Add opportunity to set custom interpolator (close #19)

README.md

@@ -199,6 +199,15 @@ circularProgress.setOnProgressChangeListener(new CircularProgressIndicator.OnPro
 
 ---
 
+#### Setting interpolator
+Default interpolator used for running animation is `AccelerateDecelerateInterpolator`,
+but you can set any other one using setter:
+```java
+circularProgress.setInterpolator(new LinearInterpolator());
+```
+
+---
+
 ### Download using Gradle
 
 Add this in your root `build.gradle` at the end of `repositories` in `allprojects` section:

circularprogressindicator/src/main/java/antonkozyriatskyi/circularprogressindicator/CircularProgressIndicator.java

@@ -25,6 +25,7 @@
 import android.util.TypedValue;
 import android.view.View;
 import android.view.animation.AccelerateDecelerateInterpolator;
+import android.view.animation.Interpolator;
 
 import java.lang.annotation.Retention;
 import java.lang.annotation.RetentionPolicy;
@@ -94,6 +95,9 @@ public class CircularProgressIndicator extends View {
     @Nullable
     private OnProgressChangeListener onProgressChangeListener;
 
+    @NonNull
+    private Interpolator animationInterpolator = new AccelerateDecelerateInterpolator();
+
     public CircularProgressIndicator(Context context) {
         super(context);
         init(context, null);
@@ -384,7 +388,7 @@ public Double evaluate(float fraction, Double startValue, Double endValue) {
         }, oldCurrentProgress, progressValue);
         progressAnimator.setDuration(DEFAULT_ANIMATION_DURATION);
         progressAnimator.setValues(angleProperty);
-        progressAnimator.setInterpolator(new AccelerateDecelerateInterpolator());
+        progressAnimator.setInterpolator(animationInterpolator);
         progressAnimator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
             @Override
             public void onAnimationUpdate(ValueAnimator animation) {
@@ -661,6 +665,15 @@ public boolean isFillBackgroundEnabled() {
         return isFillBackgroundEnabled;
     }
 
+    public void setInterpolator(@NonNull Interpolator interpolator) {
+        animationInterpolator = interpolator;
+    }
+
+    @NonNull
+    public Interpolator getInterpolator() {
+        return animationInterpolator;
+    }
+
     @Retention(RetentionPolicy.SOURCE)
     @IntDef({DIRECTION_CLOCKWISE, DIRECTION_COUNTERCLOCKWISE})
     public @interface Direction {