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(0, 0, SCREEN_WIDTH, 50) title:@"请选择收藏位置" titleColor:HMColor(13, 195, 176) alignmentType:NSTextAlignmentCenter size:16]; 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(0, 0, 30, 30) 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 50; } #pragma mark - UITableViewDelegate #pragma mark - Optional - (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath{ UITableViewCell *cell = [tableView cellForRowAtIndexPath:indexPath]; cell.accessoryView = [UIButton createButton:CGRectMake(0, 0, 30, 30) 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(0, 0, 30, 30) 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(0, 0, 260, 200) 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(51, 51, 51, 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(0, 0, SCREEN_WIDTH, 50) title:@"请选择收藏位置" titleColor:HMColor(13, 195, 176) alignmentType:NSTextAlignmentCenter size:16]; 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(0, 0, 30, 30) 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 50; } #pragma mark - UITableViewDelegate #pragma mark - Optional - (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath{ UITableViewCell *cell = [tableView cellForRowAtIndexPath:indexPath]; cell.accessoryView = [UIButton createButton:CGRectMake(0, 0, 30, 30) 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(0, 0, 30, 30) 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(0, 0, 260, 200) 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(51, 51, 51, 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！ 程序猿神奇的手，每时每刻，这双手都在改变着世界的交互方式！ 本文转自当天真遇到现实博客园博客，原文链接：http://www.cnblogs.com/XYQ-208910/p/5512618.html ，如需转载请自行联系原作者
