Coil Kotlin Uri to Bitmap 抛出空指针异常

Question

Trying to convert a Uri image file to Bitmap in Kotlin fails with a Null Pointer exception. How can I fix this?

var bitmap = remember {  mutableStateOf<Bitmap?>(null)}

LaunchedEffect(key1 = "tobitmap") {
    CoroutineScope(Dispatchers.IO).launch {
        bitmap.value = uriToBitmap(
            context,
            shoppingListScreenViewModel.state.value.imageUri
        )
    }
}

Image(
    bitmap = bitmap.value?.asImageBitmap()!!, //Throws exception here
    contentDescription = ""
)

private suspend fun uriToBitmap(context: Context, uri: Uri?): Bitmap {

    val loader = ImageLoader(context)
    val request = ImageRequest.Builder(context)
        .data(uri)
        .allowHardware(false) // Disable hardware bitmaps.
        .build()

    val result = (loader.execute(request) as SuccessResult).drawable
    val bitmap = (result as BitmapDrawable).bitmap

    val resizedBitmap = Bitmap.createScaledBitmap(
        bitmap, 80, 80, true);

    return resizedBitmap
}

Answer 1

var bitmap = remember {  mutableStateOf<Bitmap?>(null)}

Here, bitmap.value will be null .

Image(
    bitmap = bitmap.value?.asImageBitmap()!!, //Throws exception here
    contentDescription = ""
)

Here, bitmap.value?.asImageBitmap() will be null , since bitmap.value is null . As a result, you will crash with a NullPointerException as soon as you execute this code.

Eventually , bitmap.value will not be null , courtesy of your LaunchedEffect , but that will take some time. You need to rework your composable to be able to work prior to that point in time.

Answer 2

bitmap = bitmap.value?.asImageBitmap()!!, //Throws exception here

not-null assertion is not a good way to handle this.

Your possible options are either display Image with

bitmap?.value?.asImageBitmap()?.let{ imageBitmap->
   Image(...)
} 

and wait for bitmap to be created while you display nothing

or display preferably a Composable for loading or Image with placeholder.

if(bitmap.value!= null) {
  Image(...)
} else {
 // Your loading Composable
}

Another option is to use SubcomposeAsyncImage which has slots for Loading, Error and Success Composable slots so you can pass your Composables inside these slots.