I want to add a button under the tab of my add-in, and clicking on the button should open a URL in a new window or Dialog box. I tried the follows:
after googling about office dev , I found that you can change the action tag to something like
<!-- This is what happens when the command is triggered (E.g. click on the Button). Supported actions are ExecuteFunction or ShowTaskpane. -->
<Action xsi:type="ExecuteFunction">
<FunctionName>doSomethingAndShowDialog</FunctionName>
</Action>
check the following link it might be helpful
https://github.com/OfficeDev/Office-Add-in-Dialog-API-Simple-Example