Jetpack Compose:从 Composable 函数启动 ActivityResultContract 请求 [英] Jetpack Compose: Launch ActivityResultContract request from Composable function

问题描述

截至 1.2.0-beta01androidx.activity:activity-ktx，不能再launch使用Activity.registerForActivityResult()创建的请求，如上面链接中突出显示的在行为改变"下并在 此处的 Google 问题中看到.

As of 1.2.0-beta01 of androidx.activity:activity-ktx, one can no longer launch the request created using Activity.registerForActivityResult(), as highlighted in the above link under "Behavior Changes" and seen in the Google issue here.

应用程序现在应该如何通过 @Composable 函数启动这个请求?以前，应用程序可以通过使用 Ambient 将 MainActivity 的实例沿链向下传递，然后轻松启动请求.

How should an application launch this request via a @Composable function now? Previously, an app could pass the instance of the MainActivity down the chain via using an Ambient and then launch the request easily.

可以通过以下方式解决新行为，例如，在活动的 onCreate 函数之外实例化后，将注册活动结果的类传递到链中，然后在可组合.但是，不能通过这种方式注册完成后执行的回调.

The new behavior can be worked around by, for example, passing a class registering for the activity result down the chain after being instantiated outside of the Activity's onCreate function, and then launch the request in a Composable. However, registering the a callback to be executed after completion cannot be done this way.

可以通过创建自定义 ActivityResultContract 来解决这个问题，它在启动时接受回调.但是，这意味着几乎没有任何内置 ActivityResultContracts 可以与 Jetpack Compose 一起使用.

One could get around this by creating custom ActivityResultContract, which, at launch, take a callback. However, this would mean that virtually none of the built-in ActivityResultContracts could be used with Jetpack Compose.

TL;DR

应用如何从 @Composable 函数启动 ActivityResultsContract 请求?

How would an app launch an ActivityResultsContract request from a @Composable function?

推荐答案

从 androidx.activity:activity-compose:1.3.0-alpha06 开始，registerForActivityResult() API 已重命名为 rememberLauncherForActivityResult() 以更好地表明返回的 ActivityResultLauncher 是代表您记住的托管对象.

As of androidx.activity:activity-compose:1.3.0-alpha06, the registerForActivityResult() API has been renamed to rememberLauncherForActivityResult() to better indicate the returned ActivityResultLauncher is a managed object that is remembered on your behalf.

val result = remember { mutableStateOf<Bitmap?>(null) }
val launcher = rememberLauncherForActivityResult(ActivityResultContracts.TakePicturePreview()) {
    result.value = it
}

Button(onClick = { launcher.launch() }) {
    Text(text = "Take a picture")
}

result.value?.let { image ->
    Image(image.asImageBitmap(), null, modifier = Modifier.fillMaxWidth())
}

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