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C# code
using System.Collections.Generic;
using System.Windows;

namespace WPFDataBinding
    public partial class MainWindow : Window
        public Person Obj { get; set; }

        public MainWindow()
            Obj = new Person();

            List<string> subjects1 = new List<string>();

            List<string> subjects2 = new List<string>();

            Obj.studDetail.Add("Kush", subjects1);
            Obj.studDetail.Add("Yash", subjects2);

            DataContext = this;

        public class Person
            private Dictionary<string, List<string>> StudDetail;

            public Dictionary<string, List<string>> studDetail
                get { return StudDetail; }
                    if (StudDetail != null)
                        StudDetail = value;


<Window x:Class="WPFDataBinding.MainWindow"
        Title="MainWindow" Height="350" Width="525">
    <StackPanel Background="Gray">

What I have tried:

i googled but didn't find anything which helps. Please help
Updated 16-Jul-18 23:18pm
#realJSOP 17-Jul-18 4:04am     CRLF
WHERE is the exception being thrown? It looks like all of your xaml isn't there...
F-ES Sitecore 17-Jul-18 4:22am    
I just googled "object reference not set to an instance of an object" and got 27,000,000 results. Maybe at least go through the first 10.

You are not initialising the object StudDetail in your Person class so this line will fail
Obj.studDetail.Add("Kush", subjects1);
Somewhere in that class (e.g. in a class constructor or in the get/set code for the property) you need
studDetail = new Dictionary<string, List<string>>();
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This is one of the most common problems we get asked, and it's also the one we are least equipped to answer, but you are most equipped to answer yourself.

Let me just explain what the error means: You have tried to use a variable, property, or a method return value but it contains null - which means that there is no instance of a class in the variable.
It's a bit like a pocket: you have a pocket in your shirt, which you use to hold a pen. If you reach into the pocket and find there isn't a pen there, you can't sign your name on a piece of paper - and you will get very funny looks if you try! The empty pocket is giving you a null value (no pen here!) so you can't do anything that you would normally do once you retrieved your pen. Why is it empty? That's the question - it may be that you forgot to pick up your pen when you left the house this morning, or possibly you left the pen in the pocket of yesterdays shirt when you took it off last night.

We can't tell, because we weren't there, and even more importantly, we can't even see your shirt, much less what is in the pocket!

Back to computers, and you have done the same thing, somehow - and we can't see your code, much less run it and find out what contains null when it shouldn't.
But you can - and Visual Studio will help you here. Run your program in the debugger and when it fails, VS will show you the line it found the problem on. You can then start looking at the various parts of it to see what value is null and start looking back through your code to find out why. So put a breakpoint at the beginning of the method containing the error line, and run your program from the start again. This time, VS will stop before the error, and let you examine what is going on by stepping through the code looking at your values.

But we can't do that - we don't have your code, we don't know how to use it if we did have it, we don't have your data. So try it - and see how much information you can find out!
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