Getting NullReferenceException in Code

What is wrong with this code?

public partial class MainForm : Form
 {
        private Dictionary<String , PropertyInfo[]> types;  
        public MainForm()
        {
            //OpenAccountStruct is in the scope
            types.Add("OpenAccount", new OpenAccountStruct().GetType().GetProperties());
        }
} 

Why am I getting NullR开发者_运维问答eferenceException?

You didn't make an instance of types (your Dictionary).

try

types = new Dictionary<String , PropertyInfo[]>();

The types variable is not initialized. Use types = new Dictionary<String , PropertyInfo[]>();

 private Dictionary<String , PropertyInfo[]> types = 
                        new Dictionary<String , PropertyInfo[]>();

Obviously, your types field is not initialized,

 public partial class MainForm : Form
 {
        private Dictionary<String , PropertyInfo[]> types = new Dictionary<String , PropertyInfo[]>();
        public MainForm()
        {
            //OpenAccountStruct is in the scope
            types.Add("OpenAccount", new OpenAccountStruct().GetType().GetProperties());
        }
}