android - Jetpack Compose：使用 Coil 完成图像加载后获取回调

Question

我正在使用for加载一个非常大的资源图像，加载需要几十毫秒，第一次加载屏幕时甚至需要数百毫秒。如果图像尚未加载，我不想显示屏幕的某些部分。我徘徊在该方法的实现中，但找不到可以帮助我的东西。CoilJetpack ComposerememberImagePainter

Answer 1

您可以通过使用来实现此行为painter.state

val painter = rememberImagePainter(.....)

val painterState = painter.state

现在您可以非常轻松地比较线圈状态，如错误、加载和成功

if (painterState is ImagePainter.State.Loading) {
showLoadingDialog()
}

if(painterState is ImagePainter.State.Success) {
showContent()
}

Answer 2

有一个选项可以在构建器中传递一个监听器：

rememberImagePainter(data = "url or something", builder = {
    listener(object : ImageRequest.Listener {
        override fun onCancel(request: ImageRequest) {
            ...
        }

        override fun onError(request: ImageRequest, throwable: Throwable) {
            ...
        }

        override fun onStart(request: ImageRequest) {
            ...
        }

        override fun onSuccess(request: ImageRequest, metadata: ImageResult.Metadata) {
            ...
        }
    })
})

但是，如果您只想显示占位符图像，最简单的方法是使用placeholder(...)构建器中也提供的选项：

rememberImagePainter(data = "url or something", builder = {
    placeholder(R.drawable.image_placeholder)
})