How to Call a Composable Function from an onClick in Jetpack Compose

Discover how to effectively call a `Composable` function from an `onClick` event in Jetpack Compose and avoid common errors.
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This video is based on the question stackoverflow.com/q/78166970/ asked by the user 'Joelskoldator123' ( stackoverflow.com/u/21868303/ ) and on the answer stackoverflow.com/a/78166990/ provided by the user 'BenjyTec' ( stackoverflow.com/u/8331157/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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How to Call a Composable Function from an onClick in Jetpack Compose

Jetpack Compose has revolutionized the way we build UI in Android apps, but it does come with its own unique set of rules and patterns. One common issue that developers face is trying to call a Composable function directly from an onClick event. This can lead to errors such as "Composable invocations can only happen from the context of a @Composable function." In this post, we will dissect this problem and explore how to handle it effectively.

The Problem

When you create a UI element, such as a Card, and assign an onClick event handler, you may want to show a Composable function upon clicking that element. However, if you attempt to call a Composable function directly inside the onClick event, you will get the error mentioned above. Let's review the original snippet causing the error:

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

In this example, the Camera.Preview() function is a Composable, but calling it directly in the onClick context is not allowed.

The Solution

To solve this issue, we can manage the visibility of the Composable function by using state variables. Here is a structured way to implement this solution:

Step 1: Create a State Variable

To control when the Preview function is shown, we need to declare a state variable that tracks its visibility. We can do this using remember and mutableStateOf.

Step 2: Modify the Composable Function

Here’s a revised version of our main Composable function that incorporates a clickable Card and uses the state variable to manage visibility:

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

How It Works

State Management: By declaring showPreview as a state variable, we enable the UI to be responsive to changes.

Conditional Rendering: The if (showPreview) statement effectively controls whether the Preview composable is displayed or not.

Recomposition: When the Card is clicked, showPreview is set to true, which triggers a recomposition of the UI and renders the Preview.

Best Practices

Avoid Object Wrapping: Place Composable functions as standalone functions instead of wrapping them in objects. It’s best practice to keep them accessible, making it easier for other parts of your code to invoke them.

By following these steps, you can call a Composable function within an onClick event without running into errors. This approach helps maintain a clean and efficient flow in your Jetpack Compose UI design.

Conclusion

Handling Composable functions correctly in Jetpack Compose might seem challenging at first, but with state management and conditional rendering, you can avoid common pitfalls. Now you have a clear method to call a Composable function from an onClick event. Happy coding!