Object Reference not set to an instance Exception

Question

I have a DataGridView which is bound to a datasource. I have also a TextBox to filter the records. In TextChanged event of the textbox I have a this line of code: i bind the gridview through designview of the form drag the gridview and choose datasource ... and then the member table.

(gvSideMember.DataSource as DataTable).DefaultView.RowFilter = 
    string.Format("F_NAME LIKE '%{0}%'", textSearch.Text);

But when I try to filter records it shows me that object reference is not set to an instance. The datasource has records. I don't know what's going on, kindly guide me, help will be appreciated.

If DataSource is not a DataTable, then (DataSource as DataTable) returns null. — Roy Dictus
– Roy Dictus, Commented Dec 6, 2013 at 10:11
yes it is the reason how to create the datasource as table i simply bind it through design not programingly — buddy
– buddy, Commented Dec 6, 2013 at 10:13
Never use the as keyword if you are not prepared to accept that the result might be null! If you say (source as Table).View you are not accepting that the as operator might give null. In that case you should use cast syntax, ((Table)source).View, instead. When the former fails, you get an non-informative exception message Object reference not set to an instance. But with the latter, you get something like Unable to cast object of type 'INTERESTING_INFO' to type 'Table', and that helps you understand what you do. So in short: Avoid as in such cases. — Jeppe Stig Nielsen
– Jeppe Stig Nielsen, Commented Dec 6, 2013 at 10:41

Tobias Ramforth · Accepted Answer · 2013-12-16 11:53:55Z

1

You are using the as keyword. Could it be that gvSideMember.DataSource, although having records, is not of the type DataTable, so that (gvSideMember.DataSource as DataTable) is null?

edited Dec 16, 2013 at 11:53

answered Dec 6, 2013 at 10:13

Tobias Ramforth

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buddy Over a year ago

i think datasource is not a table it is through the dataset

Roy Dictus · Accepted Answer · 2013-12-06 10:46:37Z

1

If DataSource is not a DataTable, then (DataSource as DataTable) returns null.

What you can do, for instance, is this:

var src = gvSideMember.DataSource;

Put a breakpoint AFTER that line, then when you hit it, QuickWatch src in Visual Studio to see its type and contents.

Then you can update your source code to use the proper type of DataSource.

EDIT If the DataSource is a DataSet, it will contain one or more tables. If it contains a single table, that is easy to retrieve:

var src = (DataSet) gvSideMember.DataSource;
var table = src.Tables[0];

But if it contains more tables, you can retrieve it with the right number (0, 1, ...) or the name:

var table = src.Tables["MyTable"];

edited Dec 6, 2013 at 10:46

answered Dec 6, 2013 at 10:19

Roy Dictus

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1 Comment

Jeppe Stig Nielsen Over a year ago

Avoid as when you require the cast to succeed. Then you will see the actual type already in the exception text, and you won't have to debug to find that type.

Fenton · Accepted Answer · 2013-12-06 10:11:38Z

0

You can test nullity before the statement - in the example below I'm just logging that they are null, so you'll still get the error, but you can use these checks to either decide not to perform the operation or supply defaults etc.

if (gvSideMember == null) {
    Debug.WriteLine("gvSideMember is null");
}

if (textSearch == null) {
    Debug.WriteLine("textSearch is null");
}

(gvSideMember.DataSource as DataTable).DefaultView.RowFilter = 
    string.Format("F_NAME LIKE '%{0}%'", textSearch.Text);

You can test anything that could possibly be null - even (gvSideMember.DataSource as DataTable).DefaultView if you like.

answered Dec 6, 2013 at 10:11

Fenton

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