With the possible exception of listening to streaming audio, a user’s interaction with an Android device is primarily visual and tactile in nature. All of this interaction takes place through the user interfaces of the applications installed on the device, including both the built-in applications and any third party applications installed by the user. It should come as no surprise, therefore, that a key element of developing Android applications involves the design and creation of user interfaces.
With the possible exception of listening to streaming audio, a user’s interaction with an Android device is primarily visual and tactile in nature. All of this interaction takes place through the user interfaces of the applications installed on the device, including both the built-in applications and any third party applications installed by the user. It should come as no surprise, therefore, that a key element of developing Android applications involves the design and creation of user interfaces.
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Within this chapter, the topic of Android user interface structure will be covered, together with an overview of the different elements that can be brought together to make up a user interface; namely Views, View Groups and Layouts.
Within this chapter, the topic of Android user interface structure will be covered, together with an overview of the different elements that can be brought together to make up a user interface; namely Views, View Groups and Layouts.
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12.1 Designing for Different Android Devices
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= Designing for Different Android Devices ==
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The term “Android device” covers a vast array of tablet and smartphone products with different screen sizes and resolutions. As a result, application user interfaces must now be carefully designed to ensure correct presentation on as wide a range of display sizes as possible. A key part of this is ensuring that the user interface layouts resize correctly when run on different devices. This can largely be achieved through careful planning and the use of the layout managers outlined in this chapter.
The term “Android device” covers a vast array of tablet and smartphone products with different screen sizes and resolutions. As a result, application user interfaces must now be carefully designed to ensure correct presentation on as wide a range of display sizes as possible. A key part of this is ensuring that the user interface layouts resize correctly when run on different devices. This can largely be achieved through careful planning and the use of the layout managers outlined in this chapter.
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It is also important to keep in mind that the majority of Android based smartphone and tablets can be held by the user in both portrait and landscape orientations. A well-designed user interface should be able to adapt to such changes and make sensible layout adjustments to utilize the available screen space in each orientation.
It is also important to keep in mind that the majority of Android based smartphone and tablets can be held by the user in both portrait and landscape orientations. A well-designed user interface should be able to adapt to such changes and make sensible layout adjustments to utilize the available screen space in each orientation.
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12.2 Views and View Groups
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== Views and View Groups ==
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Every item in a user interface is a subclass of the Android View class (to be precise android.view.View). The Android SDK provides a set of pre-built views that can be used to construct a user interface. Typical examples include standard items such as the Button, CheckBox, ProgressBar and TextView classes. Such views are also referred to as widgets or components. For requirements that are not met by the widgets supplied with the SDK, new views may be created either by subclassing and extending an existing class, or creating an entirely new component by building directly on top of the View class.
Every item in a user interface is a subclass of the Android View class (to be precise android.view.View). The Android SDK provides a set of pre-built views that can be used to construct a user interface. Typical examples include standard items such as the Button, CheckBox, ProgressBar and TextView classes. Such views are also referred to as widgets or components. For requirements that are not met by the widgets supplied with the SDK, new views may be created either by subclassing and extending an existing class, or creating an entirely new component by building directly on top of the View class.
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A view can also be comprised of multiple other views (otherwise known as a composite view). Such views are subclassed from the Android ViewGroup class (android.view.ViewGroup) which is itself a subclass of View. An example of such a view is the RadioGroup, which is intended to contain multiple RadioButton objects such that only one can be in the “on” position at any one time. In terms of structure, composite views consist of a single parent view (derived from the ViewGroup class and otherwise known as a container view or root element) that is capable of containing other views (known as child views).
A view can also be comprised of multiple other views (otherwise known as a composite view). Such views are subclassed from the Android ViewGroup class (android.view.ViewGroup) which is itself a subclass of View. An example of such a view is the RadioGroup, which is intended to contain multiple RadioButton objects such that only one can be in the “on” position at any one time. In terms of structure, composite views consist of a single parent view (derived from the ViewGroup class and otherwise known as a container view or root element) that is capable of containing other views (known as child views).
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Another category of ViewGroup based container view is that of the layout manager.
Another category of ViewGroup based container view is that of the layout manager.
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12.3 Android Layout Managers
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== Android Layout Managers ==
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In addition to the widget style views discussed in the previous section, the SDK also includes a set of views referred to as layouts. Layouts are container views (and, therefore, subclassed from ViewGroup) designed for the sole purpose of controlling how child views are positioned on the screen.
In addition to the widget style views discussed in the previous section, the SDK also includes a set of views referred to as layouts. Layouts are container views (and, therefore, subclassed from ViewGroup) designed for the sole purpose of controlling how child views are positioned on the screen.
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The Android SDK includes the following layout views that may be used within an Android user interface design:
The Android SDK includes the following layout views that may be used within an Android user interface design:
