ios 异步和多线程

    //display&data
    _myview.view_searchbar.btn_back.hidden=true;
    [LSJsonHelper PrintLog:@"viewdidload"];
    [LSJsonHelper RequestHttp:gbl_urlindexcategory handle:^(NSDictionary *data) {
        [LSJsonHelper PrintLog:@"callback"];
        _data_category=[LSJsonHelper ConverJason2Model:data cc:[LSModel_VCategory_All class] isArray:YES];
        NSString *img1=[NSString stringWithFormat:@"%@%@",gbl_imgspath,_data_category[0].cg_pic];
        [LSJsonHelper PrintLog:@"before request img"];
        
        dispatch_async(dispatch_get_main_queue(), ^{
            [LSNSURL LoadImageForimg:img1 img:_myview.image_eat];
            [LSJsonHelper PrintLog:@"after set img to imagevie"];
        });
        
        [LSJsonHelper PrintLog:@"end this function"];
    }];

2018-07-02 17:22:12.302 MyCity100[3014:82518] 2018-07-02 05:22:12:301.<NSThread: 0x7b771880>{number = 1, name = main} :viewdidload
2018-07-02 17:22:12.309 MyCity100[3014:82518] 2018-07-02 05:22:12:309.<NSThread: 0x7b771880>{number = 1, name = main} :viewWillAppear
2018-07-02 17:22:12.354 MyCity100[3014:82518] 2018-07-02 05:22:12:355.<NSThread: 0x7b771880>{number = 1, name = main} :viewDidAppear
2018-07-02 17:22:12.431 MyCity100[3014:82573] 2018-07-02 05:22:12:431.<NSThread: 0x7c98ed90>{number = 3, name = (null)} :callback
2018-07-02 17:22:12.436 MyCity100[3014:82573] 2018-07-02 05:22:12:436.<NSThread: 0x7c98ed90>{number = 3, name = (null)} :before request img
2018-07-02 17:22:12.437 MyCity100[3014:82573] 2018-07-02 05:22:12:437.<NSThread: 0x7c98ed90>{number = 3, name = (null)} :end this function
2018-07-02 17:22:15.616 MyCity100[3014:82518] 2018-07-02 05:22:15:616.<NSThread: 0x7b771880>{number = 1, name = main} :after set img to imagevie

可以看到。异步网络请求后的回调函数是在子线程中执行。

所以时间上一般页面执行完了显示函数，才会执行回调。

更主要的是页面上的控件都是在主线程上创建的。基本所有语言都是要求由主线程进行刷新。

oc 也不例外，所以编写主线程的回调函数。

 dispatch_async(dispatch_get_main_queue(), ^{

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