如何在 Xamarin 中使用 UITextView 实现 iOS 的隐藏/显示密码样式体验？

Question

我知道UITextFields可以使用SecureTextEntry属性实现密码风格的效果，我也在网上找到了一些代码来实现隐藏/显示密码效果here，但这仅适用于@987654326 @，我需要为自定义 UITextView 实现相同的功能。我目前有一些代码来实现为UI添加图像，但没有实现实际的显示/隐藏密码效果。

我在Swifthere 中找到了一些关于如何执行此操作的代码，但我从未与Swift 合作过，希望熟悉Swift 的人可以为我将其翻译成C# ，因为这可能是我需要的解决方案。

我也明白，虽然SecureTextEntry 属性在设置为 true 时为UITextFields 提供密码风格的体验（即防止复制并将字符变成黑点），它仅在为 UITextViews 设置为 true 时防止复制文本。这是我从这个属性的文档中找到的 here

这是我目前在文件中实现显示/隐藏密码效果的代码：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using UIKit;
using Xamarin.Forms;
using Xamarin.Forms.Platform.iOS;

[assembly: ResolutionGroupName("Xamarin")]
[assembly:ExportEffect(typeof(MyApp.iOS.CustomRenderers.PasswordEffect), "PasswordEffect")]
namespace MyApp.iOS.CustomRenderers
{
    public class PasswordEffect : PlatformEffect
    {
        protected override void OnAttached()
        {
            Configure();
        }

        protected override void OnDetached()
        {
            //do nothing
        }

        private void Configure()
        {
            if (Control != null)
            {
                if (Control is UITextView) {
                    UITextView vUpdatedEntry = (UITextView)Control;
                    var buttonRect = UIButton.FromType(UIButtonType.Custom);
                    buttonRect.SetImage(UIImage.FromBundle("eye_image"), UIControlState.Normal);
                    buttonRect.TouchUpInside += (object sender, EventArgs e1) => {
                        if (vUpdatedEntry.SecureTextEntry)
                        {
                            vUpdatedEntry.SecureTextEntry = false;
                            buttonRect.SetImage(UIImage.FromBundle("eye_crossed_image"), UIControlState.Normal);
                        }
                        else
                        {
                            vUpdatedEntry.SecureTextEntry = true;
                            buttonRect.SetImage(UIImage.FromBundle("eye_image"), UIControlState.Normal);
                        }
                    };
                    // Would love to have password effect here :)
                    vUpdatedEntry.ShouldChangeText += (textField, range, replacementString) => {
                        string text = vUpdatedEntry.Text;
                        var result = text.Substring(0, (int)range.Location) + replacementString + text.Substring((int)range.Location + (int)range.Length);
                        vUpdatedEntry.Text = result;
                        return false;
                    };

                    buttonRect.Frame = new CoreGraphics.CGRect(10.0f, 0.0f, 15.0f, 15.0f);
                    buttonRect.ContentMode = UIViewContentMode.ScaleToFill;

                    UIView paddingViewRight = new UIView(new System.Drawing.RectangleF(0.0f, 0.0f, 30.0f, 18.0f));
                    paddingViewRight.AddSubview(buttonRect);

                    buttonRect.TranslatesAutoresizingMaskIntoConstraints = false;
                    buttonRect.CenterYAnchor.ConstraintEqualTo(paddingViewRight.CenterYAnchor).Active = true;

                    vUpdatedEntry.TextContainerInset = new UIEdgeInsets(8.0f, 0.0f, 8.0f, paddingViewRight.Frame.Width+5.0f);
                    vUpdatedEntry.AddSubview(paddingViewRight);

                    paddingViewRight.TranslatesAutoresizingMaskIntoConstraints = false;
                    paddingViewRight.TrailingAnchor.ConstraintEqualTo(vUpdatedEntry.LayoutMarginsGuide.TrailingAnchor, 9.0f).Active = true;
                    paddingViewRight.HeightAnchor.ConstraintEqualTo(vUpdatedEntry.HeightAnchor).Active = true;
                    paddingViewRight.WidthAnchor.ConstraintEqualTo(buttonRect.WidthAnchor,1.0f, 0.0f).Active = true;

