Kotlin 协程的现有 3 函数回调 [英] Existing 3-function callback to Kotlin Coroutines
问题描述
我有一个带有具体示例的一般性问题:我想在拍照时使用 Kotlin 协程魔法而不是 Android 中的回调地狱.
I have a general question with a specific example: I'd like to use Kotlin coroutine magic instead of callback hell in Android when taking a picture.
manager.openCamera(cameraId, object : CameraDevice.StateCallback() {
override fun onOpened(openedCameraDevice: CameraDevice) {
println("Camera onOpened")
// even more callbacks with openedCameraDevice.createCaptureRequest()....
}
override fun onDisconnected(cameraDevice: CameraDevice) {
println("Camera onDisconnected")
cameraDevice.close()
}
...
我如何将其转换为不那么难看的东西?是否可以通过将主要流程指定为 promise-result 路径来获取具有三个左右函数的平均回调,并将其变成一个 promise-chain?如果那么,我应该/应该使用协程使其异步吗?
How would I convert that to something less ugly? Is it possible to take an average callback with three or so functions, and turn it into a promise-chain by designating the primary flow as the promise-result path? And if so, should/do I use coroutines to make it async?
我喜欢带有 async 和 .await 的东西,这会导致
I'd love something with async and .await that would result in
manager.open(cameraId).await().createCaptureRequest()
我正在尝试通过类似以下的方法来完成它,但我认为我没有使用 CompletableDeferred
对!
I'm trying to do it through something like the following, but I don't think I'm using CompletableDeferred
right!
suspend fun CameraManager.open(cameraId:String): CameraDevice {
val response = CompletableDeferred<CameraDevice>()
this.openCamera(cameraId, object : CameraDevice.StateCallback() {
override fun onOpened(cameraDevice: CameraDevice) {
println("camera onOpened $cameraDevice")
response.complete(cameraDevice)
}
override fun onDisconnected(cameraDevice: CameraDevice) {
response.completeExceptionally(Exception("Camera onDisconnected $cameraDevice"))
cameraDevice.close()
}
override fun onError(cameraDevice: CameraDevice, error: Int) {
response.completeExceptionally(Exception("Camera onError $cameraDevice $error"))
cameraDevice.close()
}
}, Handler())
return response.await()
}
推荐答案
在这种特殊情况下,您可以使用通用方法通过 suspendCoroutine
函数将基于回调的 API 转换为挂起函数:
In this particular case you can use a general approach to convert a callback-based API to a suspending function via suspendCoroutine
function:
suspend fun CameraManager.openCamera(cameraId: String): CameraDevice? =
suspendCoroutine { cont ->
val callback = object : CameraDevice.StateCallback() {
override fun onOpened(camera: CameraDevice) {
cont.resume(camera)
}
override fun onDisconnected(camera: CameraDevice) {
cont.resume(null)
}
override fun onError(camera: CameraDevice, error: Int) {
// assuming that we don't care about the error in this example
cont.resume(null)
}
}
openCamera(cameraId, callback, null)
}
现在,在您的应用程序代码中,您只需执行 manager.openCamera(cameraId)
并获取对 CameraDevice
的引用(如果它已成功打开或 null<)/code> 如果不是.
Now, in your application code you can just do manager.openCamera(cameraId)
and get a reference to CameraDevice
if it was opened successfully or null
if it was not.
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