How to apply easing animation function on view in Android

问题

I want to apply a translate animation on an Android view (button) using a custom interpolator where the easing function is:

public static float easeOut(float t,float b , float c, float d) {
    if ((t/=d) < (1/2.75f)) {
       return c*(7.5625f*t*t) + b;
    } else if (t < (2/2.75f)) {
       return c*(7.5625f*(t-=(1.5f/2.75f))*t + .75f) + b;
    } else if (t < (2.5/2.75)) {
       return c*(7.5625f*(t-=(2.25f/2.75f))*t + .9375f) + b;
    } else {
       return c*(7.5625f*(t-=(2.625f/2.75f))*t + .984375f) + b;
    }
}

I have an example that uses the custom interpolator like this:

The interpolator is:

public class HesitateInterpolator implements Interpolator {
    public HesitateInterpolator() {
    }

    public float getInterpolation(float t) {
        float x = 2.0f * t - 1.0f;
        return 0.5f * (x * x * x + 1.0f);
    }
}

and is used like this:

ScaleAnimation anim = new ScaleAnimation(0.0f, 1.0f, 0.0f, 1.0f);
anim.setInterpolator(new HesitateInterpolator());

My question is: What are these values b, c, d for?

回答1:

FYI: for people who just want an ease interpolator you can just use myAnimator.setInterpolator(new AccelerateDecelerateInterpolator());

回答2:

I made a library which can solve this problem. AndroidEasingFunctions

回答3:

According to Robert Penner's Easing Functions, as stated here:

t: current time, b: begInnIng value, c: change In value, d: duration

If you want to implement your custom Interpolator, you have to make something like this:

(this would be the implementation for the easeInOutQuint)

public class MVAccelerateDecelerateInterpolator implements Interpolator {

    // easeInOutQuint
    public float getInterpolation(float t) {
        float x;
        if (t<0.5f)
        { 
            x = t*2.0f;
            return 0.5f*x*x*x*x*x;
        }
        x = (t-0.5f)*2-1;
        return 0.5f*x*x*x*x*x+1;
    }
}

Edit: to implement the easing function you need some math knowledge, considering that the getInterpolation method gets only the t parameter, from 0.0 to 1.0.

So basically you need to develop a y(t) function, with t from 0 to 1, and with y values from 0 to 1, as shown below:

What you change is the curve to get from 0 to 1 (in the image the green line is the linear one, for example). You need to 'normalize' the easing functions to remain in the (0, 1) x (0, 1) square, as you can see in my easeInOutQuint implementation.

回答4:

1,2,3 go

1. Create a custom cubic bezier curve using this awesome site. And get the control points for the curve. Between 0,0 and 1,1
2. Interpolator customInterpolator = PathInterpolatorCompat.create(cpX1,cpX2,cpY1,cpY2)
3. Add this customInterpolator to any of your animation.

Added a gist. Some more here.

回答5:

Here is another solution, made possible by a recent addition to android's support library: https://gist.github.com/ebabel/8ff41cad01e9ce1dd9ce

and an example in use:

public static void expand(final View v) {
    v.measure(ViewGroup.LayoutParams.MATCH_PARENT, ViewGroup.LayoutParams.WRAP_CONTENT);
    final int targetHeight = v.getMeasuredHeight();

    if ( v.getHeight() != targetHeight ) {
        // Older versions of android (pre API 21) cancel animations for views with a height of 0 so use 1 instead.
        v.getLayoutParams().height = 1;
        v.setVisibility(View.VISIBLE);


        Animation a = new Animation() {
            @Override
            protected void applyTransformation(float interpolatedTime, Transformation t) {
                v.getLayoutParams().height = interpolatedTime == 1
                        ? ViewGroup.LayoutParams.WRAP_CONTENT
                        : (int) (targetHeight * interpolatedTime);
                v.requestLayout();
            }

            @Override
            public boolean willChangeBounds() {
                return true;
            }
        };

        a.setInterpolator(EasingsConstants.easeInOutQuart);
        a.setDuration(computeDurationFromHeight(v));
        v.startAnimation(a);
    } else {
        Log.d("AnimationUtil", "expand Already expanded ");
    }
}

/**
 * 1dp/ms * multiplier
 */
private static int computeDurationFromHeight(View v) {
    return (int) (v.getMeasuredHeight() / v.getContext().getResources().getDisplayMetrics().density) * DURATION_MULTIPLIER;
}

来源：https://stackoverflow.com/questions/22896605/how-to-apply-easing-animation-function-on-view-in-android