegate = self;
        self.tableHeaderView = [UILabel createLabel:CGRectMake(, , SCREEN_WIDTH, ) title:@"请选择收藏位置" titleColor:HMColor(, , ) alignmentType:NSTextAlignmentCenter size:];
        self.tableFooterView = [[UIView alloc]initWithFrame:CGRectZero];
        self.allFiles = [NSArray arrayWithArray:files];
        MoveUnderLine(self);
    }
    return self;
}

#pragma mark - block回调,为block属性赋值
-(void)setCollectionBlock:(CollectionBlock)collectionBlock{
    if (_collectionBlock != collectionBlock) {
       _collectionBlock = collectionBlock;
    }
}
-(void)setCompleteBlock:(CompleteHandleBlock)completeBlock{
    if (_completeBlock != completeBlock) {
        _completeBlock = completeBlock;
    }
}

#pragma mark - UITableViewDataSource
#pragma mark - Required

-(NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section{
    return self.allFiles.count;
}

-(UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath{

    static NSString *reuseIdentifier = @"Cell";
    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:reuseIdentifier];
    if (!cell) {
        cell = [[UITableViewCell alloc]init];
    }
    cell.accessoryView = [UIButton createButton:CGRectMake(, , , ) imageName:@"default_true" target:self Done:@selector(chooseFileDone:)];
    cell.imageView.image = [UIImage imageNamed:[self.allFiles[indexPath.row] file_image]];
    cell.textLabel.text = [self.allFiles[indexPath.row] file_Name];
    return cell;
}

#pragma mark - Optional
- (CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath{
    return ;
}

#pragma mark - UITableViewDelegate
#pragma mark - Optional
- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath{
    UITableViewCell *cell = [tableView cellForRowAtIndexPath:indexPath];
    cell.accessoryView = [UIButton createButton:CGRectMake(, , , ) imageName:@"selected_ture" target:nil Done:nil];

    //回调处理
    _collectionBlock();
    _completeBlock();
}

#pragma mark - 按钮选择文件夹
-(void)chooseFileDone:(UIButton *)btn{
    UITableViewCell *cell = (UITableViewCell *)btn.superview;
    cell.accessoryView = [UIButton createButton:CGRectMake(, , , ) imageName:@"selected_ture" target:nil Done:nil];

    //回调处理
    _collectionBlock();
    _completeBlock();
}
@end

这是在题库类中给block传递回调处理的代码：直接通过属性赋值

#pragma mark - 点击收藏按钮时的代理方法
/**
 *  收藏作业
 *  @param indexPath     当前cell中选择按钮选中后的cell
 *  @param btn           收藏按钮
 *  @param collectionTag 当前cell中收藏按钮的tag
 */
-(void)finishedClickedCollectionFileIndexPath:(NSIndexPath *)indexPath CollectionBtn:(UIButton *)btn{

    //创建收藏文件夹视图和蒙版视图
    self.collectionView = [[KJCollectionView alloc]initWithFrame:CGRectMake(, , , ) withFiles:self.filesArrayM];
    self.collectionView.layer.cornerRadius = 3.0;
    self.collectionView.layer.masksToBounds = YES;
    self.collectionView.center = [UIApplication sharedApplication].keyWindow.center;
    self.coverView = [[UIView alloc]initWithFrame:self.view.bounds];
    self.coverView.backgroundColor = HMColorRGBA(, , , 0.3);
    [self.view addSubview:self.collectionView];
    [self.view addSubview:self.coverView];
    [self.view insertSubview:self.collectionView aboveSubview:self.coverView];
    __weak typeof(self) weakSelf = self;

   //为选择文件的block赋值
    self.collectionView.collectionBlock = ^(){
        //取出收藏字典
        KJChooseHomeworkDicM *checkBtnDicManager = [KJChooseHomeworkDicM sharedCheckBtnDicMManager];
        [checkBtnDicManager.collectionDicM setObject:indexPath forKey:indexPath];
        [btn setSelected:YES];
        //获取作业模型
        KJLog(@"clickedCollection:%@",[weakSelf.homeworkCellFrames[indexPath.row] defaultFH]);

    };

   //为选完文件后的block赋值
    self.collectionView.completeBlock = ^(){
        [MBProgressHUD showSuccess:@"收藏成功"];
        //移除收藏文件夹视图和蒙版视图
        dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(0.5 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
            [weakSelf.collectionView removeFromSuperview];
            [weakSelf.coverView removeFromSuperview];
            [weakSelf setCollectionView:nil];
            [weakSelf setCoverView:nil];
        });
    };
}

例子二：block作为方法的参数赋值后再进行回调

这是收藏界面类的回调代码

#import <UIKit/UIKit.h>

//声明block,用作选择收藏文件后的回调处理
typedef void (^CollectionBlock)();     //选择文件夹
typedef void (^CompleteHandleBlock)(); //选完之后的处理

@interface KJCollectionView : UITableView
@property (copy,nonatomic)CollectionBlock collectionBlock;
@property (copy,nonatomic)CompleteHandleBlock completeBlock;
-(instancetype)initWithFrame:(CGRect)frame withFiles:(NSArray *)files;

//声明一个方法
-(void)chooseFile:(CollectionBlock )collectionBlock compeleteChooseBlock:(CompleteHandleBlock)completeBlock;
@end