                    Control.Layer.CornerRadius = 4;
                    Control.Layer.BorderColor = new CoreGraphics.CGColor(255, 255, 255);
                    Control.Layer.MasksToBounds = true;
                    vUpdatedEntry.TextAlignment = UITextAlignment.Left;
                }
            }
        }

    }
}

Answer 1

你可以定义一个自定义的UITextViewDelegate来实现它。

public class TextViewDelegate : UITextViewDelegate
{
    private UITextView myTextView;
    bool secureTextViewEntry;       // default is NO
    NSMutableString secureText;
    NSTimer timer;
    NSString lastText;
    public TextViewDelegate(UITextView myTextView)
    {
        this.myTextView = myTextView; 
        secureTextViewEntry = false;
        secureText = new NSMutableString();
    }

    public override bool ShouldChangeText(UITextView textView, NSRange range, string text)
    {
        if("\n" == text)
        {
            textView.ResignFirstResponder();
            return false;
        }
        lastText = new NSString(text);
        return true;
        //return base.ShouldChangeText(textView, range, text);
    }

    public override void Changed(UITextView textView)
    {
        Console.WriteLine("-----" + secureText);
        if (secureTextViewEntry)
        {
            string text = textView.Text;
            if(text.Length > 0)
            {
                if("" == lastText)
                {
                    secureText.DeleteCharacters(new NSRange(secureText.Length - 1, 1));
                    onlyPassword();
                    if (null != timer)
                    {
                        timer.Invalidate();
                    }
                    //base.Changed(textView);
                    return;
                }
                else
                {
                    NSString one = new NSString(text.Substring(text.Length - 1));
                    secureText.Append(one);
                    NSMutableString temp = new NSMutableString();
                    for (int i = 0; i < secureText.Length - 1; i++)
                    {
                        temp.Append(new NSString("•"));
                    }
                    temp.Append(new NSString(secureText.ToString().Substring(secureText.ToString().Length - 1)));
                    myTextView.Text = temp;

                    if (null != timer)
                    {
                        timer.Invalidate();
                    }
                    timer =NSTimer.CreateScheduledTimer(2, onlyPassword);
                }
            }
            else
            {
                secureText = new NSMutableString();

            }
            //base.Changed(textView);
        }
        else {
            if (textView.Text.Length == 0)
            {
                secureText = new NSMutableString();
            }
            else
            {
                secureText = new NSMutableString();
                secureText.SetString(new NSString(textView.Text));
            }
            if(null != timer) {
                timer.Invalidate();
            }

            //base.Changed(textView);
        }
    }


    private void onlyPassword(NSTimer obj)
    {
        //throw new NotImplementedException();
        onlyPassword();
    }

    private void onlyPassword()
    {
        //throw new NotImplementedException();
        timer.Invalidate();
        NSMutableString temp = new NSMutableString();
        for(int i = 0; i< secureText.Length; i++)
        {
            temp.Append(new NSString("•"));
        }
        myTextView.Text = temp;
    }

    public override void DidChange(NSKeyValueChange changeKind, NSIndexSet indexes, NSString forKey)
    {
        base.DidChange(changeKind, indexes, forKey);
    }
    //set Secure be true or false
    public void setSecureTextViewEntry(bool _secureTextViewEntry)
    {
        secureTextViewEntry = _secureTextViewEntry;
        if (secureText.Length == 0)
        {
            return;
        }
        else
        {
            if (secureTextViewEntry)
            {
                //secret
                NSMutableString aaa = new NSMutableString();
                for (int i = 0; i < secureText.Length; i++)
                {
                    aaa.Append(new NSString("•"));
                }
                myTextView.Text = aaa;
            }else{
                //real word
                myTextView.Text = secureText;
                if (null != timer)
                {
                    timer.Invalidate();
                }
            }
        }
        Changed(myTextView);
    }

    public bool getSecureTextViewEntry()
    {
        return secureTextViewEntry;
    }
}

