Android – ConstraintLayout percentage using dimens

Introduction

ConstraintLayout is a powerful layout system in Android that allows developers to create complex and flexible UI designs. One of its key features is the ability to position and size views using constraints, which can be defined as percentages of the parent view. This provides a more flexible and maintainable approach compared to using fixed pixel values.

This article explores how to utilize the `dimens.xml` file to define percentage-based constraints within ConstraintLayout.

Using Dimens for Percentages

The `dimens.xml` file is a standard resource file in Android where you define dimension values. We can leverage this file to store percentage values, making our code more readable and adaptable.

Defining Percentage Values in `dimens.xml`

Open the `dimens.xml` file (typically found in the `values` folder) and define your percentage values as follows:

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <dimen name="view_width_percentage">50%</dimen>
    <dimen name="view_height_percentage">75%</dimen>
</resources>

Applying Percentage Constraints in Layout

In your layout XML file (e.g., `activity_main.xml`), reference these defined percentage values using the `app:layout_constraintDimensionRatio` attribute:

<androidx.constraintlayout.widget.ConstraintLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <Button
        android:id="@+id/myButton"
        android:layout_width="0dp"
        android:layout_height="0dp"
        android:text="My Button"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintDimensionRatio="H, @dimen/view_width_percentage">
    </Button>

</androidx.constraintlayout.widget.ConstraintLayout>

In this example:

• We define a button (`myButton`).
• `app:layout_constraintDimensionRatio` sets the aspect ratio of the button.
• `H` specifies that the ratio is horizontal (width to height).
• `@dimen/view_width_percentage` references the previously defined dimension in `dimens.xml`, making the button’s width 50% of its parent.

Benefits of Using Dimens

Code Readability and Maintainability

By storing percentage values in `dimens.xml`, our layout code becomes more concise and understandable. Instead of hardcoded percentages, we use meaningful names that clearly communicate the intended proportions. This improves readability and reduces the need for comments.

Flexibility and Adaptability

When using percentage-based constraints, we can easily adapt our UI to different screen sizes and resolutions. The layout will automatically scale according to the defined percentages, ensuring a consistent look across various devices. This eliminates the need for manual adjustments for different screen densities.

Comparison with Hardcoded Percentages

| Feature | Dimens | Hardcoded Percentages |
|—|—|—|
| Readability | More readable and maintainable | Less readable, especially for complex layouts |
| Flexibility | Easy to adjust for different screen sizes | Requires manual adjustments for different screen sizes |
| Reusability | Can be reused across different views and layouts | Less reusable, requiring duplication of code |

Conclusion

Utilizing `dimens.xml` to define percentage-based constraints within ConstraintLayout offers significant advantages in terms of code readability, flexibility, and maintainability. It promotes a more organized and adaptable development approach for Android UI design. By adopting this practice, developers can create visually appealing and scalable user interfaces with ease.