Guidelines

Creating Control Panel For Wave Generator using Constraint Layout

Post author:Avjeet
Post published:July 30, 2018
Post category:Android FOSSASIA GSoC Pocket Science Lab

In the blog Creating the onScreen Monitor Using CardView I had created the monitors to view the wave properties in this blog we will create the UI of controlling panel that will be used for that monitors with multiple buttons for both analog and digital waveforms.

Which layout to choose?

In today’s world, there are millions of Android devices present with different screen sizes and densities and the major concern of an Android developer is to make the layout that fits all the devices and this task is really difficult to handle with a linear or relative layout with fixed dimensions.

To create a complex layout with lots of views inside the parent using linear layout we have to make use of the attribute layout_weight for their proper stretching and positioning, but such a complex layout require a lot of nesting of weights and android tries to avoid it by giving a warning :

Nested Weights are bad for performance

This is because layout_weight attribute requires a widget to be measured twice[1]. When a LinearLayout with non-zero weights is nested inside another LinearLayout with non-zero weights, then the number of measurements increases exponentially.

So, to overcome this issue we will make use of special type of layout “Constraint Layout” which was introduced in Google I/O 2016.

Features of Constraint Layout:-

It is similar to Relative Layout as all views are laid out according to their relationship with the sibling, but it is more flexible than Relative Layout.
It helps to flatten the view hierarchy for complex layouts.
This layout is created with the help of powerful tool provided by Android which has a palette on the left-hand side from where we can drag and drop the different widgets like TextView, ImageView, Buttons etc. and on the right-hand side it provides options for positioning, setting margins and other styling option like setting color, change text style etc.
It automatically adjusts the layout according to the screen size and hence doesn’t require the use of layout_weight attribute.

In following steps, I will create the controlling panel for Wave generator which is a complex layout with lots of buttons with the help of constraint layout.

Step 1: Add the dependency of the Constraint Layout in the Project

To use Constraint layout add the following to your build.gradle file and sync the project

dependencies {
    implementation "com.android.support.constraint:constraint-layout:1.1.0"
}

Step 2: Applying Guidelines to the layout

Guidelines[3] are anchors that won’t be displayed in your app, they are like one line of a grid above your layout and can be used to attach or constraint your widgets to it. They are only visible on your blueprint or preview editor. These will help to position and constraint the UI components on the screen easily.

For adding guidelines :

As shown in Figure 1 Right-click anywhere on the layout -> Select helpers -> Select horizontal or vertical guideline according to your need.

Figure 1 shows the horizontal guideline being added to the layout.

And for positioning the guideline we have to set the value of attribute layout_constraintGuide_percent

Let’s say we want the guideline to be at the middle of the screen so we’ll set :

app:layout_constraintGuide_percent=”0.50″

For my layout I have added three guideline :

One horizontal guideline at 50%
Two vertical guidelines at 30% and 65%

Doing this will bifurcate the screen into six square blocks as shown in below figure :

Figure 2 shows the blueprint of constraint layout containing two vertical and one horizontal guidelines with their percentage offset from respective bases

Step 3: Adding the buttons in the blocks

Until now we have created six squares blocks, now we have to put a button view in each of the boxes.

First drag and drop button view from the Palette (shown in Figure 3) on the left side inside the box.

Figure 3 shows the layout editor palette
Then we have to set constraints of this button by clicking on the small circle present on the middle of edges and dragging it onto the side of the block facing it.

Figure 4 shows the button widget getting constrained to sides
Set the layout_width and layout_height attribute of the button to be “0dp”, doing this the button will expand in all the direction occupying all the space with respect to the border it has been constrained with.

Figure 6 shows the button widget expanding to all the available space in the box

Similarly, adding buttons in all the square blocks and providing proper theme color we will have a blueprint and layout as shown in Figure 6.

Figure 6 shows the waveform panel blueprint and actual layout for analog waves with six buttons

Following the same steps until now, I have created the other controlling panel layout having buttons for digital waves as shown in Figure 7

Figure 7 shows other constraint layout for digital waves having seven buttons

Detailing and combining the panels to form Complete UI

After adding both the panels we have created in this layout inside the Wave Generator we have the layout as shown in Figure 8

Figure 8 shows the UI of Wave Generator as shown by a actual Android device in the PSLab app.

As we can see on adding the panels the button created inside the layout shrink so as to adapt to the screen and giving out a beautiful button-like appearance.