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@benjaminsnorris
Last active June 9, 2022 08:28
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Live reload of text in UITextView while preserving cursor position and text selection
import UIKit
class TextEditing: UIViewController {
@IBOutlet weak var textView: UITextView?
func updateText(with newString: String?) {
guard let textView = textView, newString = newString, (diffRange, changedText) = diff(textView.text, newString) else { return }
guard let selectedRange = textView.selectedTextRange else { textView.text = newString; return }
textView.text = newString
let cursorOffset = textView.offsetFromPosition(textView.beginningOfDocument, toPosition: selectedRange.start)
let selectedEndOffset = textView.offsetFromPosition(textView.beginningOfDocument, toPosition: selectedRange.end)
let selectedRangeLength = selectedEndOffset - cursorOffset
if selectedEndOffset < diffRange.startIndex {
// Change is after current cursor
moveCursorRelativeToBeginning(with: cursorOffset, rangeLength: selectedRangeLength)
} else if cursorOffset < diffRange.startIndex && selectedEndOffset > diffRange.endIndex {
// Change occurs within selection
moveCursorRelativeToBeginning(with: cursorOffset, rangeLength: selectedRangeLength + changedText.characters.count - diffRange.count)
} else if cursorOffset >= diffRange.endIndex {
// Change occurs completely before current cursor
moveCursorRelativeToBeginning(with: cursorOffset + changedText.characters.count - diffRange.count, rangeLength: selectedRangeLength)
} else if diffRange.startIndex < selectedEndOffset && diffRange.startIndex > cursorOffset {
// Change starts in middle of selection
moveCursorRelativeToBeginning(with: cursorOffset, rangeLength: selectedRangeLength - (selectedEndOffset - diffRange.startIndex))
} else if diffRange.startIndex <= cursorOffset && cursorOffset < diffRange.endIndex {
// Change is a removal/change over the current cursor position
let rangeLength = selectedRangeLength - (diffRange.endIndex - cursorOffset)
moveCursorRelativeToBeginning(with: cursorOffset - (cursorOffset - diffRange.startIndex) + changedText.characters.count, rangeLength: rangeLength > 0 ? rangeLength : 0)
}
}
private func moveCursorRelativeToBeginning(with offset: Int, rangeLength: Int = 0) {
guard let textView = textView, startPosition = textView.positionFromPosition(textView.beginningOfDocument, offset: offset), endPosition = textView.positionFromPosition(startPosition, offset: rangeLength) else { return }
textView.selectedTextRange = textView.textRangeFromPosition(startPosition, toPosition: endPosition)
}
}
import XCTest
import Nimble
import Diff
@testable import align
class TextEditingSpec: XCTestCase {
var textEditing: TextEditing!
override func setUp() {
super.setUp()
textEditing = TextEditing.initializeFromStoryboard()
let _ = textEditing.view
textEditing.textView = UITextView()
}
/// test that it loads properly
func testThatItLoadsProperly() {
expect(self.textEditing.textView).toNot(beNil())
expect(self.textEditing.textView?.text) == ""
expect(self.textEditing.title).to(beNil())
}
// MARK: - Cursor position tests
// Original text: "Watch Bugger attack videos together and discuss strategy."
/// test that cursor position does not change if state changes but agenda is unchanged
func testThatCursorPositionDoesNotChangeIfStateChangesButAgendaIsUnchanged() {
textEditing.textView?.text = "Watch Bugger attack videos together and discuss strategy."
textEditing.textView?.becomeFirstResponder()
moveCursorRelativeToBeginning(with: 10)
expect(self.cursorOffset()) == 10
expect(self.selectedRangeLength()) == 0
textEditing.updateText(with: "Watch Bugger attack videos together and discuss strategy.")
expect(self.cursorOffset()) == 10
expect(self.selectedRangeLength()) == 0
}
/// test that cursor position does not change when agenda has changes after cursor
func testThatCursorPositionDoesNotChangeWhenAgendaHasChangesAfterCursor() {
textEditing.textView?.text = "Watch Bugger attack videos together and discuss strategy."
textEditing.textView?.becomeFirstResponder()
moveCursorRelativeToBeginning(with: 10)
expect(self.cursorOffset()) == 10
expect(self.selectedRangeLength()) == 0
textEditing.updateText(with: "Watch Bugger attack videos together.")
expect(self.cursorOffset()) == 10
expect(self.selectedRangeLength()) == 0
}
/// test that cursor position changes when agenda has removed text before current cursor position
func testThatCursorPositionChangesWhenAgendaHasRemovedTextBeforeCurrentCursorPosition() {
textEditing.textView?.text = "Watch Bugger attack videos together and discuss strategy."
textEditing.textView?.becomeFirstResponder()
moveCursorRelativeToBeginning(with: 10)
expect(self.cursorOffset()) == 10
expect(self.selectedRangeLength()) == 0
textEditing.updateText(with: "Bugger attack videos together and discuss strategy.")
