Bundling resources

Go based applications are usually built as a single binary executable, and this is the same for Fyne applications. A single file makes it easier to distribute install our software. Unfortunately GUI applications typically require additional resources to render the user interface. To manage this challenge a Go application can bundle assets into the binary itself. The Fyne toolkit prefers the use of “fyne bundle” as it has various benefits that we will explore below.

The basic approach to bundle an asset is to execute the “fyne bundle” command. This tool has various parameters to customise the output, but in it’s basic form the file to bundle will be converted into Go source code that can be built into your application.

$ ls
image.png	main.go
$ fyne bundle -o bundled.go image.png
$ ls
bundled.go	image.png	main.go
$

The contents of bundled.go will be a list of resource variables that we can then access in our code. For example the code above will result in a file that includes the following:

var resourceImagePng = &fyne.StaticResource{
	StaticName: "image.png",
	StaticContent: []byte{
...
	}}

As you see the default naming is “resource<Name>.<Ext>”. The name and package used in this file can be customised in command parameters. We can then use this name to, for example, load an image on our canvas:

img := canvas.NewImageFromResource(resourceImagePng)

A fyne resource is just a collection of bytes with a unique name, so this could be a font, a sound file or any other data you wish to load. Also you can bundle many resources into a single file using the -append parameter. If you will be bundling many files it is recommended to save the commands in a go:generate header in one of your go files (not bundled.go):

//go:generate fyne bundle -o bundled.go image1.png
//go:generate fyne bundle -o bundled.go -append image2.png

If you then change any assets or add new ones then you can update this header and run it with “go generate” to update your bundled.go file. You should then add bundled.go to version control so others can build your app without needing to run “fyne bundle”.