如何通过KeyBinding命令实现TextBox内Shift+Return组合键换行

注意：全程不要设置AcceptsReturn="True"，避免单独回车也触发换行

方案1：基于InputBindings命令绑定实现（适配MVVM模式） #

第一步：实现基础命令类 #

项目中添加通用RelayCommand实现，用于绑定KeyBinding的Command属性

public class RelayCommand : ICommand
{
    private readonly Action<object> _execute;
    private readonly Func<object, bool> _canExecute;

    public RelayCommand(Action<object> execute, Func<object, bool> canExecute = null)
    {
        _execute = execute ?? throw new ArgumentNullException(nameof(execute));
        _canExecute = canExecute;
    }

    public bool CanExecute(object parameter) => _canExecute == null || _canExecute(parameter);

    public void Execute(object parameter) => _execute(parameter);

    public event EventHandler CanExecuteChanged
    {
        add => CommandManager.RequerySuggested += value;
        remove => CommandManager.RequerySuggested -= value;
    }
}

第二步：ViewModel中定义换行命令 #

// 声明命令属性
public ICommand InsertNewLineCommand { get; }

// ViewModel构造函数中初始化命令
public YourViewModel()
{
    InsertNewLineCommand = new RelayCommand(obj =>
    {
        if (obj is TextBox textBox)
        {
            int caretIndex = textBox.CaretIndex;
            // 在光标位置插入换行符
            textBox.Text = textBox.Text.Insert(caretIndex, Environment.NewLine);
            // 光标移动到换行符之后，避免跳转至文本末尾
            textBox.CaretIndex = caretIndex + Environment.NewLine.Length;
        }
    });
}

第三步：XAML中配置InputBindings #

<TextBox x:Name="MyTextBox" AcceptsReturn="False">
    <TextBox.InputBindings>
        <KeyBinding Key="Return" Modifiers="Shift" 
                    Command="{Binding InsertNewLineCommand}"
                    CommandParameter="{Binding ElementName=MyTextBox}"/>
    </TextBox.InputBindings>
</TextBox>

如果要简化单独回车触发按钮的逻辑，可直接在窗口根节点配置默认按钮，配置后单独按回车键会自动触发该按钮的点击逻辑，无需额外编码：

<Window DefaultButton="{Binding ElementName=TargetButton}">
    <!-- 其他页面控件 -->
    <Button x:Name="TargetButton" Content="提交" Command="{Binding SubmitCommand}"/>
</Window>

方案2：基于PreviewKeyDown事件实现（快速适配，无需MVVM） #

第一步：XAML中绑定事件 #

<TextBox x:Name="MyTextBox" AcceptsReturn="False" PreviewKeyDown="MyTextBox_PreviewKeyDown"/>

第二步：后台实现事件处理逻辑 #

private void MyTextBox_PreviewKeyDown(object sender, KeyEventArgs e)
{
    if (e.Key == Key.Return)
    {
        if (Keyboard.Modifiers == ModifierKeys.Shift)
        {
            // Shift+回车：插入换行
            var textBox = (TextBox)sender;
            int caret = textBox.CaretIndex;
            textBox.Text = textBox.Text.Insert(caret, Environment.NewLine);
            textBox.CaretIndex = caret + Environment.NewLine.Length;
            e.Handled = true;
        }
        else
        {
            // 单独回车：触发指定按钮逻辑
            // 若按钮绑定命令用以下写法
            TargetButton.Command.Execute(null);
            // 若按钮用Click事件则直接调用逻辑：TargetButton_Click(null, null);
            e.Handled = true;
        }
    }
}

内容的提问来源于stack exchange，提问作者BrindleB