Awesome

GravityBehavior

A CoordinatorLayout.Behavior which aligns a View according to gravity.

Installation

To use the GravityBehavior just add this dependency to your build.gradle:

compile 'com.github.wrdlbrnft:gravity-behavior:0.1.0.4'

If you are using maven you can add it like this:

<dependency>
  <groupId>com.github.wrdlbrnft</groupId>
  <artifactId>gravity-behavior</artifactId>
  <version>0.1.0.4</version>
</dependency>

How to use it

You can add the Behavior to any View which is a direct child of a CoordinatorLayout. The library provides a string resource called gravity_behavior to simplify this:

<?xml version="1.0" encoding="utf-8"?>
<android.support.design.widget.CoordinatorLayout
    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">

    <TextView
        android:id="@+id/text"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center"
        android:text="@string/some_text"
        app:layout_behavior="@string/gravity_behavior"/>

</android.support.design.widget.CoordinatorLayout>

After that you can get the GravityBehavior instance for a View by calling GravityBehavior.of():

private GravityBehavior mGravityBehavior;

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

    final View view = findViewById(R.id.text);
    mGravityBehavior = GravityBehavior.of(view);
}

With the GravityBehavior instance you can start and stop rotating the View by calling start() and stop(). To conserve battery and avoid memory leaks you should always stop the behavior when the View is not visible. In most cases it makes sense to simply call start() in onResume() and stop() in onPause():

@Override
protected void onResume() {
    super.onResume();
    mGravityBehavior.start();
}

@Override
protected void onPause() {
    super.onPause();
    mGravityBehavior.stop();
}

And that's everything you have to do to get GravityBehavior to work.

Additional Options

Smoothing Factor

GravityBehavior internally smooths out sensor values with a very simple filter. The amount of smoothing can be controlled with a smoothing factor which can be modified with a setter:

mGravityBehavior.setSmoothingFactor(8.0f);

The default smoothing factor is 4.0f (there is also a public constant in the GravityBehavior for that). Increasing the smoothing factor will make the rotation of the View smoother, but it will also react more slowly to changes in the orientation of the device. 4.0f should be the optimal compromise of smoothness and reaction speed for most devices, but you can play around with it a little if you want.

Base Rotation

GravityBehavior can apply a base rotation to the View. The View will always be rotated by the base rotation in addition to the rotation applied by GravityBehavior. The GravityBehavior exposes a setter for the base rotation:

mGravityBehavior.setBaseRotation(90.0f);

And GravityBehavior also exposes a Property for use in an Animator so you can easily animate the base rotation value:

final Animator animator = ObjectAnimator.ofFloat(view, GravityBehavior.BASE_ROTATION, 0.0f, 90.0f);
animator.start();