Implement playback state management

app/src/main/java/org/schabi/newpipe/views/AnimatedProgressBar.java

@@ -0,0 +1,69 @@
+package org.schabi.newpipe.views;
+
+import android.content.Context;
+import android.support.annotation.Nullable;
+import android.util.AttributeSet;
+import android.view.animation.AccelerateDecelerateInterpolator;
+import android.view.animation.Animation;
+import android.view.animation.Transformation;
+import android.widget.ProgressBar;
+
+public final class AnimatedProgressBar extends ProgressBar {
+
+	@Nullable
+	private ProgressBarAnimation animation = null;
+
+	public AnimatedProgressBar(Context context) {
+		super(context);
+	}
+
+	public AnimatedProgressBar(Context context, AttributeSet attrs) {
+		super(context, attrs);
+	}
+
+	public AnimatedProgressBar(Context context, AttributeSet attrs, int defStyleAttr) {
+		super(context, attrs, defStyleAttr);
+	}
+
+	@Override
+	public synchronized void setProgress(int progress) {
+		cancelAnimation();
+		animation = new ProgressBarAnimation(this, getProgress(), progress);
+		startAnimation(animation);
+	}
+
+	private void cancelAnimation() {
+		if (animation != null) {
+			animation.cancel();
+			animation = null;
+		}
+		clearAnimation();
+	}
+
+	private void setProgressInternal(int progress) {
+		super.setProgress(progress);
+	}
+
+	private static class ProgressBarAnimation extends Animation {
+
+		private final AnimatedProgressBar progressBar;
+		private final float from;
+		private final float to;
+
+		ProgressBarAnimation(AnimatedProgressBar progressBar, float from, float to) {
+			super();
+			this.progressBar = progressBar;
+			this.from = from;
+			this.to = to;
+			setDuration(500);
+			setInterpolator(new AccelerateDecelerateInterpolator());
+		}
+
+		@Override
+		protected void applyTransformation(float interpolatedTime, Transformation t) {
+			super.applyTransformation(interpolatedTime, t);
+			float value = from + (to - from) * interpolatedTime;
+			progressBar.setProgressInternal((int) value);
+		}
+	}
+}