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GWT Shortcut-Trapper

Simple GWT library for handling keyboard shortcuts.

View the Demo

Getting Started

  1. Include Vertispan Shortcut-Trapper in your application
<dependencies>
  <dependency>
    <groupId>com.vertispan.shortcut</groupId>
    <artifactId>gwt-shortcut-trapper</artifactId>
    <version>LATEST</version>
    <scope>provided</scope>
  </dependency>
</dependencies>
  1. Include Shortcut-Trapper in your gwt.xml
<inherits name="com.vertispan.lib.shortcuttrapper.ShortcutTrapper"/>
  1. Add some shortcuts to listen for

Shortcuts are added by using modifier+key combinations, such as ctrl+c, alt+a, shift+f.

private void initKeyboardShortcuts() {
    // The library supports global shortcuts 
    //   - listens as the document level
    ShortcutTrapper globalTrapper = ShortcutTrapper.getGlobal();
    globalTrapper.bind("ctrl+p", this::onPrint);
    
    // The library also supports scoping shortcuts to other DOM elements
    ShortcutTrapper editorShortcuts = ShortcutTrapper.getInstance(editorElement);
    editorShortcuts.bind("ctrl+c", this::onCopy);
}

private boolean onPrint(KeyboardShortcutEvent event) {
    console.log("Handle custom print dialog");
    return false; // stops further bubbling and prevents default
}

private boolean onCopy(KeyboardShortcutEvent event) {
    console.log("Custom copy code");
    return false; // stops further bubbling and prevents default
}

Sequence Capture

This library also supports gmail-like sequence shortcuts.

ShortcutTrapper globalTrapper = ShortcutTrapper.getGlobal();
globalTrapper.bind("g i", this::onNavInbox);

// emacs-like bindings
globalTrapper.bind("ctrl+x ctrl+f", this::onOpenFile);
globalTrapper.bind("ctrl+x h", this::onMarkWholeBuffer);
globalTrapper.bind("ctrl+x r m", this::onCreateBookmark);
// secret codes... 
globalTrapper.bind("up up down down left right left right b a enter", this::onKonami);

Shortcut names

For many of the shortcut names, we have alternatives/aliases to make it easier to code with. All of these can be used in the binding and will be normalized, so using up or uparrow will both perform the same binding.

Here is a list of them:

  • up - uparrow
  • down - downarrow
  • left - leftarrow
  • right - rightarrow
  • option - alt
  • command - meta
  • return - enter
  • escape - esc
  • plus - +
  • mod - this one will be either "meta" or "ctrl";
    • "meta" if navigator platform matches iphone, mac, ipad, ipod

Information about the KeyboardShortcutEventHandler

It was mentioned briefly above in the getting started section, but should be mentioned again about the handler method return type. The KeyboardShortcutEventHandler.onShortcut() returns boolean. Returning false will prevent default browser behavior and stop event bubbling. Returning true makes the handler more of a 'peek' and allows other handlers above to receive the event as well.

This may seem obvious with certain shortcut bindings that overlap with browser, such as ctrl+p, ctr+r, f5, etc, but can also be handy when orchestrating multiple ShortcutTrapper instances in nested divs.

For example, in the following DOM structure, we have a simple nesting of div elements.

<div id="grandparent">
  <div>
    <div id="grandchild"/>
  </div>
</div>

We can bind identical shortcuts to both grandparent and grandchild elements. We can allow certain events to bubble if we also want the grandparent handler to be triggered as well.

private void initKeyboardShortcuts(){
    ShortcutTrapper grandparentTrapper = ShortcutTrapper.getInstance(grandparentEl);
    ShortcutTrapper grandchildTrapper = ShortcutTrapper.getInstance(grandchildEl);

    grandparentTrapper.bind("ctrl+c", this::onGrandparentCopy);
    grandchildTrapper.bind("ctrl+c", this::onGrandchildCopy);
}

private boolean onGrandparentCopy(KeyboardShortcutEvent event) {
    console.log("Copy in Grandparent");
    return false; // stops further processing
}
    
private boolean onGrandchildCopy(KeyboardShortcutEvent event) {
    console.log("Copy in Grandchild");
    return true; // allow to bubble
}

When focus is within the grandchild element, and the user presses ctrl+c, the console will log both:

Copy in Grandchild
Copy in Grandparent

Specify Event Type

For the most part, Shortcut-Trapper can determine, from the binding combo, what event to listen on; keydown, keyup, keypress. However, if you want to bind the shortcut on a specific event type, this can be done through the binding

shortcutTrapper.bind("ctrl+c", this::onCopy, BindType.KEYDOWN);

Other Functions

Pausing Handlers

A ShortcutTrapper instance can be paused by enabling/disabling. By disabling a ShortcutTrapper, it will not listen for combo sequences and fire events.

shortcutTrapper.setEnabled(false);   // stops listening
shortcutTrapper.setEnabled(true);    // resumes listening

Get All Bindings

All configured combo bindings can be retrieved as a map. Any changes to the resulting Map will not impact the actual bindings. This is more for informational purposes.

Map<String, KeyboardShortcutEventHandler> bindings = shortcutTrapper.getBindings();

Delete All Shortcuts

All combinations bound to a ShortcutTrapper can be removed by using the removeAll method.

shortcutTrapper.removeAll();

Remove Specific Binding

Individual bindings can be removed by passing the exact same combo String.

shortcutTrapper.unbind("ctrl+c");