Windows application mdi parent form error

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This is my code but i got a error

C#

Object reference not set to an instance of an object.

C#

adminmdipanel adpanel = new adminmdipanel();
                       adpanel.Show();


                       usercreation uc = new usercreation();
                       uc.find.Visible = false;

                       uc.MdiParent = this.MdiParent;
                       uc.MdiParent.Show();
                       uc.Focus();

how to solve this error give me any one ideas

What I have tried:

windows application mdi parent form error

Posted 14-May-16 5:40am

Boopalslm

Updated 14-May-16 10:31am

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Boopalslm 14-May-16 12:29pm

i got now another error

Form that was specified to be the MdiParent for this form is not an MdiContainer.
Parameter name: value

how to solve this error

3 solutions

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OriginalGriff · Answer 1 · 2016-05-14T05:52:00

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!

Karthik_Mahalingam · Answer 2 · 2016-05-14T06:50:00

Solution 2

Go to your main form of your application and open the properties window ( F4 or right click -> properties )
find IsMdiContainer property and set it as true

Posted 14-May-16 6:50am

Karthik_Mahalingam

Comments

Boopalslm 14-May-16 13:00pm

main form means which form

Boopalslm 14-May-16 13:04pm

now i was set true but click mdi panel menu strip my form error is came

Form cannot be both an MDI child and MDI parent.
Parameter name: value

Karthik_Mahalingam 14-May-16 13:10pm

make only one from as MDI parent and rest all make it as child form

Karthik_Mahalingam 14-May-16 13:06pm

the form which you want to make it as parent for all

Boopalslm 14-May-16 13:08pm

yes

Sergey Alexandrovich Kryukov · Answer 3 · 2016-05-14T10:31:00

You did not show where the exception with the message "Object reference not set to an instance of an object" is thrown.

Not to worry. This is one of the very easiest cases to detect and fix. It simply means that some member/variable of some reference type is dereferences by using and of its instance (non-static) members, which requires this member/variable to be non-null, but in fact it appears to be null. Simply execute it under debugger, it will stop the execution where the exception is thrown. Put a break point on that line, restart the application and come to this point again. Evaluate all references involved in next line and see which one is null while it needs to be not null. After you figure this out, fix the code: either make sure the member/variable is properly initialized to a non-null reference, or check it for null and, in case of null, do something else.

Please see also: want to display next record on button click. but got an error in if condition of next record function "object reference not set to an instance of an object".

Sometimes, you cannot do it under debugger, by one or another reason. One really nasty case is when the problem is only manifested if software is built when debug information is not available. In this case, you have to use the harder way. First, you need to make sure that you never block propagation of exceptions by handling them silently (this is a crime of developers against themselves, yet very usual). The you need to catch absolutely all exceptions on the very top stack frame of each thread. You can do it if you handle the exceptions of the type System.Exception. In the handler, you need to log all the exception information, especially the System.Exception.StackTrace:
http://msdn.microsoft.com/en-us/library/system.exception.aspx,
http://msdn.microsoft.com/en-us/library/system.exception.stacktrace.aspx.

The stack trace is just a string showing the full path of exception propagation from the throw statement to the handler. By reading it, you can always find ends. For logging, it's the best (in most cases) to use the class System.Diagnostics.EventLog:
http://msdn.microsoft.com/en-us/library/system.diagnostics.eventlog.aspx.

Now, I want to give you a totally different idea: who needs MDI, ever? Why torturing yourself and scaring off your users?
Do yourself a great favor: do not use MDI at all. You can do much easier to implement design without it, with much better quality. MDI is highly discouraged even by Microsoft, in fact, Microsoft dropped it out of WPF and will hardly support it. More importantly, you will scare off all your users if you use MDI. Just don't. Please see:
http://en.wikipedia.org/wiki/Multiple_document_interface#Disadvantages,
How to Create MDI Parent Window in WPF?.

I can explain what to do instead. Please see my past answers:
How to Create MDI Parent Window in WPF?,
Question on using MDI windows in WPF,
MDIContainer giving error,
How to set child forms maximized, last childform minimized.

Good luck,

—SA

Windows application mdi parent form error

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