InputTransformation

BasicTextFieldCustomInputTransformationSample

@Composable
fun BasicTextFieldCustomInputTransformationSample() {
    // Demonstrates how to create a custom and relatively complex InputTransformation.
    val state = remember { TextFieldState() }
    BasicTextField(
        state,
        inputTransformation =
            InputTransformation {
                // A filter that always places newly-input text at the start of the string, after a
                // prompt character, like a shell.
                val promptChar = '>'
                fun CharSequence.countPrefix(char: Char): Int {
                    var i = 0
                    while (i < length && get(i) == char) i++
                    return i
                }
                // Step one: Figure out the insertion point.
                val newPromptChars = asCharSequence().countPrefix(promptChar)
                val insertionPoint = if (newPromptChars == 0) 0 else 1
                // Step two: Ensure text is placed at the insertion point.
                if (changes.changeCount == 1) {
                    val insertedRange = changes.getRange(0)
                    val replacedRange = changes.getOriginalRange(0)
                    if (!replacedRange.collapsed && insertedRange.collapsed) {
                        // Text was deleted, delete forwards from insertion point.
                        delete(insertionPoint, insertionPoint + replacedRange.length)
                    }
                }
                // Else text was replaced or there were multiple changes - don't handle.
                // Step three: Ensure the prompt character is there.
                if (newPromptChars == 0) {
                    insert(0, ">")
                }
                // Step four: Ensure the cursor is ready for the next input.
                placeCursorAfterCharAt(0)
            },
    )
}