How do I fix object reference not set to an instance of an object.

Question

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Im try to read data from xml file with format like this:

XML

<npc_templates>	
	<npc_template npc_id="280001">
		<equipment>
			<item>100000005
			<item>100000006

What I have tried:

And im trying with this code to read equipment/item elements:

C#

public class NpcTemplate
    {
        [XmlAttribute("npc_id")]
        public int npc_id;
        
        [XmlElement("equipment")]
        public NpcEquippedGear equipment;
    }

and NpcEquippedGear class:

C#

public class NpcEquippedGear : IEnumerable<KeyValuePair<EquipmentSlot, ItemTemplate>>
    {
        [XmlElement("item")]
        public ItemTemplate[] items2;

        public Dictionary<EquipmentSlot, ItemTemplate> items;
        public int mask;
        public NpcEquippedGear()
        {
        }

        public void Add(object o)
        {

        }

        public int getItemsMask()
        {
            if (items == null)
                init();
            return mask;
        }

        public void init()
        {
            lock(this)
            {
                if (items == null)
                {
                    items = new Dictionary<EquipmentSlot, ItemTemplate>();
                    foreach (ItemTemplate item in items2)// Error Object reference not set to an instance of an object.
                    {
                        if (items[item.EquipmentSlot] == null)
                        {
                            items.Add(item.EquipmentSlot, item);
                            mask |= (int)item.EquipmentSlot;
                        }
                    }
                }
            }
        }

        public ItemTemplate GetItem(EquipmentSlot slot)
        {
            return items != null ? items[slot] : null;
        }

        public IEnumerator GetEnumerator()
        {
            return GetEnumerator();
        }

        IEnumerator<KeyValuePair<EquipmentSlot, ItemTemplate>> IEnumerable<KeyValuePair<EquipmentSlot, ItemTemplate>>.GetEnumerator()
        {
            return items.GetEnumerator();
        }
    }

That all i try but while run program its tell mw error

C#

Object reference not set to an instance of an object.

at NpcEquippedGear class foreach loop

Posted 26-Nov-16 2:59am

EADever

Updated 26-Nov-16 6:33am

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Comments

Richard MacCutchan 26-Nov-16 10:19am

Because you never initialised items2 to reference anything.

3 solutions

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OriginalGriff · Accepted Answer · 2016-11-26T03:44:00

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!

EADever · Accepted Answer · 2016-11-26T06:33:00

Thanks about your help guys.
Im resolved my issue by recode NpcEquippedGear class

C#

public class NpcEquippedGear
    {
        [XmlElement("item")]
        public int[] items;
        private Dictionary<EquipmentSlot, ItemTemplate> dicItems;
        private int mask;
        public int getItemsMask()
        {
            if (dicItems == null)
                init();
            return mask;
        }
        private void init()
        {
            lock (this)
            {
                if (dicItems == null)
                {
                    dicItems = new Dictionary<EquipmentSlot, ItemTemplate>();
                    foreach (int itemId in items)
                    {
                        ItemTemplate item = Datastore.ItemsById[itemId];
                        if (!dicItems.ContainsKey(item.EquipmentSlot))
                        {
                            dicItems.Add(item.EquipmentSlot, item);
                            mask |= (int)item.EquipmentSlot;
                        }
                    }
                }
            }
        }
        public ItemTemplate GetItem(EquipmentSlot slot)
        {
            return dicItems != null ? dicItems[slot] : null;
        }
    }

Mohtshm Zubair · Accepted Answer · 2016-11-26T03:49:00

Solution 2

Currently u've

C#

foreach (ItemTemplate item in items2)// Error Object reference not set to an instance of an object.

just put this line

if(items2 !=null)

like this

C#

if(items2 !=null)
foreach (ItemTemplate item in items2)// Error Object reference not set to an instance of an object.

It will solve your null exception but it is always good to initialize Arrays or List within contructor or use Initialize method convention

Plz mark the issue resolved!!!!

Posted 26-Nov-16 3:49am

Mohtshm Zubair

Comments

Richard MacCutchan 26-Nov-16 10:19am

No it will just mask it.

EADever 26-Nov-16 11:18am

But problem is im get only equipment data of npc_id that i give at the question. its must return not null, but after i check by code if (items2 != null) {} else {items2 return null}

How do I fix object reference not set to an instance of an object.

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