Monday, July 8, 2019

Building UIs with EASE

You probably used EASE before to automate daily tasks in your IDE or to augment toolbars and menus with custom functionality. But so far scripts could not be used to build UIs. This changed with the recent contribution of the UI Builder module.

What it is all about
The UI Builder module allows to create views and dialogs by pure script code in your IDE. It is great for custom views that developers do not want to put into their products, for rapid prototyping and even for mocking.

The aim of EASE is to hide layout complexity as much as possible and provide a simple, yet flexible way to implement typical UI tasks.

Example 1: Input Form
We will start by creating a simple input form for address data.

loadModule("/System/UI Builder");
createView("Create Contact");

setColumnCount(2);
createLabel("First Name:");
var txtFirstName = createText();
createLabel("Last Name:");
var txtLastName = createText();
This snippet will create a dynamic view as shown below:
The renderer used will apply a GridLayout. By setting the columnCount to 2 we may simply add our elements without providing any additional layout information - a simple way to create basic layouts.

If needed EASE provides more control by providing layout information when creating components:

createView("Create Contact");
createLabel("First Name:", "1/1 >x");
var txtFirstName = createText("2-4/1 o!");
createLabel("Last Name:", "1/2 >x");
var txtLastName = createText("2-4/2 o!");
Creates the same view as above, but now with detailed layout information.
As an example "1/2 >x" means: first column, second row, horizontal align right, vertical align middle. A full documentation on the syntax is provided in the module documentation (Hover over the UI Builder module in the Modules Explorer view).

Now lets create a combo viewer to select a country for the address:
cmbCountry = createComboViewer(["Austria", "Germany", "India", "USA"])
Simple, isn't it?

So far we did not need to react on any of our UI elements. Next step is to create a button which needs some kind of callback action:
createButton("Save 1", 'print("you hit the save button")')
createButton("Save 2", saveAddress)

function saveAddress() {
 print("This is the save method");
}
The first version of a button adds the callback code as string argument. When the button gets pressed, the callback code will be executed. You may call any script code that the engine is capable of interpreting.

The second version looks a bit cleaner, as it defines a function saveAddress() which is called on a button click. Note that we provide a function reference to createButton().

View the full example of this script on our script repository. In addition to some more layouting it also contains a working implementation of the save action to store addresses as JSON data files.

Interacting with SWT controls

The saveAddress() method needs to read data from the input fields of our form. This could be done using
var firstName = txtFirstName.getText();
Unfortunately SWT Controls can only be queried in the UI thread, while the script engine is executed in its own thread. To move code execution to the UI thread, the UI module provides a function executeUI(). By default this functionality is disabled as a bad script executed in the UI thread might stall your Eclipse IDE. To enable it you need to set a checkbox in Preferences/Scripting. The full call then looks like this:
loadModule("/System/UI")
var firstName = executeUI('txtFirstName.getText();');

Example 2: A viewer for our phone numbers

Now that we are able to create some sample data, we also need a viewer for our phone numbers. Say we are able to load all our addresses into an array, the only thing we need is a table viewer to visualize our entries. Following 2 lines will do the job:
var addresses = readAddresses();
var tableViewer = createTableViewer(addresses)
Where readAddresses() collects our *.address files and stores them into an array.

So the viewer works, however we need to define how our columns shall be rendered.
createViewerColumn(tableViewer, "Name", createLabelProvider("getProviderElement().firstName + ' ' + getProviderElement().lastName"))
createViewerColumn(tableViewer, "Phone", createLabelProvider("getProviderElement().phone"))
Whenever a callback needs a viewer element, getProviderElement() holds the actual element.
We are done! 3 lines of code for a TableViewer does not sound too bad, right? Again a full example is available on our script repository. It automatically loads *.address files from your workspace and displays them in the view.

Example 3: A workspace viewer

We had a TableViewer before, now lets try a TreeViewer. As a tree needs structure, we need to provide a callback to calculate child elements from a given parent:
var viewer = createTreeViewer(getWorkspace().getProjects(), getChildren);

function getChildren() {
 if (getProviderElement() instanceof org.eclipse.core.resources.IContainer)
  return getProviderElement().members();
 
 return null;
}
So simple! The full example looks like this:
Example 4: Math function viewer

The last example demonstrates how to add a custom Control to a view.
For plotting we use the Charting module that is shipped with EASE. The source code should be pretty much self explanatory.

Some Tips & Tricks

  • Layouting is dynamic.
    Unlike the Java GridLayout you do not need to fill all cells of your layout. The EASE renderer takes care to automatically fill empty cells with placeholders
  • Elements can be replaced.
    If you use coordinates when creating controls, you may easily replace a given control by another one. This simplifies the process of layouting (eg if you experience with alignments) and even allows a view to dynamically change its components depending on some external data/events
  • Full control.
    While some methods from SWT do not have a corresponding script function, still all SWT calls may be used as the create* methods expose the underlying SWT instances.
  • Layout help.
    To simplify layouting use the showGrid() function. It displays cell borders that help you to see row/column borders.


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