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    <p>The problem is the following static properties on the <code>ReadFromFile</code> class, if I assume by "overwritten" you mean that both instances of <code>UserFile</code> point to the same data:</p> <pre><code> public static Dictionary&lt;int, Family&gt; families = new Dictionary&lt;int, Family&gt;(); public static Dictionary&lt;int, Individual&gt; individuals = new Dictionary&lt;int, Individual&gt;(); public static Header head; </code></pre> <p>The problem lies in the constructor of <code>UserFile</code> on the use of <strong>static</strong> properties.</p> <pre><code> ReadFromFile.Read(_dir); fileIndividuals = ReadFromFile.individuals; // &lt;-- Uh-oh! fileFamilies = ReadFromFile.families; // &lt;-- Uh-oh! fileHead = ReadFromFile.head; // &lt;-- Uh-oh! </code></pre> <p>What happens here is the member variables <code>fileIndividuals</code>, <code>fileFamilies</code> and <code>fileHead</code> are set to a <strong>reference</strong> of the <code>individuals</code>, <code>families</code> and <code>head</code> properties on the static <code>ReadFromFile</code> class, <strong>not a copy</strong> (as they are classes and not value types). So the next time <code>ReadFromFile.Read()</code> is called the static properties on <code>ReadFromFile</code> are updated (overwritten), but the prior instance of <code>UserFile</code> just points to the <em>same</em> static properties, ergo <code>file1</code> and <code>file2</code> will have the same data.</p> <p>So how would you fix this? Two options:</p> <ol> <li>Make <code>ReadFromFile</code> and instance class, and not a static one. Construct a new instance in the <code>UserFile</code> constructor and don't use <strong>any</strong> static properties.</li> <li>Make a copy of the data in <code>individuals</code>, <code>families</code> and <code>head</code> in the constructor of <code>UserFile</code>. "foreach" through each item, and copy it into a new dictionary. </li> </ol> <hr> <p>Simple explanation: </p> <p>When you do an assign (the = character in C#) if the object is a class, then the target is assigned a "pointer" (reference) to the right hand side. If it's a value type it's copied. Dictionary is a class, so you get a pointer and not a copy. </p> <p>Illustration in code: </p> <pre><code>public static class MyStaticClass { public static List&lt;string&gt; MyList = new List&lt;string&gt; } </code></pre> <p>Elsewhere...</p> <pre><code>public void MyMethod() { List&lt;string&gt; myList1 = MyStaticClass.MyList; List&lt;string&gt; myList2 = MyStaticClass.MyList; myList1.Add("Hello"); // Add to first list myList2.Add("World"); // Add to second list foreach(string item in myList1) // print all items in the second list { Console.WriteLine("List 1: " + item); } foreach(string item in myList2) // print all items in the second list { Console.WriteLine("List 2: " + item); } } </code></pre> <p>The output of this will be: </p> <pre><code>List 1: Hello List 1: World List 2: Hello List 2: World </code></pre> <p>But why? We only added 'World' to <code>myList2</code>. Well <code>myList1</code> and <code>myList2</code> <strong>point</strong> to the same thing. When we did <code>myList1 = MyStaticClass.MyList</code> we didn't get a <strong>copy</strong> of the item, just a <strong>reference</strong> to it.</p>
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    1. COthank you but I was wondering if u can explain it in more basic terms please? i am considering the second option
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    2. CODone :) You really want option #1 by the way.
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    3. COI know but when I stopped the ReadFromFile class being static, nothing worked. Ive forgotten the reason I made it static now
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