c# - 在不影响光标位置的情况下将 TextBox 输入限制为特定值

Question

我有一个 WPF 应用程序 (MVVM)。我想限制用户在 TextBox 中输入超过特定值的值。假设该值为 '100' ，那么用户不应该输入 101 等。我尝试了以下代码。

XAML:

<TextBox Text="{Binding SearchText}" FocusManager.FocusedElement="{Binding RelativeSource={RelativeSource Self}}" Name="SearchTextBox"  TextChanged="TextBox_TextChanged"/>

代码:

 private void TextBox_TextChanged(object sender, TextChangedEventArgs e)
    {
        TextBox textBox = sender as TextBox;
        if (textBox != null && !string.IsNullOrEmpty(textBox.Text))
        {
            int searchIndex = 0;
            int count = 100;
            int.TryParse(textBox.Text, out searchIndex);

            if (textBox != null && !string.IsNullOrEmpty(textBox.Text))
            {
                if (searchIndex > Count)
                {
                    textBox.Text = textBox.Text.Substring(0, textBox.Text.Length - 1);
                }
            }
        }
    }

使用此代码，我可以限制用户输入超过特定值的值。但问题是，当我设置 TextBox 的文本时，光标会移动到第一个数字。有解决办法吗？

Answer 1

您可以处理 PreviewTextInput 事件，并在验证时将 TextCompositionEventArgs 的 Handled 属性设置为 true失败:

private void SearchTextBox_PreviewTextInput(object sender, TextCompositionEventArgs e)
{
    TextBox textBox = sender as TextBox;
    if (textBox != null)
    {
        string text = textBox.Text + e.Text;
        if (!string.IsNullOrEmpty(text))
        {
            int searchIndex = 0;
            int count = 100;
            int.TryParse(text, out searchIndex);
            e.Handled = (searchIndex > count);
        }
    }
}

Thanks. You answer has solved my most of the issues. But still if I delete first digit and enter another digit, then the validation fails. Suppose count is 150. I enter 150 & then delete 1 & again enter 1 then textbox will get 501 & validation will fail

好吧，毕竟您应该坚持处理 TextChanged 事件。试试这个:

private void TextBox_TextChanged(object sender, TextChangedEventArgs e)
{
    TextBox textBox = sender as TextBox;
    if (textBox != null)
    {
        const int count = 100;
        int searchIndex = 0;
        int.TryParse(textBox.Text, out searchIndex);
        if (searchIndex > count)
        {
            var textChange = e.Changes.First();
            if (textChange != null && textChange.AddedLength > 0)
            {
                int caret = textBox.CaretIndex;
                int length = textBox.Text.Length;
                textBox.TextChanged -= TextBox_TextChanged;
                textBox.Text = textBox.Text.Substring(0, textChange.Offset) + textBox.Text.Substring(textChange.Offset + textChange.AddedLength);
                textBox.TextChanged += TextBox_TextChanged;
                textBox.CaretIndex = caret - Math.Abs(textBox.Text.Length - length);
            }
        }
    }
}