How to implement custom icon in SAPUI5's Shellbar Control? - sapui5

Question

I implemented a functionality so that the users of my SAPUI5 application can change between different SAPUI5 themes. Now I would like to place a button in the existing ShellBar of my app to trigger that functionality from there.
Currently I have a fragment with the following code, which I want to make use of within a simple button in the ShellBar. I tried different things like f.ex. calling it via the avaterPressed attribute from the shellbar, but it looks all messed up - I'd be very happy if someone could help me out here - Thanks!
<core:FragmentDefinition
xmlns="sap.m"
xmlns:core="sap.ui.core">
<Menu itemSelected="onSelectTheme" >
<MenuItem text="Choose Theme">
<items>
<MenuItem key="sap_fiori_3" text="Standard Light" />
<MenuItem key="sap_fiori_3_dark" text="Standard Dark" />
<MenuItem key="sap_hcw" text="High Contrast White" />
<MenuItem key="sap_hcb" text="High Contrast Black" />
</items>
</MenuItem>
</Menu>
</core:FragmentDefinition>
It should look like the "Administrator" button in the following example (Instead of "User Settings" there should be my text "Choose Theme" from the fragment shown above: https://sapui5.hana.ondemand.com/sdk/test-resources/sap/tnt/demokit/toolpageapp/webapp/index.html?sap-ui-theme=sap_horizon#/

Answer 1

If you want to keep using the ShellBar, you can implement the press event on the Avatar and use the ActionSheet for your needs.
https://sapui5.hana.ondemand.com/#/entity/sap.m.ActionSheet/sample/sap.m.sample.ActionSheet

Answer 2

The developers from the linked example don't use the SAPUI5 Control ShellBar, but instead they made use of ToolHeader, which you can also implement within the Control ToolPage.
With ToolHeader, you can simply add a Button wherever you'd like and also call the fragment from f.ex. the profile picture button (shown below).
<tnt:ToolHeader>
<Avatar src="..." press="YOUR_FUNCTION_TO_OPEN_FRAGMENT"/>
</tnt:ToolHeader>