我的购物清单项目Quantity TextField允许小数点，如果用户键入小数作为第一个字符，如".42"，则在下面的代码中将TextField字符串转换为Double时，它会抛出NumberFormatException。为了防止出现异常，我只需检查TextField值是否为"."。如果是，我将Quantity设置为空字符串，并显示一条Toast消息，告诉用户输入一个有效的数量，但它没有将Quantity状态设置为""，并且此时按下十进制键不显示Toast消息。我必须按退格键并再次按小数键才能显示消息。我该如何修复此问题？

• • 购物清单项目模型**

@Parcelize
data class ShoppingListItem(
    val id: Long = 0L,
    val shoppingListId: Long = 0L,
    ...
    val quantity: String = "",
): Parcelable

• • 视图模型**

private val _shoppingListItemState = MutableLiveData(
    savedStateHandle.get<ShoppingListItem>("shoppinglistitem")
        ?: ShoppingListItem()
)

override val shoppingListItemState: LiveData<ShoppingListItem>
    get() = _shoppingListItemState

...

override fun setStateValue(stateToEdit: String, stateValue: Any?) {
 when (stateToEdit) {
      ITEM_QUANTITY_STR -> {
          _shoppingListItemState.value =
          _shoppingListItemState.value!!.copy(quantity = stateValue.toString())
        } 
    }
}

• • 可组合**

CustomOutlinedTextField(
    fieldModifier = Modifier
        .width(150.dp)
        .padding(end = 8.dp)
        .onPreviewKeyEvent {
            if (it.key == Key.Tab && it.nativeKeyEvent.action == ACTION_DOWN) {
                focusManager.moveFocus(FocusDirection.Right)
                true
            } else {
                false
            }
        },
    label = ITEM_QUANTITY_STR,
    inputVal = shoppingListItemState.value!!.quantity,
    isSingleLine = true,
    keyboardOptions = KeyboardOptions.Default.copy(
        capitalization = KeyboardCapitalization.None,
        autoCorrect = false,
        keyboardType = KeyboardType.Decimal,
        imeAction = ImeAction.Next
    ),
    keyboardActions = KeyboardActions(
        onNext = { focusManager.moveFocus(FocusDirection.Right) }
    )
) { value ->
    if(value == ".") {
        Toast.makeText(context, "Please enter a valid quantity", Toast.LENGTH_LONG)
            .show()
        mainViewModel.setStateValue(
            ITEM_QUANTITY_STR,
            ""
        )
    } else {
        if (value.isEmpty()) {
        mainViewModel.setStateValue(
            ITEM_QUANTITY_STR,
            ""
        )
    } else {
            val counter = value.count { it == decimalSeparator }
            if (counter <= 1) {
                if (value.toDouble() <= 999_999.999) {
                    mainViewModel.setStateValue(
                        ITEM_QUANTITY_STR,
                        value
                    )
                }
            }
        }
    }
}