capabilities API – Extending Qlik

A third way to run a reload from a Qlik Sense mashup

Back in 2016 I wrote a post on running a reload from a Qlik Sense mashup. To recap, I described two ways:

call the Engine API method doReload(). Use this in Qlik Sense desktop, since it’s the only method available.
use the repository call App reload optionally with the help of the callRepository method. This is of course only relevant in a server installation.

You’ll find code examples in my original post, and also how to know if you are running in server or desktop.

What happens when you use /app/reload ?

While this method works well in some scenarios, like when you just want to run one reload of an app ASAP, it has some limitations. Behind the scenes Qlik will create a very simple task for you, and try to start it immediately. The task will look like this:

Very basic, just an app, a name, an the default Task session timeout of a day (or 1440 minutes). No triggers, since the task is started by the REST call, no tags, no custom properties. And, perhaps most important, no retries. This means that if you create a series of reloads this way, most likely only the first few will succeed, the rest will fail since there is no engine instance available.

Another method to start a reload

But there is another way to do it. You can easily create the Task yourself, and set whatever parameters you need. Qlik Sense QRS API is really easy to work with, and the callRepository method can help you by fixing the xrfkey and wrapping the call in a javascript Promise. So creating a reload task can be made as simply as this:

This will create the reload task the way we want it and return the id for the task, whish we can use to start it. That’s just another call to the Repository like this:

And that’s it. A little more code than the second method, but much more control over what we get.

Adding alternate state support to your Qlik Sense extension

One of the more advanced feature in QlikView is alternate state. It alllows you to have several different selections active at the same time. With set analysis expressions you can then combine your selection sets to gain valuable insights.

While alternate states are not exposed in the built-in Qlik Sense client, you can easily add them to your custom extension with just a few lines of code. Let’s see how.

Step 1: add a property panel field

The qStateName property already exists (check the Qix Engine API), so a first step is to map it to the property panel. Lets create a new section under “Addons”:

This assumes a HyperCube, $ is the default state which is always there. This is already enough for alternate state to work in your extension. If you enter a valid alternate state name in the property panel your extension will be connected to it. Problem is there has to be an alternate state in the app, and you need to know it’s name. Lets do something about that.

Step 2: add a listbox with existing alternate states.

Lets convert our property panel to a dropdown list, where the app developer can choose what state the object should be connected to. We do this by setting the component to ‘dropdown’ and adding a function to return the options:

Alternate states ar listed in the app layout structure, so we need to get the app layout and format the states in the format the property panel dropdown wants. The default state ‘$’ is not in the list, so we need to add that ourselves. For this to work you need to have the qlik module available in your extension.

Now you will have a dropdown list in your extension property panel, something like this:

Still doesn’t look much, does it… But it does it’s job. Now we just need a way to create those alternate states.

Step 3:Creating the alternate states

Well, actually you need to do this first. But there are different ways to achieve this:

there are extensions for this
you could do it in Engine API explorer, since its really a one-time thing
or, you could add it to the property panel.

The property panel is not really meant for this, since we are not updating the object properties, but the app properties, but still it’s pretty easy to do. You can add something like this to the property panel:

It’s really not more complicated than that. You will get an inputfield in the propertypanel. If the user writes anything in that field, an alternate state will be created. It will then show up in the listbox, so you can use it in your extension.

Conclusion

It’s really not at all difficult to add alternate state support to your extension. Probably you should do something to show the user that this chart belongs to an alternate state: you can use the header for that, or add some styling or an icon for charts that are in another state. I’ll leave that for you.

Accessing system data and variables in a Qlik Sense extension

Sometimes when you are building a Qlik Sense extension you need to get access to system data. This is espescially true if you are trying to build something a bit more generic. Perhaps you need a list of fields, or dimensions, or measures. Or you need to work with variables.

If you are new to Qlik Sense development you might look in the API documentation for methods to get the data you need. Don’t do that!! Qlik Sense extension model is based on the idea that you use one Generic Object, described in the extensions initialProperties, and modified by the user in the property panel, and possibly programmatically (but that’s really advanced). So while using the API methods to get additonal data is the approach to use in mashups or Web apps that access Qlik data, you should avoid using them in a masup.

Why you shouldn’t

If you do use these api calls in your extension, you will get problems:

you might easily get a memory leak, or a ‘Generic Object leak’, where you create lots of Generic Objects
you can easily lose contral of all callback functions running when the generic objects are revalidated
if the user makes a snapshot, the API calls will access the latest version of the data, not the one in the snapshot and possibly give the wrong data
if the user tries to export your extension to PDF or Excel it might break, since the service responsible for those export does not have access to live data, only to the snapshot

If you absolutely must use these calls, you should at least turn export to PDF and Excel of and not allow snapshots of your extension.

What you should do instead

Luckily there are alternatives. These API calls all create Generic Objects, but since the Generic Object is a very flexible structure, you can actually configure the Generic Object behind your extension to provide the data you need. Here is a little table of what you could use:

You need	Do not use API call	Instead add to initialProperties
List of fields	app.getList("FieldList")	qFieldListDef
List of measures	app.getList("MeasureList")	qMeasureListDef
List of dimensions	app.getList("DimensionList")	qDimensionListDef
List of variables	app.getList("VariableList")	qVariableListDef
Variable value	app.variable.getContent(..)	qStringExpression or qValueExpression

You find a working example of this in my syslist extension just don’t use it, it’s meant as examples of how to get the data and doesn’t really do anything useful. But do grab the initialProperties part you need for your extension.

It looks like this:

When should you use these API calls

Well, no rule without an exception. While you should avoid using these calls in the API for the rendering part of your extension, you should use them in your property panel, if you for example need to provide a list of fields to the user. And in a mashup, they are definitely very useful. And the API has other calls, which you might want to use, but that vill mainly be when the user does something, like clicking a button etc.

Qlik Sense variable extension – new version

Example of Variable use included in the extension

A new version of my Qlik Sense Extension Variable is now available.

No new functionality, but some minor internal changes:

revised build, CSS is no longer a separate file, but bundled in the javascript file
reverted back to using the Capabilities API
some new examples of use

This release is part of the preparation for the certification of the extension. Read more about that here. This extension is however still not certified.