expect(self.cursorOffset()) == 4
expect(self.selectedRangeLength()) == 0
}
/// test that cursor position changes when agenda has changed text before current cursor position
func testThatCursorPositionChangesWhenAgendaHasChangedTextBeforeCurrentCursorPosition() {
textEditing.textView?.text = "Watch Bugger attack videos together and discuss strategy."
textEditing.textView?.becomeFirstResponder()
moveCursorRelativeToBeginning(with: 10)
expect(self.cursorOffset()) == 10
expect(self.selectedRangeLength()) == 0
textEditing.updateText(with: "View Bugger attack videos together and discuss strategy.")
expect(self.cursorOffset()) == 9
expect(self.selectedRangeLength()) == 0
}
/// test that cursor position changes when agenda has removed text that includes current cursor position
func testThatCursorPositionChangesWhenAgendaHasRemovedTextThatIncludesCurrentCursorPosition() {
textEditing.textView?.text = "Watch Bugger attack videos together and discuss strategy."
textEditing.textView?.becomeFirstResponder()
moveCursorRelativeToBeginning(with: 10)
expect(self.cursorOffset()) == 10
expect(self.selectedRangeLength()) == 0
textEditing.updateText(with: "Watch attack videos together and discuss strategy.")
expect(self.cursorOffset()) == 6
expect(self.selectedRangeLength()) == 0
}
/// test that cursor position changes when agenda has changed text that includes current cursor position
func testThatCursorPositionChangesWhenAgendaHasChangedTextThatIncludesCurrentCursorPosition() {
textEditing.textView?.text = "Watch Bugger attack videos together and discuss strategy."
textEditing.textView?.becomeFirstResponder()
moveCursorRelativeToBeginning(with: 10)
expect(self.cursorOffset()) == 10
expect(self.selectedRangeLength()) == 0
textEditing.updateText(with: "View recorded Bugger attack videos together and discuss strategy.")
expect(self.cursorOffset()) == 18
expect(self.selectedRangeLength()) == 0
}
// MARK: - Selected text tests
/// test that text selection does not changes when text does not change
func testThatTextSelectionDoesNotChangesWhenTextDoesNotChange() {
textEditing.textView?.text = "Watch Bugger attack videos together and discuss strategy."
textEditing.textView?.becomeFirstResponder()
moveCursorRelativeToBeginning(with: 6, length: 6)
expect(self.cursorOffset()) == 6
expect(self.selectedRangeLength()) == 6
textEditing.updateText(with: "Watch Bugger attack videos together and discuss strategy.")
expect(self.cursorOffset()) == 6
expect(self.selectedRangeLength()) == 6
}
/// test that text selection does not change when text changes occur after selection
func testThatTextSelectionDoesNotChangeWhenTextChangesOccurAfterSelection() {
textEditing.textView?.text = "Watch Bugger attack videos together and discuss strategy."
textEditing.textView?.becomeFirstResponder()
moveCursorRelativeToBeginning(with: 6, length: 6)
expect(self.cursorOffset()) == 6
expect(self.selectedRangeLength()) == 6
textEditing.updateText(with: "Watch Bugger attack videos and discuss strategy.")
expect(self.cursorOffset()) == 6
expect(self.selectedRangeLength()) == 6
}
/// test that text selection remains same but moves when text is added before selection
func testThatTextSelectionRemainsSameButMovesWhenTextIsAddedBeforeSelection() {
textEditing.textView?.text = "Watch Bugger attack videos together and discuss strategy."
textEditing.textView?.becomeFirstResponder()
moveCursorRelativeToBeginning(with: 6, length: 6)
expect(self.cursorOffset()) == 6
expect(self.selectedRangeLength()) == 6
textEditing.updateText(with: "Watch the Bugger attack videos together and discuss strategy.")
expect(self.cursorOffset()) == 10
expect(self.selectedRangeLength()) == 6
}
/// test that text selection adjusts to include changes that occur within the selection
func testThatTextSelectionAdjustsToIncludeChangesThatOccurWithinTheSelection() {
textEditing.textView?.text = "Watch Bugger attack videos together and discuss strategy."
textEditing.textView?.becomeFirstResponder()
moveCursorRelativeToBeginning(with: 6, length: 6)
expect(self.cursorOffset()) == 6
expect(self.selectedRangeLength()) == 6
textEditing.updateText(with: "Watch Bear attack videos together and discuss strategy.")
expect(self.cursorOffset()) == 6
expect(self.selectedRangeLength()) == 4
}
/// test that text selection expands to include additions that occur within the selection
func testThatTextSelectionExpandsToIncludeAdditionsThatOccurWithinTheSelection() {
textEditing.textView?.text = "Watch Bugger attack videos together and discuss strategy."
textEditing.textView?.becomeFirstResponder()
moveCursorRelativeToBeginning(with: 6, length: 6)
expect(self.cursorOffset()) == 6
expect(self.selectedRangeLength()) == 6
textEditing.updateText(with: "Watch Big bad bugger attack videos together and discuss strategy.")
expect(self.cursorOffset()) == 6
expect(self.selectedRangeLength()) == 14
}
/// test that text selection is truncated when the end of the selection is removed
func testThatTextSelectionIsTruncatedWhenTheEndOfTheSelectionIsRemoved() {
textEditing.textView?.text = "Watch Bugger attack videos together and discuss strategy."
