RequiredAttribute.cs

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namespace System.ComponentModel.DataAnnotations;
 
[AttributeUsage(AttributeTargets.Property | AttributeTargets.Field | AttributeTargets.Parameter, AllowMultiple = false)]
public class RequiredAttribute : ValidationAttribute
{
    public bool AllowEmptyStrings { get; set; }
 
    public RequiredAttribute()
        : base(() => System.SR.RequiredAttribute_ValidationError)
    {
    }
 
    public override bool IsValid(object? value)
    {
        if (value == null)
        {
            return false;
        }
        if (!AllowEmptyStrings && value is string value2)
        {
            return !string.IsNullOrWhiteSpace(value2);
        }
        return true;
    }
}