Check if var da/dtCounts has been assigned before doing anything

Question

How would I check if da and dtCounts is null before assigning it to a new object?

        var da = new MySqlDataAdapter(cmd);
        var dtCounts = new DataTable();
        da.Fill(dtCounts);

`da` will not be null if you construct it... same with `dtCounts`.. — grmbl, Feb 03 '15 at 19:51
Disregard my comment above.You could check for the return value of da.Fill(dtCounts) because it returns a int. — grmbl, Feb 03 '15 at 19:55
possible duplicate of [How to check a var for null value?](http://stackoverflow.com/questions/10753661/how-to-check-a-var-for-null-value) — void, Feb 03 '15 at 19:58

score 2 · Accepted Answer · answered Feb 03 '15 at 19:57

You can't use var in this scenario. Here's a simple example...

MySqlDataAdapter da;
DataTable dtCounts;

// Other code here...

if (da == null)
    da = new MySqlDataAdapter(cmd);

if (dtCounts == null)
    dtCounts = new DataTable();

da.Fill(dtCounts);

score 0 · Answer 2 · answered Oct 12 '16 at 21:48

Another way to do that is using the C# Null-coalescing Operator ?? It returns the left-hand operand if the operand is not null; otherwise it returns the right hand operand. So your code can look like:

MySqlDataAdapter da;
DataTable dtCounts;

// Other code here...

da = da ?? new MySqlDataAdapter(cmd);
dtCounts = dtCounts ?? new DateTable();

da.Fill(dtCounts);

Check if var da/dtCounts has been assigned before doing anything

2 Answers2