定时改变App主题的方案

1.将接口返回的图片缓存到本地，由于写data到本地是耗时操作，为了不阻塞主线程，可开启子线程来做此操作

 dispatch_queue_t queue = dispatch_queue_create("cn.xxx.queue", DISPATCH_QUEUE_SERIAL);
    // 异步存到沙盒
    dispatch_async(queue, ^{

        for (XWMainBtnSkinModel *skinM in self.models) {

            //  btn_Bottom_4
            NSString *path =  [skinM.btnKey cacheDirWithSubpath:@"tabbar"];

            // 下载图片
            NSData *data = [NSData dataWithContentsOfURL:[NSURL URLWithString:skinM.img]];

            [data writeToFile:path atomically:YES];

           if([skinM.type isEqualToString:@""]){

                // btn_Bottom_4_sel
                NSString *selImgKey = [NSString stringWithFormat:@"%@_sel",skinM.btnKey];
                NSString *selpath =  [selImgKey cacheDirWithSubpath:@"tabbar"];

                // 下载图片
                NSData *selImgData = [NSData dataWithContentsOfURL:[NSURL URLWithString:skinM.selImg]];

                [selImgData writeToFile:selpath atomically:YES];
            }
        }

    });

2.将请求到的图片，保存到内存，并给UI控件赋值，此处以tabbar为例

    UIImage *img = [[UIImage alloc] init];
    UIImage *selImg = [[UIImage alloc] init];
    int i = ;
     for (UITabBarItem *item in self.tabBar.items) {
         if(isNet){// 如果是从网络上获取，要告诉系统是@2x的图片
             img =  [UIImage imageWithData:[NSData dataWithContentsOfURL:[NSURL URLWithString:imgs[i]]] scale:2.0];
             selImg = [UIImage imageWithData:[NSData dataWithContentsOfURL:[NSURL URLWithString:selImgs[i]]] scale:2.0];
         }else{
             img =  [UIImage imageNamed:imgs[i]];
             selImg = [UIImage imageNamed:selImgs[i]];
         }

        item.image = [img imageWithRenderingMode:UIImageRenderingModeAlwaysOriginal];

        item.selectedImage = [selImg imageWithRenderingMode:UIImageRenderingModeAlwaysOriginal];
        i++;
    }

3.第二次打开app时，判断本地是否有缓存文件，如果有，就取之前缓存中的文件（这样用户体验更好，省去去网络上下载图片）

    if (!isExist) { // 如果cache/tabbar这个目录不存在，就用默认主题
        [self setUpChildController:mainPage title:@"首页" image:@"img_btn_mainpage_normal.png" selectedImage:@"img_btn_mainpage_select.png"];

        [self setUpChildController:departClass title:@"分类" image:@"img_btn_class_normal" selectedImage:@"img_btn_class_select"];

        [self setUpChildController:theme title:@"" image:@"img_btn_theme" selectedImage:@"img_btn_theme"];

        [self setUpChildController:message title:@"消息" image:@"img_btn_message_normal" selectedImage:@"img_btn_message_select"];

        [self setUpChildController:me title:@"我" image:@"img_btn_me_normal" selectedImage:@"img_btn_me_select"];

        self.selectedIndex = ;

        // 矫正TabBar图片位置，使之垂直居中显示
        CGFloat offset = 3.0;
        for (UITabBarItem *item in self.tabBar.items) {
            item.imageInsets = UIEdgeInsetsMake(offset, , -offset, );
            if([item.title isEqualToString:@""])
            {
                item.imageInsets = UIEdgeInsetsMake(, , -, );
            }
        }
    } else {    //存在

        [self setUpNetDataChildController:mainPage title:@"首页" image:@"btn_Bottom_1" selectedImage:@"btn_Bottom_1_sel"];
        [self setUpNetDataChildController:departClass title:@"分类" image:@"btn_Bottom_2" selectedImage:@"btn_Bottom_2_sel"];
        [self setUpNetDataChildController:theme title:@"" image:@"btn_Bottom_3" selectedImage:@"btn_Bottom_3_sel"];
        [self setUpNetDataChildController:message title:@"消息" image:@"btn_Bottom_4" selectedImage:@"btn_Bottom_4_sel"];
        [self setUpNetDataChildController:me title:@"我" image:@"btn_Bottom_5" selectedImage:@"btn_Bottom_5_sel"];

        self.selectedIndex = ;

