21. An Android Studio Layout Editor ConstraintLayout Tutorial

By far the easiest and most productive way to design a user interface for an Android application is to make use of the Android Studio Layout Editor tool. The goal of this chapter is to provide an overview of how to create a ConstraintLayout-based user interface using this approach. The exercise included in this chapter will also be used as an opportunity to outline the creation of an activity starting with a “bare-bones” Android Studio project.

Having covered the use of the Android Studio Layout Editor, the chapter will also introduce the Layout Inspector tool.

21.1 An Android Studio Layout Editor Tool Example

The first step in this phase of the example is to create a new Android Studio project. Begin, therefore, by launching Android Studio and closing any previously opened projects by selecting the File -> Close Project menu option.

Select the Create New Project quick start option from the welcome screen. In previous examples, we have requested that Android Studio create a template activity for the project. We will, however, be using this tutorial to learn how to create an entirely new activity and corresponding layout resource file manually, so make sure that the No Activity option is selected before clicking on the Next button

Enter LayoutSample into the Name field and specify com.ebookfrenzy.layoutsample as the package name. Before clicking on the Finish button, change the Minimum API level setting to API 26: Android 8.0 (Oreo) and the Language menu to Java.

21.2 Creating a New Activity

Once the project creation process is complete, the Android Studio main window should appear. The first step in the project is to create a new activity. This will be a valuable learning exercise since there are many instances in the course of developing Android applications where new activities need to be created from the ground up.

Begin by displaying the Project tool window if it is not already visible using the Alt-1/Cmd-1 keyboard shortcut. Once displayed, unfold the hierarchy by clicking on the right facing arrows next to the entries in the Project window. The objective here is to gain access to the app -> java -> com.ebookfrenzy.layoutsample folder in the project hierarchy. Once the package name is visible, right-click on it and select the New -> Activity -> Empty Activity menu option as illustrated in Figure 21-1. Alternatively, select the New -> Activity -> Gallery... option to browse the available templates and make a selection...

21.3 Preparing the Layout Editor Environment

Locate and double-click on the activity_main.xml layout file located in the app -> res -> layout folder to load it into the Layout Editor tool. Since the purpose of this tutorial is to gain experience with the use of constraints, turn off the Autoconnect feature using the button located in the Layout Editor toolbar. Once disabled, the button will appear with a line through it as is the case in Figure 21-2:

Figure 21-2

If the default margin value to the right of the Autoconnect button is not set to 8dp, click on it and select 8dp from the resulting panel.

The user interface design will also make use of the ImageView object to display an image. Before proceeding, this image should be added to the project ready for use later in the chapter. This file is named galaxys6.png and can be found in the project_icons folder of the sample code download available from the following URL:

https://www.ebookfrenzy.com/retail/androidstudio41...

21.4 Adding the Widgets to the User Interface

From within the Common palette category, drag an ImageView object into the center of the display view. Note that horizontal and vertical dashed lines appear indicating the center axes of the display. When centered, release the mouse button to drop the view into position. Once placed within the layout, the Resources dialog will appear seeking the image to be displayed within the view. In the search bar located at the top of the dialog, enter “galaxy” to locate the galaxys6.png resource as illustrated in Figure 21-5.

Figure 21-5

Select the image and click on OK to assign it to the ImageView object. If necessary, adjust the size of the ImageView using the resize handles and reposition it in the center of the layout. At this point the layout should match Figure 21-6:

Figure 21-6

Click and drag a TextView object from the Common section of the palette and position it so that it appears above the ImageView as...

21.5 Adding the Constraints

Constraints are the key to creating layouts that can adapt to device orientation changes and different screen sizes. Begin by rotating the layout back to portrait orientation and selecting the TextView widget located above the ImageView. With the widget selected, establish constraints from the left, right and top sides of the TextView to the corresponding sides of the parent ConstraintLayout as shown in Figure 21-10:

Figure 21-10

With the TextView widget constrained, select the ImageView instance and establish opposing constraints on the left and right-hand sides with each connected to the corresponding sides of the parent layout. Next, establish a constraint connection from the top of the ImageView to the bottom of the TextView and from the bottom of the ImageView to the top of the center Button widget. If necessary, click and drag the ImageView so that it is still positioned in the vertical center of the layout.

With the ImageView still selected...

21.6 Testing the Layout

With the constraints added to the layout, rotate the screen into landscape orientation and verify that the layout adapts to accommodate the new screen dimensions.

While the Layout Editor tool provides a useful visual environment in which to design user interface layouts, when it comes to testing there is no substitute for testing the running app. Launch the app on a physical Android device or emulator session and verify that the user interface reflects the layout created in the Layout Editor. Figure 21-14, for example, shows the running app in landscape orientation:

Figure 21-14

The user interface design is now complete. Designing a more complex user interface layout is a continuation of the steps outlined above. Simply drag and drop views onto the display, position, constrain and set properties as needed.

21.7 Using the Layout Inspector

The hierarchy of components that make up a user interface layout may be viewed at any time using the Layout Inspector tool. In order to access this information the app must be running on a device or emulator. Once the app is running, select the Tools -> Layout Inspector menu option followed by the process to be inspected using the menu marked A in Figure 21-15 below).

Once the inspector loads, the left most panel (B) shows the hierarchy of components that make up the user interface layout. The center panel (C) shows a visual representation of the layout design. Clicking on a widget in the visual layout will cause that item to highlight in the hierarchy list making it easy to find where a visual component is situated relative to the overall layout hierarchy.

Finally, the rightmost panel (marked D in Figure 21-15) contains all of the property settings for the currently selected component, allowing for in-depth analysis of the component’...

21.8 Summary

The Layout Editor tool in Android Studio has been tightly integrated with the ConstraintLayout class. This chapter has worked through the creation of an example user interface intended to outline the ways in which a ConstraintLayout-based user interface can be implemented using the Layout Editor tool in terms of adding widgets and setting constraints. This chapter also introduced the Live Layout Inspector tool which is useful for analyzing the structural composition of a user interface layout.