C# Checking if Object is Null

Question

I am having trouble with an if statement for checking if an object is null.

I have a webClient go and pull a JSON string from a website in a try/catch. If it errors, it is because the 3 digit country does not exist in the API and I just want to skip it.

Here is my code:

    System.Net.WebClient wc = new System.Net.WebClient();

    RootObject ro;
    try
    {
        string resp = wc.DownloadString("https://restcountries.eu/rest/v2/alpha/" + Row.Code.ToString());

        JavaScriptSerializer js = new JavaScriptSerializer();

        ro = js.Deserialize<RootObject>(resp);
    }
    catch (Exception e)
    { }

    if (ro.Region != null)
    {
        Row.Region = ro.Region;
        Row.SubRegion = ro.Subregion;
    }

RootObject is a class to deserialize to. This works fine.

However, I am getting an error in the if statement that "use of unassigned class 'ro'.

Can someone help me fix this? ro works as expected inside the if?

I have also tried checking a specific node and it is still getting hung up on the 'ro' part.

Also, this is a script component in SSIS.

Thanks

If an error is thrown and the `catch` path is executed `ro` is not initialized. That's why you get this error. — croxy, Feb 15 '19 at 14:49
Then just assign it. What do you want the program to do if it's not assigned? — user202729, Feb 15 '19 at 14:49
I want it to skip and exit. It is basically done if nothing is returned from the API — KeithL, Feb 15 '19 at 14:50
Change RootObject ro to RootObject ro = null; and change ro.Region != null to ro?.Region != null — Murray Foxcroft, Feb 15 '19 at 14:50
Possible duplicate of [Why compile error "Use of unassigned local variable"?](https://stackoverflow.com/questions/9233000/why-compile-error-use-of-unassigned-local-variable) — Selvin, Feb 15 '19 at 15:09

D Stanley · Accepted Answer · 2019-02-15T15:06:39.413

9

It is possible that the try block will never assign a value to ro and thus it will be unassigned outside of try block. To fix that, assign a value:
```
RootObject ro = null;
```

Since ro could be null, you need to check for that in your if statement before you try to access a member:

if (ro != null && ro.Region != null)
{
    Row.Region = ro.Region;
    Row.SubRegion = ro.Subregion;
}

edited Feb 15 '19 at 15:06

answered Feb 15 '19 at 14:55

D Stanley

149,601
11
178
240

Thanks. Solving this was really #1. I also changed the if to just if(ro!=null) and achieved desired results. – KeithL Feb 15 '19 at 15:03

score 6 · Answer 2 · edited Feb 15 '19 at 15:06

Give ro a default value, so change RootObject ro to RootObject ro = null;

and change ro.Region != null to ro?.Region != null to allow for ro being null.

and possibly do something about swallowing that exception.

System.Net.WebClient wc;

RootObject ro = null;
try
{
    wc = new System.Net.WebClient();
    string resp = wc.DownloadString("https://restcountries.eu/rest/v2/alpha/" + Row.Code.ToString());

    JavaScriptSerializer js = new JavaScriptSerializer();

    ro = js.Deserialize<RootObject>(resp);
}
catch (Exception e)
{
    // Log your error
}

if (ro?.Region != null)
{
    Row.Region = ro.Region;
    Row.SubRegion = ro.Subregion;
}

score 4 · Answer 3 · answered Feb 15 '19 at 14:53

The object ro should be initialized ,cause it is called outside the try scope

RootObject ro = null;
try
{
    string resp = wc.DownloadString("https://restcountries.eu/rest/v2/alpha/" + Row.Code.ToString());

    JavaScriptSerializer js = new JavaScriptSerializer();

    ro = js.Deserialize<RootObject>(resp);
}
catch (Exception e)
{ }

if (ro?.Region != null)
{
    Row.Region = ro.Region;
    Row.SubRegion = ro.Subregion;
}

Aars93 · Answer 4 · 2019-02-15T14:56:14.333

3

Initialize ro with RootObject ro = null; and change the if statement to

if (ro?.Region != null)
{
    Row.Region = ro.Region;
    Row.SubRegion = ro.Subregion;
}

This way the statement will check if either ro is null or ro.Region is null

edited Feb 15 '19 at 14:56

answered Feb 15 '19 at 14:51

Aars93

379
4
10

C# Checking if Object is Null

4 Answers4

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