Printing Qlik Sense extensions

From time to time I get questions from Qlik customers and partners with some problem regarding Qlik Sense extensions or mashups. Usually this means a few hours of troubleshooting and hopefully fixing something, fun and interesting. Could be extensions that break when Qlik Sense is upgraded, performance issues or some feature that doesn’t work.

A recurring problem is with printing extension objects. Many customers don’t care whether this works, they don’t use NPrinting or it’s not relevant for their extensions, but some do. And if they have problems, it can be a challenge to solve them if you have never done it before.

How does it work

Qlik Sense uses snapshots for printing. That means what’s printed is not what you see on your screen, but a snapshot of the data in the extension, that is then re-rendered by the rendering engine and eventually printed. There is no live connection to the Qlik Sense engine available during this re-rendering, which means that everything that needs a live connection is not available. That’s why you should always base your rendering only on the layout.

So, a first step is to verify that the extension does not do any calls that require an engine connection in the rendering part (they can be used in the property panel, and in many cases are to fill dropdown lists with content etc). This might require some refactoring to solve and so might take some time, but in most cases this is not the problem.

Waiting for the extension to be ready

A more common problem is that the printing is made before the extension is ready. This might mean that printing works sometimes, but not all of the time. It might also mean that the printout is partial, showing the extension when parts of it are rendered, but not all of it etc.

To solve this you need to return a Promise and make sure it is not resolved until your rendering is complete, something like this:

paint: function ($element, layout) {
  // do your rendering
  return new qlik.Promise(function (resolve, reject) {
    // when rendering is complete, call resolve
    resolve();
    // optionally if rendering fails, call reject 
    reject();
  });
} //end of print function

The Promise supplied by Qlik now follows the standard javascript API (though it looks like it isn’t the standard) unlike in previuos releases where it was essentially angular $p service. I’m afraid that means the code I’ve published earlier in this blog no longer works, the code above is how it should be.