Designing XML UIs for Tablet and Foldable Devices

As Android continues to evolve, accommodating diverse screen sizes and form factors is increasingly important. Tablets and foldable devices present unique challenges and opportunities for UI design. Creating XML layouts that adapt seamlessly across these devices requires careful planning, the use of appropriate resource qualifiers, and the adoption of best practices.

Understanding the Challenges

Designing UIs for tablets and foldables involves several key considerations:

• Screen Size and Density: Tablets have larger screens and varying pixel densities compared to phones. Foldables introduce the concept of multiple screens and screen-size changes during folding and unfolding.
• User Interaction: Tablets often require optimized layouts for touch input, and foldables must support seamless transitions between different screen configurations.
• Performance: Complex layouts can impact performance, especially on lower-end devices. Optimizing layouts is essential to maintain a smooth user experience.

Leveraging Resource Qualifiers

Android’s resource qualifier system is essential for providing device-specific layouts, drawables, and values. Common qualifiers for tablets and foldables include:

• -sw<N>dp: Specifies the smallest screen width in dp. Use this to target devices with a minimum screen width.
• -w<N>dp: Specifies the available screen width in dp. Useful for differentiating layouts based on current width.
• -h<N>dp: Specifies the available screen height in dp.
• -large, -xlarge: Generalized screen size buckets, though sw is generally preferred.
• -port, -land: Specifies portrait or landscape orientation.
• -mdpi, -hdpi, -xhdpi, -xxhdpi, -xxxhdpi: Screen density qualifiers, important for providing appropriate image assets.

Implementing Device-Specific Layouts

Let’s walk through a practical example of designing different layouts for phones, tablets, and foldable devices.

Step 1: Create Base Layout (activity_main.xml)

Start with a default layout in res/layout/activity_main.xml. This will serve as the fallback for devices that don’t match any specific qualifiers.

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:padding="16dp"
    tools:context=".MainActivity">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Hello, Phone!"
        android:textSize="24sp"
        android:layout_marginBottom="16dp"/>

    <Button
        android:id="@+id/my_button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Click Me"/>

</LinearLayout>

Step 2: Tablet Layout (activity_main.xml in res/layout-sw600dp)

For tablets with a smallest width of 600dp or more, create a modified layout. This layout could utilize a dual-pane design or larger UI elements.

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="horizontal"
    android:padding="16dp"
    tools:context=".MainActivity">

    <LinearLayout
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_weight="1"
        android:orientation="vertical">

        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Hello, Tablet!"
            android:textSize="32sp"
            android:layout_marginBottom="16dp"/>

        <Button
            android:id="@+id/my_button"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Click Me"/>

    </LinearLayout>

    <FrameLayout
        android:id="@+id/detail_container"
        android:layout_width="0dp"
        android:layout_height="match_parent"
        android:layout_weight="1"
        android:background="#EEE"/>

</LinearLayout>

In this layout, we use a horizontal LinearLayout to create a dual-pane design, with a left pane for controls and a right pane for detailed content.

Step 3: Foldable Layout (activity_main.xml in res/layout-sw720dp or specific foldable SDK qualifiers)

For foldable devices (which typically have even larger screens when unfolded), you can create another layout with appropriate adjustments.

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="horizontal"
    android:padding="24dp"
    tools:context=".MainActivity">

    <LinearLayout
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_weight="1"
        android:orientation="vertical">

        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Hello, Foldable!"
            android:textSize="40sp"
            android:layout_marginBottom="24dp"/>

        <Button
            android:id="@+id/my_button"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Click Me"/>

    </LinearLayout>

    <FrameLayout
        android:id="@+id/detail_container"
        android:layout_width="0dp"
        android:layout_height="match_parent"
        android:layout_weight="2"
        android:background="#DDD"/>

</LinearLayout>

Here, we provide additional layout tweaks such as increasing the weights or using custom views to best use the additional space offered by the unfolded screen. Specific Foldable SDK features might also inform unique adaptations based on device posture.

Dynamic UI Adjustments with Fragments and Activities

Beyond XML layouts, dynamic UI adjustments through Fragments and Activities are crucial for creating a flexible UI.