在 ViewController 中：

TextViewDelegate textViewDelegate;

public override void ViewDidLoad ()
{
     base.ViewDidLoad ();

     textViewDelegate = new TextViewDelegate(MyTextView);
     MyTextView.Delegate = textViewDelegate; //MyTextView from StoryBoard

}

partial void SetTrueButton_TouchUpInside(UIButton sender)
{
    textViewDelegate.setSecureTextViewEntry(true);
}

partial void SetFalseButton_TouchUpInside(UIButton sender)
{
    textViewDelegate.setSecureTextViewEntry(false);
}

效果如下：

注意：代码仅供参考，代码中有一些小问题需要改进。

Answer 2

经过一番努力，我终于能够完成这项工作。非常感谢@JuniorJiang-MSFT 引导我朝着正确的方向前进。我的实现效果的文件的代码如下所示：

using System;
using UIKit;
using Xamarin.Forms;
using Xamarin.Forms.Platform.iOS;
using Foundation;

[assembly: ResolutionGroupName("Xamarin")]
[assembly: ExportEffect(typeof(MyApp.iOS.CustomRenderers.ShowHidePasswordEffect), "ShowHidePasswordEffect")]
namespace MyApp.iOS.CustomRenderers
{
    public class ShowHidePasswordEffect : PlatformEffect
    {
        //The actual text entered by the user.
        private NSMutableString SecureText;
        private NSTimer timer;
        //The last character(s) entered by the user.
        private NSString LastText;
        private UITextView UiTextViewForControl;
        protected override void OnAttached()
        {
            SecureText = new NSMutableString();
            ConfigureControl();
        }

        protected override void OnDetached()
        {
            //do nothing
        }


        private void ConfigureControl()
        {
            if (Control != null)
            { 
                if (Control is UITextView) {
                    UITextView vUpdatedEntry = (UITextView)Control;
                    this.UiTextViewForControl = vUpdatedEntry;

                    var buttonRect = UIButton.FromType(UIButtonType.Custom);
                    buttonRect.SetImage(UIImage.FromBundle("show_black_24"), UIControlState.Normal);
                    buttonRect.TouchUpInside += (object sender, EventArgs e1) => {
                        if (vUpdatedEntry.SecureTextEntry)
                        {
                            vUpdatedEntry.SecureTextEntry = false;
                            buttonRect.SetImage(UIImage.FromBundle("hide_black_24"), UIControlState.Normal);
                        }
                        else
                        {
                            vUpdatedEntry.SecureTextEntry = true;
                            buttonRect.SetImage(UIImage.FromBundle("show_black_24"), UIControlState.Normal);
                        }
                        // Change the text based on whether password is to be hidden or visible.
                        HandleSecureEntryChange(vUpdatedEntry);
                    };

                    vUpdatedEntry.ShouldChangeText += (textView, range, toReplaceText) => {
                        if ("\n" == toReplaceText)
                        {   //Drop the keyboard if 'Enter/Return' is pressed
                            vUpdatedEntry.ResignFirstResponder();
                            return false;
                        }
                        //Get the text that was entered, store that in LastText. Return true, so that Changed is called.
                        LastText = new NSString(toReplaceText);
                        return true;
                    };
                    // Add eventHandler for Changed.
                    vUpdatedEntry.Changed += HandleTextChange;

                    buttonRect.ContentMode = UIViewContentMode.ScaleToFill;

