StringLengthAttribute.cs

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using System.Globalization;
 
namespace System.ComponentModel.DataAnnotations;
 
[AttributeUsage(AttributeTargets.Property | AttributeTargets.Field | AttributeTargets.Parameter, AllowMultiple = false)]
public class StringLengthAttribute : ValidationAttribute
{
    public int MaximumLength { get; }
 
    public int MinimumLength { get; set; }
 
    public StringLengthAttribute(int maximumLength)
        : base(() => System.SR.StringLengthAttribute_ValidationError)
    {
        MaximumLength = maximumLength;
    }
 
    public override bool IsValid(object? value)
    {
        EnsureLegalLengths();
        if (value == null)
        {
            return true;
        }
        int length = ((string)value).Length;
        if (length >= MinimumLength)
        {
            return length <= MaximumLength;
        }
        return false;
    }
 
    public override string FormatErrorMessage(string name)
    {
        EnsureLegalLengths();
        string format = ((MinimumLength != 0 && !base.CustomErrorMessageSet) ? System.SR.StringLengthAttribute_ValidationErrorIncludingMinimum : base.ErrorMessageString);
        return string.Format(CultureInfo.CurrentCulture, format, name, MaximumLength, MinimumLength);
    }
 
    private void EnsureLegalLengths()
    {
        if (MaximumLength < 0)
        {
            throw new InvalidOperationException(System.SR.StringLengthAttribute_InvalidMaxLength);
        }
        if (MaximumLength < MinimumLength)
        {
            throw new InvalidOperationException(System.SR.Format(System.SR.RangeAttribute_MinGreaterThanMax, MaximumLength, MinimumLength));
        }
    }
}