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TextBox Editing, Clipboard, Undo/Redo, and Text Input Options

Table of Contents

1. Scope and APIs
2. Baseline TextBox Authoring
3. Selection and Caret Control
4. Clipboard Pipeline (Cut, Copy, Paste)
5. Undo/Redo and Edit History
6. Text Input Options for Virtual Keyboard/IME
7. Programmatic Patterns in C#
8. Best Practices
9. Troubleshooting

Scope and APIs

Primary APIs:

• TextBox
• TextInputOptions
• TextInputContentType
• TextInputReturnKeyType
• InputElement.TextInputMethodClientRequestedEvent

Important TextBox members:

• Text, CaretIndex, SelectionStart, SelectionEnd, SelectedText
• AcceptsReturn, AcceptsTab, TextWrapping
• IsReadOnly, PasswordChar, RevealPassword
• MaxLength, MaxLines, MinLines
• PlaceholderText, PlaceholderForeground, UseFloatingPlaceholder
• CanCut, CanCopy, CanPaste, CanUndo, CanRedo
• IsUndoEnabled, UndoLimit
• ClearSelection(), SelectAll(), Clear(), ScrollToLine(int)
• Cut(), Copy(), Paste(), Undo(), Redo()
• CopyingToClipboard, CuttingToClipboard, PastingFromClipboard
• TextChanging, TextChanged
• static gestures: CutGesture, CopyGesture, PasteGesture

Important TextInputOptions attached properties:

• TextInputOptions.ContentType
• TextInputOptions.ReturnKeyType
• TextInputOptions.Multiline
• TextInputOptions.AutoCapitalization
• TextInputOptions.IsSensitive
• TextInputOptions.Lowercase
• TextInputOptions.Uppercase
• TextInputOptions.ShowSuggestions

Reference source files:

• src/Avalonia.Controls/TextBox.cs
• src/Avalonia.Base/Input/TextInput/TextInputOptions.cs
• src/Avalonia.Base/Input/TextInput/TextInputContentType.cs
• src/Avalonia.Base/Input/TextInput/TextInputReturnKeyType.cs

Baseline TextBox Authoring

<TextBox xmlns="https://github.com/avaloniaui"
         xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
         Width="360"
         Text="{Binding Notes}"
         AcceptsReturn="True"
         TextWrapping="Wrap"
         MaxLines="6"
         PlaceholderText="Write a note..." />

Single-line defaults are usually enough for search/filter boxes. Use AcceptsReturn + TextWrapping for document-like input.

Selection and Caret Control

CaretIndex, SelectionStart, and SelectionEnd are style/binding-friendly properties.

using Avalonia.Controls;

void HighlightAll(TextBox textBox)
{
    textBox.SelectAll();
}

void MoveCaretToEnd(TextBox textBox)
{
    var textLength = textBox.Text?.Length ?? 0;
    textBox.CaretIndex = textLength;
    textBox.SelectionStart = textLength;
    textBox.SelectionEnd = textLength;
}

Use ClearSelection() to collapse selection while preserving caret location semantics.

Clipboard Pipeline (Cut, Copy, Paste)

TextBox exposes routed clipboard events and imperative methods.

using Avalonia.Controls;
using Avalonia.Interactivity;

void WireClipboardGuards(TextBox textBox)
{
    textBox.CopyingToClipboard += OnCopying;
    textBox.CuttingToClipboard += OnCutting;
    textBox.PastingFromClipboard += OnPasting;
}

void OnCopying(object? sender, RoutedEventArgs e)
{
    // e.Handled = true; // enable if copy should be blocked.
}

void OnCutting(object? sender, RoutedEventArgs e)
{
}

void OnPasting(object? sender, RoutedEventArgs e)
{
}

Shortcut notes:

• CutGesture, CopyGesture, PasteGesture expose platform-preferred defaults.
• If you provide custom KeyBindings, keep behavior consistent with these defaults.

Undo/Redo and Edit History

Use the built-in history rather than custom stacks where possible.

<TextBox xmlns="https://github.com/avaloniaui"
         xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
         Text="{Binding Script}"
         IsUndoEnabled="True"
         UndoLimit="200" />

void ApplyUndoRedo(TextBox textBox)
{
    if (textBox.CanUndo)
        textBox.Undo();

    if (textBox.CanRedo)
        textBox.Redo();
}

Text Input Options for Virtual Keyboard/IME

TextInputOptions configures keyboard and IME behavior via attached properties.

<TextBox xmlns="https://github.com/avaloniaui"
         xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
         Width="320"
         TextInputOptions.ContentType="Email"
         TextInputOptions.ReturnKeyType="Done"
         TextInputOptions.Multiline="False"
         TextInputOptions.AutoCapitalization="False"
         TextInputOptions.ShowSuggestions="True"
         PlaceholderText="name@example.com" />

Sensitive input pattern:

<TextBox xmlns="https://github.com/avaloniaui"
         xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
         PasswordChar="*"
         TextInputOptions.ContentType="Password"
         TextInputOptions.IsSensitive="True"
         TextInputOptions.ShowSuggestions="False" />

At runtime, effective options can be read with TextInputOptions.FromStyledElement(...).

Programmatic Patterns in C#

using Avalonia.Controls;
using Avalonia.Input.TextInput;

void ConfigureInput(TextBox textBox)
{
    TextInputOptions.SetContentType(textBox, TextInputContentType.Search);
    TextInputOptions.SetReturnKeyType(textBox, TextInputReturnKeyType.Search);
    TextInputOptions.SetShowSuggestions(textBox, true);
}

void MoveToLine(TextBox textBox, int line)
{
    textBox.ScrollToLine(line);
}

Best Practices

• Prefer binding on Text with validation enabled (default for TextProperty).
• Keep clipboard handlers lightweight; avoid blocking UI thread.
• Use CanCut/CanCopy/CanPaste and CanUndo/CanRedo to drive command availability.
• Set TextInputOptions explicitly for mobile and tablet scenarios.
• Use PlaceholderText; keep Watermark aliases only for legacy compatibility.

Troubleshooting

1. Undo/redo never activates.
   • Check IsUndoEnabled and avoid replacing Text on every keystroke from external code.
2. Paste command disabled unexpectedly.
   • Verify IsReadOnly, selection state, and clipboard availability (CanPaste).
3. Virtual keyboard type does not match intent.
   • Confirm TextInputOptions.ContentType and ReturnKeyType are set on the focused control.
4. Text wrapping not applied.
   • Ensure AcceptsReturn="True" for multiline editing and set TextWrapping explicitly.
5. Clipboard event not firing.
   • Subscribe to CopyingToClipboard, CuttingToClipboard, and PastingFromClipboard on the actual active TextBox instance.

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