        // 矫正TabBar图片位置，使之垂直居中显示
        CGFloat offset = 3.0;
        for (UITabBarItem *item in self.tabBar.items) {
            item.imageInsets = UIEdgeInsetsMake(offset, , -offset, );
            if([item.title isEqualToString:@""])
            {
                item.imageInsets = UIEdgeInsetsMake(, , -, );
            }
        }

    }

4.如果到了主题的过期时间，就应该切换回默认的主题：从接口中获取到主题到期时间，并设置定时器，当到期后，就删除本地缓存，并不在处理接口返回的图片数据。（直到接口中的到期时间重设，才处理接口中的图片）

    [[NetRequest request]dataRequest:nil apiURL:__getSkinBtnImg needToCache:nil completeBlock:^(id result) {

        self.models = [XWMainBtnSkinModel mj_objectArrayWithKeyValuesArray:result[@"btnImg"]];
        if(self.models.count >  ){

            XWMainBtnSkinModel *model = self.models[];
            NSDateFormatter *date=[[NSDateFormatter alloc] init];
            //        endTime: "2016-04-16 16:45:59"
            [date setDateFormat:@"yyyy-MM-dd HH:mm:ss"];

           /**服务返回的主题到期时间*/
            NSDate *d=[date dateFromString:model.endTime];
            NSTimeInterval late = [d timeIntervalSince1970];

            NSDate *now = [NSDate date];
            NSTimeInterval nowtiem = [now timeIntervalSince1970];
            NSTimeInterval cha = late - nowtiem;
            /**到期时间和当前时间的差值*/
            self.cha = cha;
            // 定时器（到期了就切回之前的默认主题）
            NSTimer *timer = [NSTimer scheduledTimerWithTimeInterval:cha target:self selector:@selector(returnSkan) userInfo:nil repeats:NO];
            [[NSRunLoop mainRunLoop] addTimer:timer forMode:NSRunLoopCommonModes];;

            if(self.cha <=){

                // 时间过了就不处理接口返回的数据了
                return ;
            }

            if (!isExist) {//目录不存在(第一次从网络上直接获取图片)
                // 通知更改主题
                [[NSNotificationCenter defaultCenter] postNotificationName:@"change" object:self userInfo:@{@"info":self.models}];

                // 将图片  写入本地缓存起来，第二次就不用从网络上获取
                [self writeFileToCache];

                NSMutableArray *imgs = [NSMutableArray array];
                NSMutableArray *selImgs = [NSMutableArray array];

                for (XWMainBtnSkinModel *model in self.models) {
                    if ([model.type isEqualToString:@""]) {
                        [imgs addObject:model.img];
                        [selImgs addObject:model.selImg];
                    }
                }
                [self setUpTabbarWithImgs:imgs selImgs:selImgs isNet:YES];
                [self.view setNeedsLayout];
            }

        }else { // 如果没有请求到数据，就删除网络数据
            [self returnSkan];
        }

    } failedBlock:^(id error) {
        [SVProgressHUD showErrorWithStatus:error];
    }];

// 到时间后，就换回之前的皮肤
- (void)returnSkan
{
    if ([[NSFileManager defaultManager] fileExistsAtPath:self.fileCache]) {

        // 删除沙盒的数据
        [[NSFileManager defaultManager] removeItemAtPath:self.fileCache error:NULL];
    }
    // 该切回之前的主题了
    [[NSNotificationCenter defaultCenter] postNotificationName:@"cha" object:self userInfo:nil];

    NSMutableArray *normalImgs = [NSMutableArray arrayWithArray:@[@"img_btn_mainpage_normal.png",@"img_btn_class_normal",@"img_btn_theme",@"img_btn_message_normal",@"img_btn_me_normal"]];
    NSMutableArray *selImgs = [NSMutableArray arrayWithArray:@[@"img_btn_mainpage_select.png",@"img_btn_class_select",@"img_btn_theme",@"img_btn_message_select",@"img_btn_me_select"]];

    [self setUpTabbarWithImgs:normalImgs selImgs:selImgs isNet:NO];
}