HorizontalChangeHandler sliding from/to the left

“I’m a very lazy programmer. One of my forms of laziness is that I never remember things about the code I write. Indeed, I deliberately try not to remember anything I can look up, because I’m afraid my brain will get full. I make a point of trying to put everything I should remember into the code so I don’t have to remember it.”

— Martin Fowler (from his Refactoring book, p. 56)

Another form of laziness that we, programmers, have is to not rewrite anything that is already written by other programmers.

But how would we know if the code we want to write is already written by other programmers?

By googling for it, of course!

That might be the reason why you are in this page! — You are using Conductor in your Android app, and you want an AnimatorChangeHandler which slides your screens from/to the left… and you are lazy (or, as in my case, do not know how to do it )… so you googled for it.

I tried it… and found none.

So I created one myself — I just copied the code for the HorizontalChangeHandler provided by Conductor and then made some changes to it.

I hope this helps my fellow lazy programmers!

Here it is:

import android.animation.Animator;
import android.animation.AnimatorSet;
import android.animation.ObjectAnimator;
import android.support.annotation.NonNull;
import android.support.annotation.Nullable;
import android.view.View;
import android.view.ViewGroup;

import com.bluelinelabs.conductor.ControllerChangeHandler;
import com.bluelinelabs.conductor.changehandler.AnimatorChangeHandler;

public class LeftHorizontalChangeHandler extends AnimatorChangeHandler {

    public LeftHorizontalChangeHandler() { }

    public LeftHorizontalChangeHandler(boolean removesFromViewOnPush) {
        super(removesFromViewOnPush);
    }

    public LeftHorizontalChangeHandler(long duration) {
        super(duration);
    }

    public LeftHorizontalChangeHandler(long duration, boolean removesFromViewOnPush) {
        super(duration, removesFromViewOnPush);
    }

    @Override @NonNull
    protected Animator getAnimator(@NonNull ViewGroup container, @Nullable View from, @Nullable View to, boolean isPush, boolean toAddedToContainer) {
        AnimatorSet animatorSet = new AnimatorSet();

        if (isPush) {
            if (from != null) {
                animatorSet.play(ObjectAnimator.ofFloat(from, View.TRANSLATION_X, from.getWidth()));
            }
            if (to != null) {
                animatorSet.play(ObjectAnimator.ofFloat(to, View.TRANSLATION_X, -to.getWidth(), 0));
            }
        } else {
            if (from != null) {
                animatorSet.play(ObjectAnimator.ofFloat(from, View.TRANSLATION_X, -from.getWidth()));
            }
            if (to != null) {
                // Allow this to have a nice transition when coming off an aborted push animation
                float fromLeft = from != null ? from.getTranslationX() : 0;
                animatorSet.play(ObjectAnimator.ofFloat(to, View.TRANSLATION_X, fromLeft + to.getWidth(), 0));
            }
        }

        return animatorSet;
    }

    @Override
    protected void resetFromView(@NonNull View from) {
        from.setTranslationX(0);
    }

    @Override @NonNull
    public ControllerChangeHandler copy() {
        return new LeftHorizontalChangeHandler(getAnimationDuration(), removesFromViewOnPush());
    }
}

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