Example: Loading Fragments Dynamically

In the MainActivity, load different Fragments based on the device configuration:

import androidx.appcompat.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;

public class MainActivity extends AppCompatActivity {

    private static final String TAG = "MainActivity";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        if (getResources().getBoolean(R.bool.isTablet)) {
            // Load tablet-specific fragment
            Log.d(TAG, "Loading TabletFragment");
            getSupportFragmentManager().beginTransaction()
                    .replace(R.id.detail_container, new TabletFragment())
                    .commit();
        } else {
            // Handle phone-specific UI
            Log.d(TAG, "Running on a phone");
        }
    }
}

Create boolean resources to switch logic easily:

• res/values/bools.xml:

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <bool name="isTablet">false</bool>
</resources>

• res/values-sw600dp/bools.xml:

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <bool name="isTablet">true</bool>
</resources>

Best Practices for Designing XML UIs

• Use ConstraintLayout: ConstraintLayout helps create flexible and adaptable layouts that can handle different screen sizes.
• Avoid Hardcoded Values: Use dimensions from dimens.xml to ensure consistent sizing across devices.
• Test on Multiple Devices: Emulate different screen sizes and densities in the Android emulator, and test on real devices when possible.
• Consider Aspect Ratios: Design layouts that adapt well to various aspect ratios, especially for foldable devices.
• Utilize Vector Graphics: Use VectorDrawables for icons and images to ensure they scale properly without loss of quality.
• Handle Configuration Changes: Properly handle configuration changes like orientation changes to prevent the Activity from being recreated unnecessarily.
• Optimize Layout Performance: Minimize the complexity of layouts and use tools like Lint to identify and fix performance issues.
• Design for Continuity: Foldable devices introduce unique continuity challenges when transitioning between folded and unfolded states. Ensure that your UI smoothly adapts to these transitions.

Working with Foldable Devices Specifically

Foldable devices require additional attention due to their unique form factors and state changes. The following points are particularly relevant:

• Display Features: Use the Jetpack WindowManager library to detect foldable device features such as hinges and screen sizes.
• Posture Detection: Monitor device posture (e.g., folded, unfolded, half-folded) and adapt the UI accordingly.
• Multi-Window Support: Ensure your app handles multi-window mode gracefully, allowing users to run your app side-by-side with other apps.
• Avoid Screen Cutouts: Be mindful of screen cutouts (notches) and design layouts that avoid overlapping with these areas.
• Testing on Foldable Emulators/Devices: The Android Emulator supports simulating foldable devices. Test thoroughly on these emulators as well as physical foldable devices to ensure a great user experience.

Here’s an example of detecting foldable features using the WindowManager library:

import androidx.appcompat.app.AppCompatActivity;
import android.os.Bundle;
import androidx.window.WindowManager;
import androidx.window.WindowInfoRepository;
import androidx.lifecycle.LifecycleOwner;
import androidx.lifecycle.Lifecycle;
import androidx.lifecycle.lifecycleScope;
import kotlinx.coroutines.flow.Flow;
import kotlinx.coroutines.flow.collect;
import androidx.window.layout.WindowInfoTracker;
import androidx.window.layout.WindowLayoutInfo;
import android.util.Log;

public class MainActivity extends AppCompatActivity {

    private static final String TAG = "MainActivity";
    private WindowInfoRepository windowInfoRepository;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        windowInfoRepository = WindowInfoTracker.getOrCreate(this).getWindowInfoRepository();

        lifecycleScope.launch {
            windowInfoRepository.windowLayoutInfo.collect {
                windowLayoutInfo ->
                        Log.d(TAG, "WindowLayoutInfo: " + windowLayoutInfo);
                // Update UI based on hinge position, etc.
            }
        }
    }
}

Conclusion

Designing XML UIs for tablets and foldable devices involves a strategic approach using resource qualifiers, dynamic UI adjustments, and a deep understanding of the unique characteristics of these form factors. By following best practices and continuously testing across various devices, you can create adaptable, user-friendly applications that provide an optimal experience, regardless of screen size or device configuration. As foldable devices gain prominence, designing for these devices will become increasingly crucial for delivering a comprehensive Android user experience. Therefore, make designing for tablets and foldables a cornerstone of your Android development strategy.