Add SelectionMode which doesn't allow unselecting a date

[CmdrSharp]

Hi! Thanks again for a great project :)

It would be nice to have a SelectionMode where a selection is always made (so basically the Single selection date, without the ability to UNSELECT a date).

One way to implement this now is by creating a custom day component where you simply don't react in the onClick-event if the click is on the current day, like so:

    Card(
        modifier = modifier.aspectRatio(1f).padding(2.dp),
        elevation = if (state.isFromCurrentMonth) 4.dp else 0.dp,
        border = if (state.isCurrentDay) BorderStroke(1.dp, MaterialTheme.colors.primary) else null,
        contentColor = if (isSelected) MaterialTheme.colors.secondary else contentColorFor(
            backgroundColor = MaterialTheme.colors.surface
        )
    ) {
        Box(
            modifier = Modifier.pointerInput(Unit) {
                detectTapGestures(
                    onLongPress = {
                        onLongPress(date)
                    },
                    onTap = {
                        if(!state.selectionState.isDateSelected(date)) {
                            onClick(date)
                            selectionState.onDateSelected(date)
                        }
                    }
                )
            },
            contentAlignment = Alignment.Center,
        ) {
            Text(
                text = date.dayOfMonth.toString(),
                fontWeight = textFontWeight
            )
        }
    }

[boguszpawlowski]

@CmdrSharp Hello! You can easily implement it on your side, a quick POC would be:

@Immutable
public class LockedSelectionState(
  initialSelection: LocalDate,
) : SelectionState {
  private var _selection by mutableStateOf(initialSelection)

  override fun isDateSelected(date: LocalDate): Boolean = date == _selection

  override fun onDateSelected(date: LocalDate) {
    when (date == _selection) {
      true -> Unit
      false -> _selection = date
    }
  }
}

Let me know if this satisfies your use-case!

[CmdrSharp]

@boguszpawlowski Seems like a reasonable solution - I came up with another one, as I show in the post - but I still think it might make a good native addition to the library. Based on the current options, it seems to make sense :)

[boguszpawlowski]

@CmdrSharp I think it's too specific for an addition to the library itself. It has a limited amount of native selection state-s by a design, as they are easily extensible and the larger amount of options would introduce more confusion then benefits. But actually, I think there is a middle ground -> we could modify the onSelectionChange callback in the DynamicSelectionState to resemble confirmStateChange from SwipeableState. So basically, you would be able to block state change if it wouldn't suit you -> e.g. when you don't want to unselect the date. Quick POC:

@Stable
public class DynamicSelectionState(
  private val confirmSelectionChange: (List<LocalDate>) -> Boolean = { true },
  selection: List<LocalDate>,
  selectionMode: SelectionMode,
) : SelectionState {

  private var _selection by mutableStateOf(selection)
  private var _selectionMode by mutableStateOf(selectionMode)

  public var selection: List<LocalDate>
    get() = _selection
    set(value) {
      if (value != selection && confirmSelectionChange(value)) {
        _selection = value
      }
    }

What do you think?

[boguszpawlowski]

The reference to the SwipableState: https://developer.android.com/reference/kotlin/androidx/compose/material/SwipeableState#SwipeableState(kotlin.Any,androidx.compose.animation.core.AnimationSpec,kotlin.Function1)

[CmdrSharp]

That seems like a reasonable implementation!