//  Created by mac on 16/5/20.
//  Copyright © 2016年 mac. All rights reserved.
#import "KJCollectionView.h"
#import "KJMyQueBankFile.h"

@interface KJCollectionView()<UITableViewDataSource,UITableViewDelegate>
@property (strong,nonatomic)NSArray *allFiles;
@end

@implementation KJCollectionView

-(instancetype)initWithFrame:(CGRect)frame withFiles:(NSArray *)files
{
    self = [super initWithFrame:frame];
    if (self) {
        self.dataSource = self;
        self.delegate = self;
        self.tableHeaderView = [UILabel createLabel:CGRectMake(, , SCREEN_WIDTH, ) title:@"请选择收藏位置" titleColor:HMColor(, , ) alignmentType:NSTextAlignmentCenter size:];
        self.tableFooterView = [[UIView alloc]initWithFrame:CGRectZero];
        self.allFiles = [NSArray arrayWithArray:files];
        MoveUnderLine(self);
    }
    return self;
}

#pragma mark - block回调,通过方法为block属性赋值
-(void)chooseFile:(CollectionBlock )collectionBlock compeleteChooseBlock:(CompleteHandleBlock)completeBlock{

    if (_collectionBlock != collectionBlock) {
        _collectionBlock = collectionBlock;
    }
    if (_completeBlock != completeBlock) {
        _completeBlock = completeBlock;
    }
}

#pragma mark - UITableViewDataSource
#pragma mark - Required

-(NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section{
    return self.allFiles.count;
}

-(UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath{

    static NSString *reuseIdentifier = @"Cell";
    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:reuseIdentifier];
    if (!cell) {
        cell = [[UITableViewCell alloc]init];
    }
    cell.accessoryView = [UIButton createButton:CGRectMake(, , , ) imageName:@"default_true" target:self Done:@selector(chooseFileDone:)];
    cell.imageView.image = [UIImage imageNamed:[self.allFiles[indexPath.row] file_image]];
    cell.textLabel.text = [self.allFiles[indexPath.row] file_Name];
    return cell;
}

#pragma mark - Optional
- (CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath{
    return ;
}

#pragma mark - UITableViewDelegate
#pragma mark - Optional
- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath{
    UITableViewCell *cell = [tableView cellForRowAtIndexPath:indexPath];
    cell.accessoryView = [UIButton createButton:CGRectMake(, , , ) imageName:@"selected_ture" target:nil Done:nil];

    //回调处理
    _collectionBlock();
    _completeBlock();
}

#pragma mark - 按钮选择文件夹
-(void)chooseFileDone:(UIButton *)btn{
    UITableViewCell *cell = (UITableViewCell *)btn.superview;
    cell.accessoryView = [UIButton createButton:CGRectMake(, , , ) imageName:@"selected_ture" target:nil Done:nil];

    //回调处理
    _collectionBlock();
    _completeBlock();
}
@end

这是在题库类中给block传递回调处理的代码：直接将要赋值的block写入到方法中

#pragma mark - 点击收藏按钮时的代理方法
/**
 *  收藏作业
 *  @param indexPath     当前cell中选择按钮选中后的cell
 *  @param btn           收藏按钮
 *  @param collectionTag 当前cell中收藏按钮的tag
 */
-(void)finishedClickedCollectionFileIndexPath:(NSIndexPath *)indexPath CollectionBtn:(UIButton *)btn{

    //创建收藏文件夹视图和蒙版视图
    self.collectionView = [[KJCollectionView alloc]initWithFrame:CGRectMake(, , , ) withFiles:self.filesArrayM];
    self.collectionView.layer.cornerRadius = 3.0;
    self.collectionView.layer.masksToBounds = YES;
    self.collectionView.center = [UIApplication sharedApplication].keyWindow.center;
    self.coverView = [[UIView alloc]initWithFrame:self.view.bounds];
    self.coverView.backgroundColor = HMColorRGBA(, , , 0.3);
    [self.view addSubview:self.collectionView];
    [self.view addSubview:self.coverView];
    [self.view insertSubview:self.collectionView aboveSubview:self.coverView];
    __weak typeof(self) weakSelf = self;

    //把block放入方法中
    [self.collectionView chooseFile:^{
        //取出收藏字典
        KJChooseHomeworkDicM *checkBtnDicManager = [KJChooseHomeworkDicM sharedCheckBtnDicMManager];
        [checkBtnDicManager.collectionDicM setObject:indexPath forKey:indexPath];
        [btn setSelected:YES];
        [MBProgressHUD showSuccess:@"收藏成功"];

        //获取作业模型
        KJLog(@"clickedCollection:%@",[weakSelf.homeworkCellFrames[indexPath.row] defaultFH]);

    } compeleteChooseBlock:^{

        //移除收藏文件夹视图和蒙版视图
        dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(0.5 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
            [MBProgressHUD hideHUD];
            [weakSelf.collectionView removeFromSuperview];
            [weakSelf.coverView removeFromSuperview];
            [weakSelf setCollectionView:nil];
            [weakSelf setCoverView:nil];
        });
    }];
}

上面两种演示截图达到的效果是一样的：

点击题库中的收藏　　　　　　　　　　　　　　　　　　　　　选择文件夹收藏     　

　　　　

显示收藏成功　　　　　　　　　　　　　　　　　　　　　　移除文件夹视图

　　  

本人原创，转载须注明出处，谢谢！