TextFieldTextStyles

BasicTextFieldTrackedRangeToggleBoldSample

@Composable
fun BasicTextFieldTrackedRangeToggleBoldSample() {
    // This sample demonstrates a realistic rich-text editor scenario using the `TrackedRange` and
    // `TextFieldTextStyles` APIs. It implements a "Toggle Bold" formatting function on the current
    // selection.
    // For simplicity, this sample keeps bold styles non-overlapping and contiguous, assuming they
    // are
    // applied exclusively through this method.
    val state = rememberTextFieldState("Hello World")
    // This derived state calculates whether the current selection is completely covered by
    // bold text styles. This ensures the "Bold" toggle button accurately reflects the
    // state of the selected text.
    val isSelection100PercentBold by derivedStateOf {
        val selection = state.selection
        if (selection.collapsed) {
            false
        } else {
            val spanStyles = state.textStyles.getSpanStyles(selection.min, selection.max)
            var boldCoverage = 0
            for (style in spanStyles) {
                if (style.item.fontWeight == FontWeight.Bold) {
                    val overlapStart = maxOf(style.start, selection.min)
                    val overlapEnd = minOf(style.end, selection.max)
                    if (overlapEnd > overlapStart) {
                        boldCoverage += (overlapEnd - overlapStart)
                    }
                }
            }
            boldCoverage == selection.length
        }
    }
    fun TextFieldBuffer.unBoldSelection() {
        // Query existing bold styles in the selection
        val intersectingStyles =
            getSpanStyles(selection.min, selection.max).filter {
                it.spanStyle.fontWeight == FontWeight.Bold
            }
        // We modify or remove existing styles to exclude the selected range
        for (style in intersectingStyles) {
            val range = style.textRange
            if (range.start >= selection.min && range.end <= selection.max) {
                // The style is fully inside the selection. Remove it.
                removeStyle(style)
            } else if (range.start < selection.min && range.end > selection.max) {
                // The style completely covers the selection. We need to split it.
                val oldEnd = range.end
                // Truncate the start part
                style.textRange = TextRange(range.start, selection.min)
                // Add a new style for the end part
                addStyle(
                    SpanStyle(fontWeight = FontWeight.Bold),
                    TextRange(selection.max, oldEnd),
                    ExpandPolicy.AtEnd,
                )
            } else if (range.start < selection.min) {
                // The style overlaps with the start of the selection. Truncate it.
                style.textRange = TextRange(range.start, selection.min)
            } else {
                // The style overlaps with the end of the selection. Truncate it.
                style.textRange = TextRange(selection.max, range.end)
            }
        }
    }
    fun TextFieldBuffer.boldSelection() {
        // Query existing bold styles in the selection
        val intersectingStyles =
            getSpanStyles(selection.min, selection.max).filter {
                it.spanStyle.fontWeight == FontWeight.Bold
            }
        // To keep bold styles non-overlapping, we merge any intersecting bold
        // styles with the new selection range into a single contiguous bold style.
        var mergedStart = selection.min
        var mergedEnd = selection.max
        for (style in intersectingStyles) {
            mergedStart = minOf(mergedStart, style.textRange.start)
            mergedEnd = maxOf(mergedEnd, style.textRange.end)
            // Remove the fragmented style
            removeStyle(style)
        }
        addStyle(
            SpanStyle(fontWeight = FontWeight.Bold),
            TextRange(mergedStart, mergedEnd),
            ExpandPolicy.AtEnd,
        )
    }
    Column {
        Button(
            onClick = {
                state.edit {
                    val selection = this.selection
                    if (selection.collapsed) return@edit
                    if (isSelection100PercentBold) {
                        unBoldSelection()
                    } else {
                        boldSelection()
                    }
                }
            }
        ) {
            Text(
                "B",
                fontWeight = if (isSelection100PercentBold) FontWeight.Bold else FontWeight.Normal,
            )
        }
        BasicTextField(state = state, textStyle = LocalTextStyle.current)
    }
}