How to use NSAssert in iOS

Hi Guys,

In this post we’ll look at how you can use NSAssert in iOS, specifically the best practices or Do’s and Don’ts when using this function. First let’s look at the recommended practices or the Do’s.

How to use NSAssert in iOS – the Do’s

You can use the NSAssert command in your function to make sure a certain condition does not occur or a certain value isn’t passed to the function that may cause problems in your app. For example, if you want a parameter in your method/function to always be a string, you can use the NSAssert command to make sure that it is, otherwise the app will break without going any further. By using NSAssert, you will also be able to track the issue better, making it easier to debug.

Let’s look at an example.

Here, if you don’t pass a string as a parameter your app will break. Thus by using the NSAssert function here you can basically nip the issue in the bud. Additionally, you can provide a description with the NSAssert function as well, which will help explain its use during code reviews or debugging sessions. For example:

Now let’s look at the Don’ts.

How to use NSAssert in iOS – the Don’ts

You must make sure that you never assign a value inside the NSAssert function because if you do, the function won’t get called in Release mode. Take a look at the sample code below.

In the above example, if we assign a value inside NSAssert, then ‘aString’ will get populated in debug mode but not in release mode. We recently made the same mistake while working on a project. We had assigned a value inside NSAssert and as a result, our app started to crash at random. It took us a couple of days to identify the value assignment inside the NSAssert function as the cause.

If you follow these guidelines you’ll save yourself a lot of hassle and debugging time.

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