Using base View Model Class with GalaSoft MVVM Light

Question

I am creating a project using WPF and MVVM-Light library from GalaSoft. I will have a base abstract View Model class, which will be used by all other View Model classes implemented. There I will have MVVM-Light base class as my base class. However, inside this base class, when I try to use RaisePropertyChanged function I get the following error:

An object reference is required for the non-static field, method, or property 'GalaSoft.MvvmLight.ViewModelBase.RaisePropertyChanged(string)'

The code will look like this:

AnalysisViewModelBase : ViewModelBase
{
    public const string TagDescriptionStringListPropertyName = "TagDescriptionStringList";

    protected static List<string> m_tagDescriptionStringList;

    public static List<string> TagDescriptionStringList 
    { 
        get 
        { return m_tagDescriptionStringList; }
        set
        {
            if (m_tagDescriptionStringList == value)
                return;

            m_tagDescriptionStringList = value;

            RaisePropertyChanged(TagDescriptionStringListPropertyName);
        }

    }
    protected AnalysisViewModelBase()
    {
        m_tagDescriptionStringList = new List<string>();

        m_tagDescriptionStringList.AddRange(new string[] { "North Position", "East Position", "Depth" });
    }
}

AnotherViewModel : AnalysisViewModelBase
{ ... }

Could anyone please help me understand what is wrong with my RaiseProperyChanged function?

Answer 1

You are trying to access a Non Static Method From a Static Method... It does not have access to this value, you have to make your method non static.

here is a web page which explains about static methods if you want to have a better understanding of why you can't do what you are trying to do.

Link

Answer 2

You simply must declare your property "Tax DescriptionStringList " as non static. Since the backingfield (m_tagDescriptionStringList) is static it remains the same thing. Make this :

class AnalysisViewModelBase : ViewModelBase
{
    public const string TagDescriptionStringListPropertyName = "TagDescriptionStringList";

    protected static List<string> m_tagDescriptionStringList;

    public List<string> TagDescriptionStringList 
    { 
        get 
        { return m_tagDescriptionStringList; }
        set
        {
            if (m_tagDescriptionStringList == value)
                return;

            m_tagDescriptionStringList = value;

            RaisePropertyChanged(TagDescriptionStringListPropertyName);
        }
    }

    protected AnalysisViewModelBase()
    {
        m_tagDescriptionStringList = new List<string>();

        m_tagDescriptionStringList.AddRange(new string[] { "North Position", "East Position", "Depth" });
    }
}

AnotherViewModel : AnalysisViewModelBase
{ ... }

If it is absolutely necessary to keep the property as a static property in this case, here is a solution: raise the property changes (using RaisePropertyChanged("TagDescriptionStringList")) when it happens, as I indicated in the code below

class AnalysisViewModelBase : ViewModelBase
    {
        public const string TagDescriptionStringListPropertyName = "TagDescriptionStringList";

        protected static List<string> m_tagDescriptionStringList;

        public static List<string> TagDescriptionStringList 
        { 
            get 
            { return m_tagDescriptionStringList; }
            set
            {
                if (m_tagDescriptionStringList != value) 
                {  
                    m_tagDescriptionStringList = value;
                }
            }
        }

        protected AnalysisViewModelBase()
        {
            m_tagDescriptionStringList = new List<string>();

            m_tagDescriptionStringList.AddRange(new string[] { "North Position", "East Position", "Depth" });

            RaisePropertyChanged("TagDescriptionStringList");

        }
    }

    AnotherViewModel : AnalysisViewModelBase
    { ... }