57 lines
2.1 KiB
Swift
57 lines
2.1 KiB
Swift
//
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// Copyright (c) 2018 Open Whisper Systems. All rights reserved.
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//
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import Foundation
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import UIKit
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@objc public class TextFieldHelper: NSObject {
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// Used to implement the UITextFieldDelegate method: `textField:shouldChangeCharactersInRange:replacementString`
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// Takes advantage of Swift's superior unicode handling to append partial pasted text without splitting multi-byte characters.
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@objc public class func textField(_ textField: UITextField, shouldChangeCharactersInRange editingRange: NSRange, replacementString: String, byteLimit: UInt) -> Bool {
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let byteLength = { (string: String) -> UInt in
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return UInt(string.utf8.count)
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}
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let existingString = textField.text ?? ""
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// Given an NSRange, we need to interact with the NS flavor of substring
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let removedString = (existingString as NSString).substring(with: editingRange)
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let lengthOfRemainingExistingString = byteLength(existingString) - byteLength(removedString)
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let newLength = lengthOfRemainingExistingString + byteLength(replacementString)
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if (newLength <= byteLimit) {
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return true
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}
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// Don't allow any change if inserting a single char is already over the limit (typically this means typing)
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if (replacementString.count < 2) {
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return false
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}
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// However if pasting, accept as much of the string as possible.
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let availableSpace = byteLimit - lengthOfRemainingExistingString
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var acceptableSubstring = ""
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for (_, char) in replacementString.enumerated() {
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var maybeAcceptableSubstring = acceptableSubstring
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maybeAcceptableSubstring.append(char)
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if (byteLength(maybeAcceptableSubstring) <= availableSpace) {
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acceptableSubstring = maybeAcceptableSubstring
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} else {
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break
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}
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}
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textField.text = (existingString as NSString).replacingCharacters(in: editingRange, with: acceptableSubstring)
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// We've already handled any valid editing manually, so prevent further changes.
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return false
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}
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}
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