Telling your user that a PhoneGap application is busy

Posted by Michael Nachbaur

Plenty of times in applications, especially on mobile devices, you just need to tell your users to hold their horses and wait while your application processes something in the background.  Maybe you need to query some data from a remote server, save a file to disk, or maybe you just need to do some number crunching.  Whatever the reason, you don't want your user to think the program has crashed if you don't give them some sort of visual feedback that you're busy and they just have to wait a few seconds.

PhoneGap provides a few methods to handle just this task. There's four methods within the Notification class that are of interest.

1. navigator.notification.loadingStart()
2. navigator.notification.loadingStop()
3. navigator.notification.activityStart()
4. navigator.notification.activityStop()

Modal loading messages

Modal loading indicator

The easiest approach to take when making your users wait is to show a modal loading dialog, one that doesn't let the user interact with the application until you're done.  There's a lot less for you, as a developer, to manage when the user isn't allowed to poke around on buttons when you're updating the display.  Asynchronous operations are a lot simpler when you're in control.

The loadingStart() and loadingStop() methods do just this.  They put up a modal semi-transparent layer over top of your application, with a "Loading.." spinner message. You simply call the first method when your application is about to do something, and when it finishes you call the second.

Here's an example of how to use it.  This will load a remote HTML document and place its contents into a node in your PhoneGap application.

Not only does this make it easier to integrate external content into your PhoneGap application, but it guarantees your user is informed that it's actively working. As a final bonus, if your external web site doesn't respond, or if the user doesn't have an Internet connection, the modal loading screen will close after a timeout.

Asynchronous loading messages

Asyncronous activity loading indicator

Sometimes you want to tell your user that the application is busy, but you still want to continue using the app anyway.  If your app doesn't turn off the top statusbar (where the time, reception, and battery status is displayed), you can control the busy indicator from within PhoneGap.  Just like the above example, you just have to call the appropriate PhoneGap JavaScript methods.  In this case, just update the above example with these messages:

navigator.notification.activityStart();
// Do something that might take a while...
navigator.notification.activityStop();

How to use the native Alert dialog in PhoneGap

Posted by Michael Nachbaur

PhoneGap's custom alert notification is nicely customizable

An important part to any application is issuing a simple alert to your user. Whether it's to tell them about an error that just occurred, or if you need to ask them a simple question, giving a message to your user is about the most basic part of any app.

Sadly, when you try to rely on the ever faithful "alert()" function in JavaScript inside a PhoneGap application, you'll notice the alert box it shows is titled with a very unprofessional "index.html" across the top. Not only does it make it obvious that the app they're interacting with is actually HTML-based, but you can't convey the importance of one message or another with a title. Most people only ever read the title anyway, so in order to provide this capability to your application, PhoneGap has an answer for this problem.

Inside PhoneGap there's a class called "Notification" which is used for, well, sending notifications to your user. And, by calling:

navigator.notification.alert(
  message,
  title,
  buttons...,
  options);

Everything, except for the message, is optional. The more arguments you provide, the more you can customize the alert box. For instance, if you don't supply a button label, one single "OK" button will be created. Want to ask a Yes/No question? Simply pass two labels for their respective button names.

Like other functions in PhoneGap, the alert notification can be passed an "options" object that allows you to give it more information, such as an onClick callback.

That example shows how to ask your user what to do in the event of an Internet connection problem.  You'll notice that I've decided to pass two button labels.  In the onClick callback function I supplied in my options argument, I'm checking the "buttonIndex" variable it passes.  This tells your function which button was pressed.  If you want more than 2 buttons, just list multiple labels and it will show as many as can fit on the screen.

A very simple function, but invaluable as a developer resource.  And, more importantly, a very easy and professional way to get feedback from your user.

How to use the ActionSheet in PhoneGap

Posted by Michael Nachbaur

The ActionSheet is a handy control on the iPhone, and is a very intuitive way of getting a multiple-choice answer from a user in a modal but unobtrusive way.

Using it in PhoneGap makes interacting with your user easy, while keeping the display responsive. And as an added bonus, you don't need to update any HTML or CSS to get the buttons to look right. The native iPhone codebase handles it for you.

So the question is, how do you use it effectively? As most Web2.0-style developers are aware, the only sensible way to develop flexible applications that don't bog down the browser is to make your applications behave asynchronously, and make use of callback functions to get feedback from external systems (HTTP requests, users, etc). The ActionSheet on PhoneGap is no different.

The ActionSheet is grouped into the PhoneGap "Dialog" class, and is called like so:

dialog.openButtonDialog(title, buttons..., options);

The title property lets you specify the label to show at the top of the ActionSheet. If you don't want a title, then simply pass in a null value.

The list of buttons is specified as a series of objects, which I'll describe below.

Finally, the options let you customize how the ActionSheet is displayed (via the "style" property) and lets you set an onClick handler for the entire ActionSheet.

The example above illustrates several options of the ActionSheet PhoneGap control.

1. On a per-button basis you can specify your own onClick callback which will be run when that button is pressed.
2. A global onClick handler can be specified in the openButtonDialog options argument, which will get called no matter what button is pressed.
3. You can choose what the appearance of the dialog should be (currently only "opaque" and "translucent" are supported)
4. A button requires a label property, but you can optionally specify a "type" property (can be "normal", "cancel" or "destroy").

The callback functions are simply called with two arguments, the index of the button being clicked, and the label of the button the user clicked on.  So if it's easier for you to work with array indexes, or with text labels, you can easily find out which button was pressed and when.

So go ahead and try out the ActionSheet control.  Either you can use my latest release in my branch of PhoneGap, or you can use these more advanced features once my changes have been merged in with the official branch.