When creating an Android application, we have to be aware of the existence of multiple screen sizes and screen resolutions. It is important to check how our layouts are displayed in different screen configurations. To accomplish this, Android Studio provides a functionality to change the layout preview when we are in the design mode.
We can find this functionality in the toolbar, the device definition option used in the preview is by default Nexus 4. Click on it to open the list of available device definitions.
Try some of them. The difference between a tablet device and a device like the Nexus one are very notable. We should adapt the views to all the screen configurations our application supports to ensure they are displayed optimally.
The device definitions indicate the screen inches, the resolution, and the screen density. Android divides into ldpi, mdpi, hdpi, xhdpi, and even xxhdpi the screen densities.
- ldpi (low-density dots per inch): About 120 dpi
- mdpi (medium-density dots per inch): About 160 dpi
- hdpi (high-density dots per inch): About 240 dpi
- xhdpi (extra-high-density dots per inch): About 320 dpi
- xxhdpi (extra-extra-high-density dots per inch): About 480 dpi
The last dashboards published by Google show that most devices have high-density screens (34.3 percent), followed by xhdpi (23.7 percent) and mdpi (23.5 percent). Therefore, we can cover 81.5 percent of the devices by testing our application using these three screen densities. Official Android dashboards are available at http://developer.android.com/about/dashboards.
Another issue to keep in mind is the device orientation. Do we want to support the landscape mode in our application? If the answer is yes, we have to test our layouts in the landscape orientation. On the toolbar, click on the layout state option to change the mode from portrait to landscape or from landscape to portrait.
In the case that our application supports the landscape mode and the layout does not display as expected in this orientation, we may want to create a variation of the layout. Click on the first icon of the toolbar, that is, the configuration option, and select the option Create Landscape Variation. A new layout will be opened in the editor. This layout has been created in the resources folder, under the directory layout-land and using the same name as the portrait layout: /src/main/res/layout-land/activity_main.xml. Now we can edit the new layout variation perfectly conformed to the landscape mode.
Similarly, we can create a variation of the layout for xlarge screens. Select the option Create layout-xlarge Variation. The new layout will be created in the layout xlarge folder: /src/main/res/layout-xlarge/activity_main.xml. Android divides into small, normal, large, and xlarge the actual screen sizes:
- small: Screens classified in this category are at least 426 dp x 320 dp
- normal: Screens classified in this category are at least 470 dp x 320 dp
- large: Screens classified in this category are at least 640 dp x 480 dp
- xlarge: Screens classified in this category are at least 960 dp x 720 dp
A dp is a density independent pixel, equivalent to one physical pixel on a 160 dpi screen.
The last dashboards published by Google show that most devices have a normal screen size (79.6 percent). If you want to cover a bigger percentage of devices, test your application by also using a small screen (9.5 percent), so the coverage will be 89.1 percent of devices.
To display multiple device configurations at the same time, in the toolbar click on the configuration option and select the option Preview All Screen Sizes, or click on the Preview Representative Sample to open just the most important screen sizes. We can also delete any of the samples by clicking on it using the right mouse button and selecting the Delete option of the menu. Another useful action of this menu is the Save screenshot option, which allows us to take a screenshot of the layout preview.
If we create some layout variations, we can preview all of them selecting the option Preview Layout Versions.
Changing the UI theme
Layouts and widgets are created using the default UI theme of our project. We can change the appearance of the elements of the UI by creating styles. Styles can be grouped to create a theme and a theme can be applied to a whole activity or application. Some themes are provided by default, such as the Holo style. Styles and themes are created as resources under the /src/res/values folder.
Open the main layout using the graphical editor. The selected theme for our layout is indicated in the toolbar: AppTheme. This theme was created for our project and can be found in the styles file (/src/res/values/styles.xml). Open the styles file and notice that this theme is an extension of another theme (Theme.Light).
To custom our theme, edit the styles file. For example, add the next line in the AppTheme definition to change the window background color:
<style name="AppTheme" parent="AppBaseTheme"> <item name="android:windowBackground">#dddddd</item> </style>
Save the file and switch to the layout tab. The background is now light gray. This background color will be applied to all our layouts due to the fact that we configured it in the theme and not just in the layout.
To completely change the layout theme, click on the theme option from the toolbar in the graphical editor. The theme selector dialog is now opened, displaying a list of the available themes.
The themes created in our own project are listed in the Project Themes section. The section Manifest Themes shows the theme configured in the application manifest file (/src/main/AndroidManifest.xml). The All section lists all the available themes.
Summary
In this article, we have seen how to develop and build Android applications with this new IDE.uide. It also shows how to support multiple screens and change their properties using the SDK. The changing of UI themes for the devices is also discussed, along with its properties. The main focus was on the creation of the user interfaces using both the graphical view and the text-based view.
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