                    UIView paddingViewRight = new UIView(new System.Drawing.RectangleF(0.0f, 0.0f, 30.0f, 18.0f));
                    paddingViewRight.AddSubview(buttonRect);

                    buttonRect.TranslatesAutoresizingMaskIntoConstraints = false;
                    buttonRect.CenterYAnchor.ConstraintEqualTo(paddingViewRight.CenterYAnchor).Active = true;

                    vUpdatedEntry.AddSubview(paddingViewRight);

                    paddingViewRight.TranslatesAutoresizingMaskIntoConstraints = false;
                    paddingViewRight.TrailingAnchor.ConstraintEqualTo(vUpdatedEntry.LayoutMarginsGuide.TrailingAnchor, 8.0f).Active = true;
                    paddingViewRight.HeightAnchor.ConstraintEqualTo(vUpdatedEntry.HeightAnchor).Active = true;
                    paddingViewRight.BottomAnchor.ConstraintEqualTo(vUpdatedEntry.LayoutMarginsGuide.BottomAnchor).Active = true;
                    paddingViewRight.TopAnchor.ConstraintEqualTo(vUpdatedEntry.LayoutMarginsGuide.TopAnchor, -8.0f).Active = true;
                    paddingViewRight.WidthAnchor.ConstraintEqualTo(buttonRect.WidthAnchor, 1.0f, 3.0f).Active = true;
                    vUpdatedEntry.TextContainerInset = new UIEdgeInsets(8.0f, 0.0f, 8.0f, paddingViewRight.Frame.Width + 5.0f);

                    Control.Layer.CornerRadius = 4;
                    Control.Layer.BorderColor = new CoreGraphics.CGColor(255, 255, 255);
                    Control.Layer.MasksToBounds = true;
                    vUpdatedEntry.TextAlignment = UITextAlignment.Left;
                }
            }
        }

        private void HandleTextChange(object sender, EventArgs e)
        {
            UITextView customEditor = (UITextView)sender;
            if (customEditor.SecureTextEntry)
            {
                string text = customEditor.Text;
                if (text.Length > 0)
                {
                    //If LastText is empty, that means deletion occured.
                    if ("" == this.LastText)
                    {   //Delete the last character from the actual text
                        this.SecureText.DeleteCharacters(new NSRange(this.SecureText.Length - 1, 1));
                        if (null != timer)
                        {
                            timer.Invalidate();
                        }
                        return;
                    }
                    // If LastText is not empty, that means (a) new character(s) was/were entered.
                    int lastTextLength = ((this.LastText.ToString()).Length); //Number of characters in LastText.
                    if (lastTextLength > 1)
                    {   // If more than one character was entered (usually by pasting)
                        int NewTextStartIndex = (text.Length - lastTextLength);
                        string TempNewCharacters = text.Substring(NewTextStartIndex);
                        // Get all the characters except the last character and add them to the secureText
                        NSString NewCharacters = new NSString(TempNewCharacters.Substring(0, TempNewCharacters.Length - 1));
                        SecureText.Append(NewCharacters);

                    }
                    // Get and add the last character
                    NSString LastCharacter = new NSString(text.Substring(text.Length - 1));
                    this.SecureText.Append(LastCharacter);
                    // Change all characters to '●' except the last character
                    NSMutableString temp = new NSMutableString();
                    for (int i = 0; i < this.SecureText.Length - 1; i++)
                    {
                        temp.Append(new NSString("●"));

                    }
                    // Add the last character as a plain text to the temp and set that into the editor.
                    temp.Append(new NSString(this.SecureText.ToString().Substring(this.SecureText.ToString().Length - 1)));
                    customEditor.Text = temp;

                    if (null != this.timer)
                    {
                        this.timer.Invalidate();
                    }
                    // Wait two seconds before changing the last character to '●'.
                    this.timer = NSTimer.CreateScheduledTimer(2, ChangeToHidden);
                }
                else
                {
                    this.SecureText = new NSMutableString();
                }
            }
            else
            {
                // If the password is plain text, then initialize it to the secureText string.
                SecureText = new NSMutableString();
                SecureText.SetString(new NSString(customEditor.Text));
                if (null != timer)
                {
                    this.timer.Invalidate();
                }
            }
            CustomEditor ActualCustomEditor = (CustomEditor)Element;
            ActualCustomEditor.PlainText = SecureText.ToString();
        }

