Скачать или смотреть Resolving Object Reference Not Set Error When Using Web Services in Visual Studio 2017

Learn how to troubleshoot the `Object Reference Not Set` error in your Visual Studio 2017 web services integration, specifically for transfer order creation in a Windows Forms application.
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Understanding the Object Reference Not Set Error in VS2017 Web Services

When developing applications in Visual Studio 2017, it's common to encounter various errors, especially when integrating web services. A frequently encountered error is the notorious Object Reference Not Set to an Instance of an Object. In this article, we will explore a specific scenario involving this error in a web services integration tasked with creating transfer orders for a production plant.

The Problem

You are working on a Windows Forms application for an ordering system and attempting to implement a web service to create transfer orders in SAP. After successfully testing the web service using SOAP, you face an error when trying to set parameters for the request, specifically with the RequiredQuantity object. Let's dive into why this error occurs and how to resolve it.

You have the following essential lines of code to set the RequiredQuantity:

[[See Video to Reveal this Text or Code Snippet]]

However, this results in an Object Reference Not Set error. The core issue lies in the fact that the RequiredQuantity property has not been instantiated before trying to assign values to it.

The Solution: Instantiating Required Objects

To resolve the problem, you must first create an instance of the RequiredQuantity object before attempting to set its properties. Here's how you can do that:

Step 1: Instantiate the Object

Before using the RequiredQuantity, you need to create a new instance of it in your code. Here's the modified snippet:

[[See Video to Reveal this Text or Code Snippet]]

Why the Instantiation is Necessary

The Object Reference Not Set error arises because you're trying to set properties on a sub-object (in this case, RequiredQuantity) that has not been instantiated—i.e., it currently is null. When you create an instance of RequiredQuantity, you effectively provide a reference that allows you to assign values to unitCode and Value.

Understanding the Error in Context

Here’s a breakdown of why this specific error occurs:

Complex Objects vs. Simple Types: The properties like WarehouseID and MaterialNumberID are simple strings and do not require instantiation. They can be directly set, but more complex types (like RequiredQuantity) must first be instantiated.

WSDL Generation: The WSDL (Web Services Description Language) generated classes can include multipart objects. In such cases, you'll need to ensure that you instantiate those objects to avoid null references.

Conclusion

By instantiating the RequiredQuantity object prior to attempting to set its properties, you will prevent the Object Reference Not Set to an Instance of an Object error in your Visual Studio 2017 project. Remember, whenever you encounter this error, take a moment to check if you're dealing with an uninstantiated object. This simple step can save you lots of debugging time and energy, allowing you to focus on enhancing your application's functionality.

Now you can proceed confidently with your web service integration! If you have any further questions or need additional support, feel free to reach out.