Now you can use the image in the viewer. For example, if you add button_close.png to drawable, you could use 'button_close' in leadingNavButtonIcon.
iOS
After pods has been installed, open the .xcworkspace file for this application in Xcode (in this case, it's Runner.xcworkspace), and navigate through the list below. This would allow you to add resources, in this case, an image, to your project.
"Project navigator"
"Runner" (or the app name)
"Build Phases"
"Copy Bundle Resources"
"+".
Now you can use the image in the viewer. For example, if you add button_open.png to the bundle, you could use 'button_open.png' in leadingNavButtonIcon.