To learn GDK, first you have to understand the basic concepts and UI components. Once you understand these, things will start to make sense. Before i start explaining anything i would like to tell you that the GDK that Google released is just a sneak peak and it has a very limited functionality. This blog is only to explain the main components of the Glass which is essential to know before we start developing for Glass.
Terminologies explained –
Timeline – Timeline is another important UI component of Glass. It consists of multiple cards, in other words, it holds all the card together. User can interact with it using the D-Pad. Swipe right or left on timeline helps user switch between cards quickly.
Touchpad aka D-Pad – This is main medium to interact with the Glass. It supports the following gestures – swipe right, swipe left, swipe up, swipe down, single tap, double tap. It also support multi touch gestures like – double tap, two finger swipe down and up etc. Google recommends to not to use swipe down as Glass use it as a native back button for glass.
Cards – Card is the main UI component of Glass that is used to display information to the user. It takes the whole screen on Glass and at one point of time Glass can have multiple cards placed next to each other. User can scroll between these cards using the Glass D-Pad. There is one home card which contains current time and word phrase “ok glass” on it. There are two types of card than can be created by user’s action – static and live card. All live cards are placed to the left and all static card placed to the right of home card.
Static Card – This card is a static card and user has no control over it. Only the activity or service that creates a static card can delete this card.
Live Card – Live card shows the live content to the user like current weather. Live card gets deleted when Glass feels they are not relevant anymore. You can stop glass from doing so if you place a background service behind the live card to feed it with information. If Glass will notice a live card which is inactive for a specific duration, it will remove it from the timeline.
Menu – The way menus works on Glass is bit different. Menus on Glass are full screen with a transparent background. If an activity has an option menu, it has to be hooked up with activity’s onkeyDown method else there is no way to open an option menu on glass.
Glass UI Theme – Google recommends not to use any theme while creating a native apps for Glass using GDK. If you compile the app with Google Glass GDK Sneak Peak, it will automatically apply the Glass UI theme to your app. But if you have to create your own theme than you should extend the theme called Theme.DeviceDefault.
That’s it for this blog. In next blog i’ll talk about how to create a card and add it to timeline.