记录 ios 开发过程中遇到的问题及心得
#1.常见书写方式
dispatch_group_t group = dispatch_group_create();
dispatch_queue_t queue = dispatch_queue_create("com.formssi.get_product_detail", NULL);
dispatch_group_async(group,queue, ^{
<!--do work-->
});
dispatch_group_async(group,queue, ^{
<!--do work-->
});
dispatch_group_notify(group, dispatch_get_main_queue(), ^{
<!--main thread-->
<!--do work-->
});
#2.如果做的事包含block任务，就需要给没个block任务添加入组与出组的操作
dispatch_group_t group = dispatch_group_create();
dispatch_queue_t queue = dispatch_queue_create("com.baidu.detail", NULL);
dispatch_group_enter(group);
dispatch_group_async(group,queue, ^{
<!--do block work-->
dispatch_group_leave(group);
});
dispatch_group_enter(group);
dispatch_group_async(group,queue, ^{
<!--do block work-->
dispatch_group_leave(group);
});
dispatch_group_notify(group, dispatch_get_main_queue(), ^{
<!--main thread-->
<!--do work-->
});
#3.当我们使用其他的三方库做网络请求或则图片下载时，而请求的任务包含多个，需要 等待这些任务都执行完成之后，再返回结果，如下列子：
dispatch_group_t group = dispatch_group_create();
__block BOOL isSuccess = NO;
for (CellModel *cellModel in modelArray) {
<!--异步下载图片-->
dispatch_group_enter(group);
[[SDWebImageManager sharedManager] downloadImageWithURL:cellModel.url options:SDWebImageRetryFailed | SDWebImageLowPriority progress:nil completed:^(UIImage *image, NSError *error, SDImageCacheType cacheType, BOOL finished, NSURL *imageURL) {
NSLog(@"downloadError = %@-%@",error,[NSThread currentThread]);
if (error) {
isSuccess = NO;
}else{
isSuccess = YES;
<!-- 获取图片大小-->
cellModel.cellHeight = WidthOfWindow * image.size.height / image.size.width;
}
dispatch_group_leave(group);
}];
}
dispatch_group_notify(group, dispatch_get_main_queue(), ^{
<!-- more -->
if (isSuccess) {
completion(NetWorkingResultTypeSuccess,@"success");
}else{
completion(NetWorkingResultTypeNoData, @"error");
}
});
自定定义返回按钮时，系统自带的滑动返回手势会失效:
新建一个类，继承UINavigationController，重写pushViewController: animated: 方法，如下：
-(void)pushViewController:(UIViewController *)viewController animated:(BOOL)animated{
if (self.viewControllers.count > 0) {
// 影藏TabBar
viewController.hidesBottomBarWhenPushed = YES;
// 自定义返回按钮
viewController.navigationItem.leftBarButtonItem = [[UIBarButtonItem alloc]initWithImage:[UIImage imageNamed:@"navigationbar_back"] style:UIBarButtonItemStylePlain target:self action:@selector(popBack)];
}
[super pushViewController:viewController animated:animated];
}
解决方式一：
- (void)viewDidLoad {
[super viewDidLoad];
// 返回手势的代理
self.interactivePopGestureRecognizer.delegate = self;
}
// 实现代理方法
- (BOOL)gestureRecognizer:(UIGestureRecognizer *)gestureRecognizer shouldReceiveTouch:(UITouch *)touch{
// 非根控制器才接受手势
BOOL result = self.childViewControllers.count > 1;
return result;
}
方式二：
@interface RootNavigationController ()<UINavigationControllerDelegate>
{
id _popDelegate;
}
@end
@implementation RootNavigationController
- (void)viewDidLoad {
[super viewDidLoad];
// 记录滑动代理的的值
_popDelegate = self.interactivePopGestureRecognizer.delegate;
self.delegate = self;
}
@end
//代理方法 导航控制器跳转完成的时候调用
-(void)navigationController:(UINavigationController *)navigationController didShowViewController:(UIViewController *)viewController animated:(BOOL)animated{
if (viewController == self.viewControllers.firstObject) {//显示根控制器
//还原滑动手势的代理
self.interactivePopGestureRecognizer.delegate = _popDelegate;
}else{//不是根控制器
//实现滑动返回功能
//清空滑动返回手势的代理，就能实现滑动功能
self.interactivePopGestureRecognizer.delegate = nil;
}
}