How do you explain image and memory performance problems in Flutter?

Short answer

Separate the file size from the size of the decoded image in memory, and use appropriate caching and resizing for display instead of loading a huge asset for every device.

Explanation

Watch memory and raster time when showing many images, and define a cache policy and lifecycle. Improving image quality or compressing it is not enough if the decode dimensions are much larger than its place on the screen.

Common mistakes

• Assuming a small JPEG file means small memory consumption.
• Removing all caching and then re-downloading images on every rebuild.

Follow-up questions

• When do you use ListView.builder instead of building a whole list?

Sources

• Flutter docs — Performance best practices
• Flutter API — Image constructor
• Flutter API — ResizeImage