fun createCoroutineTest(){
        suspend {
            //val foo=foo()
            try {
                val name = getMessageFromNetwork()
                Toast.makeText(App.instance.applicationContext,name,Toast.LENGTH_SHORT).show()
                //System.err: java.lang.RuntimeException: Can't toast on a thread that has not called Looper.prepare()
            }catch (e:Exception){
                e.printStackTrace()
                //Toast.makeText(App.instance.applicationContext,"success",Toast.LENGTH_SHORT).show()
            }
        }.createCoroutine(object : Continuation<Unit>{
            override val context=EmptyCoroutineContext
            override fun resumeWith(result: Result<Unit>) {
                Log.d("TAG","Coroutine End with${result}")
                //Toast.makeText(App.instance.applicationContext,"$result",Toast.LENGTH_SHORT).show()
                // Caused by: java.lang.RuntimeException: Can't toast on a thread that has not called Looper.prepare()
            }
        }).resume(Unit)
        //调用协程就能启动协程了
    }

/**
     * 从服务器取信息
     */
    private suspend fun getMessageFromNetwork(): String {
        var name = ""
        withContext(Dispatchers.IO) {
            delay(3000)
            name = "success"
        }
        if (""==name){
            throw IllegalArgumentException("加载失败啦")
        }
        return name
    }

使用 suspend {}.resume() suspend {}.startCoroutine{}两种方式启动协程，suspend {} 和resumeWith(result: Result) {}里面都是子线程，怎么把结果切回主线程上面呢？