        private void ChangeToHidden(object sender)
        {
            // Change all the text entered to '●'
            UITextView customEditor = this.UiTextViewForControl;
            this.timer.Invalidate();
            NSMutableString temp = MakeHiddenText();
            customEditor.Text = temp;
        }

        private void HandleSecureEntryChange(object sender)
        {
            if (this.SecureText.Length > 0)
            {   // If SecureTextEntry is true, hide text, else make plain text and clean the timer.
                UITextView customEditor = (UITextView)sender;
                if (customEditor.SecureTextEntry)
                {
                    NSMutableString temp = MakeHiddenText();
                    customEditor.Text = temp;
                }
                else
                {
                    customEditor.Text = this.SecureText;
                    if (null != timer)
                    {
                        this.timer.Invalidate();
                    }
                }
            }
        }

        private NSMutableString MakeHiddenText()
        //Make string of '●''s for the text and return
        {
            NSMutableString temp = new NSMutableString();
            for (int i = 0; i < this.SecureText.Length; i++)
            {
                temp.Append(new NSString("●"));
            }
            return temp;
        }

    }
}

我的 CustomRenderer 的代码如下所示：

using MyApp.CustomControls;
using MyApp.iOS.CustomRenderers;
using UIKit;
using Xamarin.Forms;
using Xamarin.Forms.Platform.iOS;

[assembly: ExportRenderer(typeof(CustomEditor), typeof(CustomEditorRenderer))]
namespace MyApp.iOS.CustomRenderers
{
    public class CustomEditorRenderer: EditorRenderer
    {
        protected override void OnElementChanged(ElementChangedEventArgs<Editor> e)
        {
            base.OnElementChanged(e);
            if (Control != null && Element != null) {
                var element = (CustomEditor)this.Element;
                if (element.IsPassword) {
                    UITextView uiTextView = (UITextView)Control;
                    uiTextView.SecureTextEntry = true;
                }
            }
        }
    }
}

在子类Editor 的文件中，我添加了一个属性PlainText，它将用于在隐藏时获取实际文本。在我的 XAML 中，我将此属性绑定到应该保存输入到控件中的文本的变量。下面是我CustomEditor的相关代码。

using System;
using System.Collections.Generic;
using System.Text;
using Xamarin.Forms;

namespace MyApp.CustomControls
{
    public class CustomEditor : Editor
    {
        public static readonly BindableProperty PlainTextProperty =
            BindableProperty.Create(nameof(PlainText),
                typeof(string),
                typeof(CustomEditor),
                String.Empty,
                defaultBindingMode:BindingMode.TwoWay,
                propertyChanged:OnPlainTextChanged);

        public string PlainText {
            get { return (string)GetValue(PlainTextProperty); }
            set { SetValue(PlainTextProperty, value); }
        }

        private static void OnPlainTextChanged(BindableObject bindable, object oldValue, object newValue)
        {
            var control = (CustomEditor)bindable;
            if (newValue != null)
            {
                control.PlainText = newValue.ToString();
            }
        }
    }
}

注意：必须将defaultBindingMode 指定为TwoWay，并为propertyChanged 指定一个方法才能使其工作。

Answer 3

您的问题分为两部分。

1. 您可能可以通过子类化 UITextView 来防止复制和粘贴内容，如下所示：

public class ProtectedTextView : UITextView
{
    public override bool CanPerform(Selector action, NSObject withSender)
    {
        if (action == new Selector("paste:") || (action == new Selector("copy:")))
            return false;
        else
            return base.CanPerform(action, withSender);
    }
}

1. 对于显示/隐藏，您正在查看的内容相当于：

textView.ShouldChangeText = (textField, range, replacementString) =>
{
     string text = textView.Text;
     var result = text.Substring(0, (int) range.Location) + replacementString + text.Substring((int) range.Location + (int) range.Length);
     textView.Text = result;
     return false;
};

我还没有测试代码是否可以工作，所以如果您有任何问题，请告诉我。