Implement approximate state restoration for PhotoView; fixes #20

app/src/main/java/be/digitalia/fosdem/widgets/SaveStatePhotoView.java

@@ -0,0 +1,107 @@
+package be.digitalia.fosdem.widgets;
+
+import android.content.Context;
+import android.graphics.RectF;
+import android.os.Parcel;
+import android.os.Parcelable;
+import android.support.v4.os.ParcelableCompat;
+import android.support.v4.os.ParcelableCompatCreatorCallbacks;
+import android.util.AttributeSet;
+import android.view.ViewTreeObserver;
+
+import uk.co.senab.photoview.PhotoView;
+
+/**
+ * PhotoView which saves and restores the current scale and approximate position.
+ */
+public class SaveStatePhotoView extends PhotoView {
+
+	public SaveStatePhotoView(Context context) {
+		super(context);
+	}
+
+	public SaveStatePhotoView(Context context, AttributeSet attr) {
+		super(context, attr);
+	}
+
+	public SaveStatePhotoView(Context context, AttributeSet attr, int defStyle) {
+		super(context, attr, defStyle);
+	}
+
+	@Override
+	protected Parcelable onSaveInstanceState() {
+		Parcelable superState = super.onSaveInstanceState();
+		SavedState ss = new SavedState(superState);
+		ss.scale = getScale();
+		final RectF rect = getDisplayRect();
+		final float overflowWidth = rect.width() - getWidth();
+		if (overflowWidth > 0f) {
+			ss.pivotX = -rect.left / overflowWidth;
+		}
+		final float overflowHeight = rect.height() - getHeight();
+		if (overflowHeight > 0f) {
+			ss.pivotY = -rect.top / overflowHeight;
+		}
+		return ss;
+	}
+
+	@Override
+	protected void onRestoreInstanceState(Parcelable state) {
+		if (!(state instanceof SavedState)) {
+			super.onRestoreInstanceState(state);
+			return;
+		}
+
+		final SavedState ss = (SavedState) state;
+		super.onRestoreInstanceState(ss.getSuperState());
+
+		getViewTreeObserver().addOnGlobalLayoutListener(new ViewTreeObserver.OnGlobalLayoutListener() {
+			@SuppressWarnings("deprecation")
+			@Override
+			public void onGlobalLayout() {
+				float scale = Math.max(ss.scale, getMinimumScale());
+				scale = Math.min(scale, getMaximumScale());
+				setScale(scale, getWidth() * ss.pivotX, getHeight() * ss.pivotY, false);
+				getViewTreeObserver().removeGlobalOnLayoutListener(this);
+			}
+		});
+	}
+
+	public static class SavedState extends BaseSavedState {
+		float scale = 1f;
+		float pivotX = 0.5f;
+		float pivotY = 0.5f;
+
+		public SavedState(Parcelable superState) {
+			super(superState);
+		}
+
+		@Override
+		public void writeToParcel(Parcel out, int flags) {
+			super.writeToParcel(out, flags);
+			out.writeFloat(scale);
+			out.writeFloat(pivotX);
+			out.writeFloat(pivotY);
+		}
+
+		public static final Parcelable.Creator<SavedState> CREATOR
+				= ParcelableCompat.newCreator(new ParcelableCompatCreatorCallbacks<SavedState>() {
+			@Override
+			public SavedState createFromParcel(Parcel in, ClassLoader loader) {
+				return new SavedState(in);
+			}
+
+			@Override
+			public SavedState[] newArray(int size) {
+				return new SavedState[size];
+			}
+		});
+
+		SavedState(Parcel in) {
+			super(in);
+			scale = in.readFloat();
+			pivotX = in.readFloat();
+			pivotY = in.readFloat();
+		}
+	}
+}

app/src/main/res/layout/fragment_map.xml

@@ -1,5 +1,6 @@
 <?xml version="1.0" encoding="utf-8"?>
-<uk.co.senab.photoview.PhotoView xmlns:android="http://schemas.android.com/apk/res/android"
+<be.digitalia.fosdem.widgets.SaveStatePhotoView
+    xmlns:android="http://schemas.android.com/apk/res/android"
     android:id="@+id/map"
     android:layout_width="match_parent"
     android:layout_height="match_parent"