textEditing.textView?.becomeFirstResponder()
moveCursorRelativeToBeginning(with: 6, length: 6)
expect(self.cursorOffset()) == 6
expect(self.selectedRangeLength()) == 6
textEditing.updateText(with: "Watch Bug attack videos together and discuss strategy.")
expect(self.cursorOffset()) == 6
expect(self.selectedRangeLength()) == 3
}
/// test that text selection is truncated when the end of the selection is changed
func testThatTextSelectionIsTruncatedWhenTheEndOfTheSelectionIsChanged() {
textEditing.textView?.text = "Watch Bugger attack videos together and discuss strategy."
textEditing.textView?.becomeFirstResponder()
moveCursorRelativeToBeginning(with: 6, length: 6)
expect(self.cursorOffset()) == 6
expect(self.selectedRangeLength()) == 6
textEditing.updateText(with: "Watch Bug vehicle attack videos together and discuss strategy.")
expect(self.cursorOffset()) == 6
expect(self.selectedRangeLength()) == 3
}
/// test that text selection is truncated when the beginning of the selection is removed
func testThatTextSelectionIsTruncatedWhenTheBeginningOfTheSelectionIsRemoved() {
textEditing.textView?.text = "Watch Bugger attack videos together and discuss strategy."
textEditing.textView?.becomeFirstResponder()
moveCursorRelativeToBeginning(with: 6, length: 6)
expect(self.cursorOffset()) == 6
expect(self.selectedRangeLength()) == 6
textEditing.updateText(with: "Watch er attack videos together and discuss strategy.")
expect(self.cursorOffset()) == 6
expect(self.selectedRangeLength()) == 2
}
/// test that text selection is truncated and moved when the beginning of the selection is changed
func testThatTextSelectionIsTruncatedAndMovedWhenTheBeginningOfTheSelectionIsChanged() {
textEditing.textView?.text = "Watch Bugger attack videos together and discuss strategy."
textEditing.textView?.becomeFirstResponder()
moveCursorRelativeToBeginning(with: 6, length: 6)
expect(self.cursorOffset()) == 6
expect(self.selectedRangeLength()) == 6
textEditing.updateText(with: "Watching some tiger attack videos together and discuss strategy.")
expect(self.cursorOffset()) == 16
expect(self.selectedRangeLength()) == 3
}
/// test that cursor does not move when the exact selection is removed
func testThatCursorDoesNotMoveWhenTheExactSelectionIsRemoved() {
textEditing.textView?.text = "Watch Bugger attack videos together and discuss strategy."
textEditing.textView?.becomeFirstResponder()
moveCursorRelativeToBeginning(with: 6, length: 6)
expect(self.cursorOffset()) == 6
expect(self.selectedRangeLength()) == 6
textEditing.updateText(with: "Watch attack videos together and discuss strategy.")
expect(self.cursorOffset()) == 6
expect(self.selectedRangeLength()) == 0
}
/// test that cursor is moved when entire selection is removed
func testThatCursorIsMovedWhenEntireSelectionIsRemoved() {
textEditing.textView?.text = "Watch Bugger attack videos together and discuss strategy."
textEditing.textView?.becomeFirstResponder()
moveCursorRelativeToBeginning(with: 6, length: 6)
expect(self.cursorOffset()) == 6
expect(self.selectedRangeLength()) == 6
textEditing.updateText(with: "Wattack videos together and discuss strategy.")
expect(self.cursorOffset()) == 3
expect(self.selectedRangeLength()) == 0
}
/// test that cursor is moved when entire selection is changed
func testThatCursorIsMovedWhenEntireSelectionIsChanged() {
textEditing.textView?.text = "Watch Bugger attack videos together and discuss strategy."
textEditing.textView?.becomeFirstResponder()
moveCursorRelativeToBeginning(with: 6, length: 6)
expect(self.cursorOffset()) == 6
expect(self.selectedRangeLength()) == 6
textEditing.updateText(with: "Watching attack videos together and discuss strategy.")
expect(self.cursorOffset()) == 8
expect(self.selectedRangeLength()) == 0
}
}
// MARK: - Private functions
private extension TextEditingSpec {
private func cursorOffset() -> Int {
guard let textView = textEditing.textView, selectedRange = textView.selectedTextRange else { return 0 }
return textView.offsetFromPosition(textView.beginningOfDocument, toPosition: selectedRange.start)
}
private func selectedRangeLength() -> Int {
guard let textView = textEditing.textView, selectedRange = textView.selectedTextRange else { return 0 }
return textView.offsetFromPosition(textView.beginningOfDocument, toPosition: selectedRange.end) - cursorOffset()
}
private func moveCursorRelativeToBeginning(with offset: Int, length: Int = 0) {
guard let textView = textEditing.textView, startPosition = textView.positionFromPosition(textView.beginningOfDocument, offset: offset), endPosition = textView.positionFromPosition(startPosition, offset: length) else { return }
textView.selectedTextRange = textView.textRangeFromPosition(startPosition, toPosition: endPosition)
}
}
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