The solution may be as follows.
Add the UI:field
attribute in the markup:
<g:Image url='{res.user1.getURL}' ui:field="imageUser1" />
Then, change the attribute value by this way:
@UiField Image imageUser1;
imageUser1.setVisible(true/ false);
It is also possible dynamically change the image URL -
user1.setUrl(offlineImg.getUrl());
See also: