Скачать или смотреть How to Set Unique IDs for Drawn Features in OpenLayers Without Removal

Learn how to set unique IDs for features drawn in OpenLayers using JavaScript, while preventing unwanted removals after drawing.
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This video is based on the question https://stackoverflow.com/q/72613490/ asked by the user 'user17515752' ( https://stackoverflow.com/u/17515752/ ) and on the answer https://stackoverflow.com/a/72627097/ provided by the user 'Rob' ( https://stackoverflow.com/u/5801610/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license.

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Setting Unique IDs in OpenLayers Drawing Features

If you're developing web applications using JavaScript and OpenLayers, you might encounter a common dilemma: how to assign unique IDs to features without them being removed immediately after drawing. In this post, we're going to take a closer look at this challenge and provide you with a clear solution to implement unique IDs for your drawn features efficiently.

The Challenge

In your application, users can draw various shapes like polygons and circles. However, after integrating a mechanism to assign IDs to these shapes, you may notice that newly drawn features are getting removed as soon as they are created. This can be frustrating, especially when you want your users to draw multiple features and manage them effectively.

Here’s a bit of code that illustrates the initial setup for drawing features:

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

Adding Unique IDs

Your first step was to implement a function that generates unique IDs for each drawn feature. The approach you were using seemed correct at first:

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

However, this code isn't functioning as expected because the uid() function returns another function, meaning every feature ends up getting the same incorrect ID.

The Issue with uid() Function

When you create your uid() function, its output behaves like a function rather than an ID number. As a result, whenever you attempt to set an ID for the drawn features, they all receive the same function reference instead of unique values.

To visualize this, if you log the generated ID to the console, you'll see it shows that it's a function, not a number. Here’s how the uid() function looks:

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

The Solution

To fix this issue and give each feature a truly unique ID, you need to modify how you call the uid() function. Instead of calling it every time in your drawend event, you should first create an instance of the function. This allows you to store the function reference and generate unique IDs correctly:

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

Retrieve the Unique ID

Once you've assigned unique IDs to your drawn features, retrieving these IDs later is simple. You can use the following method:

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

Conclusion

Implementing unique IDs for drawn features in OpenLayers enhances your application's interactivity and functionality. Ensure you use the uid() pattern correctly by creating an instance and invoking it to obtain unique numbers for IDs. This approach not only resolves the initial problem but also makes it easier to manage the features drawn on your map.

With these tips, you'll be able to develop a more engaging experience for your users while drawing and managing features in OpenLayers.

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