FoldingTabBar Comes to Android. Thank You, Google!

A sort of UI revolution in Android development has happened recently.  Ready for it?

Google finally added a bottom tab bar as a recommended design pattern for Android development! Hurray! Long live Google!

Obviously, there are no tab bar components by Google in the support libraries yet. So we decided that it’s time to bring our legendary FoldingTabBar to Android – before 2017 arrives.

In case you don’t know, we created FoldingTabBar for iOS about a year ago. FoldingTabBar for iOS quickly became popular, so we’re sure that the same Android Tab Bar will be just as popular.

Before we started building our Android library, we came across this implementation (for Android) of our original iOS design. But honestly, it’s far from perfect. There are lot of issues with code quality and implementation. We don’t recommend putting that piece of code in your app. Open source tab bar solutions weren't of satisying quality either.

What we do recommend is using our very own Yalantis FoldingTabBar library. Here’s how you can use it.

FoldingTabBar for Android

How to use our FoldingTabBar library

It’s very simple. On Android we have the @menu resource type. We can think of FoldingTabBar as a solution that provides folding menu effect. Let’s create our menu file:

<?xml version="1.0" encoding="utf-8"?>
<menu xmlns:android="http://schemas.android.com/apk/res/android">
    <item
        android:id="@+id/ftb_menu_nearby"
        android:icon="@drawable/ic_nearby_icon"
        android:title="Nearby"/>
 
    <item
        android:id="@+id/ftb_menu_new_chat"
        android:icon="@drawable/ic_new_chat_icon"
        android:title="Chat"/>
 
    <item
        android:id="@+id/ftb_menu_profile"
        android:icon="@drawable/ic_profile_icon"
        android:title="Profile"/>
 
    <item
        android:id="@+id/ftb_menu_settings"
        android:icon="@drawable/ic_settings_icon"
        android:title="Settings"/>
 
</menu>

Looks good. This is the menu that you’re using for dialogs, toolbar menus, or the navigation drawer. The coolest thing is that you can easily switch from the navigation drawer to our FoldingTabBar. Or you can use both menus simultaneously on the same screen; not all Android action bars have that flexibility.

 Here’s an example of how you can implement our FoldingTabBar into your layout file:

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
    android:id="@+id/activity_main"
    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"
    android:background="@color/colorAccent"
    tools:context="client.yalantis.com.foldingtabbarandroid.MainActivity">
 
    <android.support.v4.view.ViewPager
        android:id="@+id/viewPager"
        android:layout_width="match_parent"
        android:layout_height="match_parent">
    </android.support.v4.view.ViewPager>
 
    <client.yalantis.com.foldingtabbar.FoldingTabBar
        android:id="@+id/folding_tab_bar"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginBottom="@dimen/activity_horizontal_margin"
        android:layout_centerInParent="true"
        android:layout_alignParentBottom="true"
        app:menu="@menu/menu_tab_bar"/>
</RelativeLayout>

As you can see, we have some custom attributes. The main and required attribute is app:menu – here you can link your menu file to our component.

There are also some additional attributes:

  • app:itemPadding - sets padding for your menu items. Default item padding is 17dp.

  • app:mainImage - here you can link your image resource for the main image.

  • app:selectionColor - our menu supports color selection. You can change the menu’s color here.

Our menu is flexible, so you can use wrap_content or hard-coded sizes. When you’re using wrap_content, the size will equal 70dp.

How to use our FoldingTabBar in Java code

Here we have two interfaces. The first works when your menu item is pressed:

tabBar.setOnFoldingItemClickListener(new FoldingTabBar.OnFoldingItemSelectedListener() {
            @Override
            public boolean onFoldingItemSelected(@NotNull MenuItem item) {
                switch (item.getItemId()) {
                    case R.id.ftb_menu_nearby:
                        mViewPager.setCurrentItem(0);
                        break;
                    case R.id.ftb_menu_new_chat:
                        mViewPager.setCurrentItem(1);
                        break;
                    case R.id.ftb_menu_profile:
                        mViewPager.setCurrentItem(2);
                        break;
                    case R.id.ftb_menu_settings:
                        mViewPager.setCurrentItem(3);
                        break;
                }
                return false;
            }
        });

The second works when a user presses the home button:

tabBar.setOnMainButtonClickListener(new FoldingTabBar.OnMainButtonClickedListener() {
            @Override
            public void onMainButtonClicked() {
               
            }
        });

We created two interfaces instead of one because this corresponds with the Interface Segregation principle (from SOLID).

Technology stack

We chose Kotlin as the language for our library. We already have a few components in Kotlin; we love Kotlin because it’s a powerful language that makes it much more fun to develop apps than Java does. It was a good fit for Android action bar development.

Collections

Here we’re using some functional “magic” of Kotlin collections:

mData = mMenu.visibleItems.map {
            initAndAddMenuItem(it)
        }

Also, note that we’ve used forEach instead of for loops.

Null Safety

This fantastic feature of Kotlin is used everywhere across our library (where needed, of course). Now our code is much cleaner and more understandable.

Lambda functions

We’ve only had this feature in Java since version 8. But Java 8 is not yet ready for Android. In Kotlin we have this feature by default.

rotationAnimator.addUpdateListener {
            valueAnimator ->
            val value = valueAnimator.animatedValue as Float
            mainImageView.rotation = value
        }

Really beautiful, isn’t it?

Apply function

The apply function defines an extension function for all types. When you invoke the apply function, it calls the closure passed as a parameter and then returns the receiver object that the closure ran on. This is an amazing feature!

val scalingAnimator = ValueAnimator.ofInt(mSize, destWidth).apply {
            addUpdateListener(scaleAnimator)
            addListener(rollUpListener)
        }

Animations

We’re using different ValueAnimators and, of course, AnimationSets for playing our animators together. Obviously, we made our own interpolator:

internal class CustomBounceInterpolator(val amplitude: Double = 0.1,
                                        val frequency: Double = 0.8) : Interpolator {
 
    override fun getInterpolation(time: Float): Float {
        return (-1.0 * Math.exp(-time / amplitude) *
                Math.cos(frequency * time) + 1).toFloat()
    }
}

That’s all about the technologies. You can find the OfficialFoldingTabar.Android library and many more in our GitHub repository, and you can check out our designs on Dribbble:

Enjoy! :)

Also check out:

Kotlin vs Java: basic syntax differences

We constantly work on various open-source elements of navigation bar or styling tabs, and focus on providing high-quality open-source libraries for various purposes.

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