ConstraintLayout vs RelativeLayout

When designing user interfaces for Android applications, selecting the appropriate layout is crucial for achieving a responsive and visually appealing user experience. In this topic, we will compare two layouts: ConstraintLayout and RelativeLayout, and discuss their differences, pros, and cons.

RelativeLayout

Just in case you skipped the topic about layouts, let's refresh your knowledge a bit: RelativeLayout allows you to create user interfaces by specifying the relationships between various UI elements in a relative manner. In simpler terms, it lets you position and align widgets relative to each other or the parent layout, using attributes like rules, alignments, and margins.

For simpler layouts, RelativeLayout can be easier to understand and use. You only need to define the relationship between elements, such as "to the right of" or "below", and the layout takes care of the rest. Although RelativeLayout is simple for basic layouts, it can quickly become complex and hard to manage for more intricate designs. This can make your layout XML files harder to read and maintain.

ConstraintLayout

ConstraintLayout is similar to RelativeLayout: just like RelativeLayout, it arranges views based on connections between sibling views and the parent layout. However, it offers greater flexibility compared to RelativeLayout and seamlessly integrates with Android Studio's Layout Editor, making it more user-friendly. ConstraintLayout is backward-compatible up to API level 9.

Constraints serve as a link or alignment to another view, or parent layout. They specify where the view is positioned along the horizontal or vertical axis, and each view should have at least one constraint for each axis. Android Studio will remind you to set a constraint if you accidentally forget to set one with a red exclamation point near the View in the Component Tree or Attributes tab:

ConstraintLayout enables you to create complex and flexible layouts without the need for nested layouts. This reduces the complexity of your layout hierarchy, making your XML layout files easier to manage. However, rendering them "in-head" might be harder when you're reading them without Android Studio itself. By reducing the need for nested layouts, ConstraintLayout might also improve your app's performance.

ConstraintLayout is fully integrated with Android Studio's Layout Editor. This includes support for drag-and-drop and a visual editor for creating constraints, making it easier to design your UI. It also allows you to control the size and position of your views with a high degree of precision. You can specify dimensions as a percentage of the parent layout or create ratios between different views.

To use ConstraintLayout in your project, you need to include the following dependency in your app-level build.gradle file:

implementation "androidx.constraintlayout:constraintlayout:2.2.0-alpha12"

After that, you can open the XML layout file, find the ConstraintLayout in the palette, and drag it onto your design preview. Most likely, though, it will be your default layout, so you won't need to do that.

Let's add other views there so we can experiment with this layout:

When you drop a view into the Layout Editor, it stays where you leave it, even if it has no constraints. You can set a constraint by dragging the blue dots to the sides of other views:

The blue dot means that a constraint is set for this dot, and the white dot is the other way around. You can also see all the constraints of a selected View in the Attributes tab:

In the Constraint widget, you can set a margin for each side that has a constraint:

Now, every View has a margin of 8dp. This is what the result code looks like now:

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <TextView
        android:id="@+id/textView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="8dp"
        android:layout_marginTop="8dp"
        android:text="TextView"
        app:layout_constraintStart_toEndOf="@+id/imageView"
        app:layout_constraintTop_toTopOf="parent" />

    <ImageView
        android:id="@+id/imageView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="8dp"
        android:layout_marginTop="8dp"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        tools:srcCompat="@tools:sample/avatars" />

    <Button
        android:id="@+id/button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="8dp"
        android:layout_marginTop="8dp"
        android:text="Button"
        app:layout_constraintStart_toEndOf="@+id/imageView"
        app:layout_constraintTop_toBottomOf="@+id/textView" />
</androidx.constraintlayout.widget.ConstraintLayout>

The attributes like app:layout_constraintStart_toStartOf="parent" and app:layout_constraintTop_toTopOf="parent" in ConstraintLayout are used to position a view to the parent's edges, helping to create a responsive layout that adapts to different screen sizes and orientations. There are a lot of other attributes that can help you design better layouts. You can find the whole list in the Android Developers documentation.

Comparison

Now that we've covered the basics of RelativeLayout and ConstraintLayout, let's delve into a direct comparison of the two. Both of these layout managers have their unique strengths and weaknesses, and understanding these differences can help you make an informed decision about which to use in your Android application.

Remember that the choice between RelativeLayout and ConstraintLayout isn't necessarily a matter of one being better than the other. What it is about is choosing the right tool for your specific needs. Here’s what you should keep in mind:

• Positioning: RelativeLayout positions views based on their relationships with sibling views and the parent layout. In contrast, ConstraintLayout uses a constraint-based positioning system, where relationships are defined through constraints.
• Complexity: RelativeLayout is simpler and well-suited for basic layouts. On the other hand, ConstraintLayout is highly flexible and is better equipped to handle complex layouts without the need for nested layouts.
• Nesting: with RelativeLayout, you often need to nest multiple layouts within each other to achieve more complex designs. This can lead to performance issues. ConstraintLayout, however, encourages a flat hierarchy, improving efficiency and performance.
• Flexibility: RelativeLayout has limited flexibility when it comes to intricate layouts. ConstraintLayout is more versatile, offering advanced features like chains, guidelines, barriers, and more, which can be used to create complex and flexible layouts.
• Performance: the performance of RelativeLayout can degrade with nested layouts. In contrast, the flat hierarchy encouraged by ConstraintLayout improves performance, as the system only needs to perform a single measure and layout pass.
• Responsive design: RelativeLayout is less suitable for creating responsive layouts that adapt to different screen sizes and orientations. ConstraintLayout is well-suited for this purpose: it allows for a high degree of control over the size and position of views.
• Visual editor support: Both RelativeLayout and ConstraintLayout are supported in Android Studio's visual editor. However, ConstraintLayout's visual editor provides additional functionality for setting up constraints, making it easier to design complex layouts.

Conclusion

Both RelativeLayout and ConstraintLayout have their advantages and disadvantages. ConstraintLayout generally provides more flexibility and efficiency, especially for more complex and responsive layouts. However, RelativeLayout can still be a good choice for simpler layouts, due to its simplicity and ease of use.