Validate Input Attribute

[HideLabel]
[Title("Default message", "You can just provide a default message that is always used")]
[ValidateInput("MustBeNull", "This field should be null.")]
public MyScriptyScriptableObject DefaultMessage;

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[Title("Dynamic message", "Or the validation method can dynamically provide a custom message")]
[ValidateInput("HasMeshRendererDynamicMessage", "Prefab must have a MeshRenderer component")]
public GameObject DynamicMessage;

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[Title("Dynamic message type", "The validation method can also control the type of the message")]
[ValidateInput("HasMeshRendererDynamicMessageAndType", "Prefab must have a MeshRenderer component")]
public GameObject DynamicMessageAndType;

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[InfoBox("Change GameObject value to update message type", InfoMessageType.None)]
public InfoMessageType MessageType;

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[Title("Dynamic default message", "Use $ to indicate a member string as default message")]
[ValidateInput("AlwaysFalse", "$Message", InfoMessageType.Warning)]
public string Message = "Dynamic ValidateInput message";

private bool AlwaysFalse(string value)
{
    return false;
}

private bool MustBeNull(MyScriptyScriptableObject scripty)
{
    return scripty == null;
}

private bool HasMeshRendererDefaultMessage(GameObject gameObject)
{
    if (gameObject == null) return true;

    return gameObject.GetComponentInChildren<MeshRenderer>() != null;
}

private bool HasMeshRendererDynamicMessage(GameObject gameObject, ref string errorMessage)
{
    if (gameObject == null) return true;

    if (gameObject.GetComponentInChildren<MeshRenderer>() == null)
    {
        // If errorMessage is left as null, the default error message from the attribute will be used
        errorMessage = "\"" + gameObject.name + "\" must have a MeshRenderer component";

        return false;
    }

    return true;
}

private bool HasMeshRendererDynamicMessageAndType(GameObject gameObject, ref string errorMessage, ref InfoMessageType? messageType)
{
    if (gameObject == null) return true;

    if (gameObject.GetComponentInChildren<MeshRenderer>() == null)
    {
        // If errorMessage is left as null, the default error message from the attribute will be used
        errorMessage = "\"" + gameObject.name + "\" should have a MeshRenderer component";

        // If messageType is left as null, the default message type from the attribute will be used
        messageType = this.MessageType;

        return false;
    }

    return true;
}