按顺序执行Dispatch main

Question

如何按顺序执行一组调度代码。例如：

Dispatch.main.async{
 //call API, it may takes 5-10 seconds..
 //do something..
   print("done 1")
}

Dispatch.main.async{
//call API, it may takes 5-10 seconds..
//do something
  print("done 2")
}

Dispatch.main.asyncAfter{
  print("completed")
}

Output:
 completed
 done1
 done2

Expected output:
 done1
 done2
 completed

我使用main是因为“做点什么”就是填充resut to UI。我试着使用global()，但“completed”总是首先执行，而且不适合使用分派时间延迟，因为不能确定API调用时间有多长。需要在swift中提出建议~

Answer 1

 DispatchQueue.main.async{
            //call API, it may takes 5-10 seconds..
            //do something..
            print("done 1")
        }

        DispatchQueue.main.async{
            //call API, it may takes 5-10 seconds..
            //do something
            print("done 2")
        }

        DispatchQueue.main.asyncAfter(deadline: .now() + 0.1){
            print("completed")
        }

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