Some work for properly animating our single (value-changing) entry

app/src/main/java/nodomain/freeyourgadget/gadgetbridge/activities/charts/SingleEntryValueAnimator.java

@@ -0,0 +1,48 @@
+package nodomain.freeyourgadget.gadgetbridge.activities.charts;
+
+import android.animation.Animator;
+import android.animation.ObjectAnimator;
+import android.animation.ValueAnimator;
+
+import com.github.mikephil.charting.animation.ChartAnimator;
+import com.github.mikephil.charting.data.Entry;
+
+public class SingleEntryValueAnimator extends ChartAnimator {
+    private final Entry entry;
+    private final ValueAnimator.AnimatorUpdateListener listener;
+    private float previousValue;
+
+    public SingleEntryValueAnimator(Entry singleEntry, ValueAnimator.AnimatorUpdateListener listener) {
+        super(listener);
+        this.listener = listener;
+        entry = singleEntry;
+    }
+
+    public void setEntryYValue(float value) {
+        this.previousValue = entry.getVal();
+        entry.setVal(value);
+    }
+
+    @Override
+    public void animateY(int durationMillis) {
+        // we start with the previous value and animate the change to the
+        // next value.
+        // as our animation values are not used as absolute values, but as factors,
+        // we have to calculate the proper factors in advance. The entry already has
+        // the new value, so we create a factor to calculate the old value from the
+        // new value.
+
+        float startAnim;
+        float endAnim = 1f;
+        if (entry.getVal() == 0f) {
+            startAnim = 0f;
+        } else {
+            startAnim = previousValue / entry.getVal();
+        }
+
+        ObjectAnimator animatorY = ObjectAnimator.ofFloat(this, "phaseY", startAnim, endAnim);
+        animatorY.setDuration(durationMillis);
+        animatorY.addUpdateListener(listener);
+        animatorY.start();
+    }
+}