android - 等待我的代码完成使用Kotlin从API调用中获取所有信息

Question

嗨，我是Kotlin的新手

我正在尝试编写以下代码-

private fun syncLocalCartItemsToNetwork(tokenObject: MyVerteUserAuthTokenObject) {
        val failedSyncedProducts: MutableList<String> = mutableListOf()


        locallySavedCartModels.forEach { //I need to make the code wait until all callbacks from this loop finishes
            ShoppingCartUtils.addItemToCart(tokenObject.token, it, this@ShoppingCartActivity, object : ShoppingCartUtils.OnMyVerteCartProductsSyncListener {
                override fun onProductSyncFailed(productID: String) {
                    failedSyncedProducts.add(productID)
                }
            })
        }

        if (failedSyncedProducts.isNotEmpty()) {
            val builder = AlertDialog.Builder(this)
            builder.setTitle("Shopping Cart was not fully synced")
            builder.setMessage("The following items were not synced well due to stock availability, please re add them - \n\n" +
                    "${failedSyncedProducts.forEach { it + "\n\n" }}")
            builder.setPositiveButton("Confirm") { dialog, _ ->
                dialog.dismiss()
            }
            val dialog: AlertDialog = builder.create()
            dialog.show()
        }
        Toast.makeText(this@ShoppingCartActivity, "finished", Toast.LENGTH_SHORT).show()


    }

如您所见，我正在遍历所有 locallySavedCartModels并可能从中获得结果。

我需要的选项是使功能等待，直到所有回调都从forEach循环中完成，然后才继续执行我的代码以检查我的String列表是否为空。

如何使用Kotlin做到这一点？

Answer 1

使用协程可能是最干净的方法，但这意味着重写ShoppingCartUtils以使用暂停函数而不是回调。

要使用现有的代码，一种方法可能是创建一个类，该类在被调用足够多的时间后执行剩余的代码，如下所示:

class CallbackAggregator(val count: Int) {
    var finalCallback: (() -> Unit)? = null
    private var calls = 0

    fun increment() {
        if (++calls == count)
            finalCallback?.invoke()
    }
}

用法:

private fun syncLocalCartItemsToNetwork(tokenObject: MyVerteUserAuthTokenObject) {
    val failedSyncedProducts: MutableList<String> = mutableListOf()

    val aggregator = CallbackAggregator(locallySavedCartModels.size)

    locallySavedCartModels.forEach { 
        ShoppingCartUtils.addItemToCart(tokenObject.token, it, this@ShoppingCartActivity, object : ShoppingCartUtils.OnMyVerteCartProductsSyncListener {
                override fun onProductSyncFailed(productID: String) {
                    failedSyncedProducts.add(productID)
                    aggregator.increment()
                }
            })
        }

    aggregator.finalCallback = {
        if (failedSyncedProducts.isNotEmpty()) {
            AlertDialog.Builder(this@ShoppingCartActivity).apply {
                title = "Shopping Cart was not fully synced"
                message = "The following items were not synced well due to stock availability, please re add them - \n\n" +
                    "${failedSyncedProducts.joinToString("\n\n")}")
                setPositiveButton("Confirm") { dialog, _ ->
                    dialog.dismiss()
                }
                create().show()
            }
        }
        Toast.makeText(this@ShoppingCartActivity, "finished", Toast.LENGTH_SHORT).show()
    }
}