I have a LinearLayout in my Android app and I would like to make it scrollable in all directions. I simply implemented this with a HorizontalScrollView and ScrollView under which I placed my layout.
This works great, but I would like to implement pinch-zoom as well. So I was inspired by this question: Android - zoom in/out RelativeLayout with spread/pinch
and I came up with the following layout:
<com.example.ZoomableScrollView
android:layout_width="wrap_content"
android:layout_height="match_parent"
android:layout_weight="0.2"
android:scrollbars="none"
android:background="@android:color/black">
<HorizontalScrollView
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:scrollbars="none">
<LinearLayout
android:id="@+id/sheet_layout"
android:layout_width="wrap_content"
android:layout_height="match_parent"
android:orientation="vertical"
tools:context=".MainActivity">
</LinearLayout>
</HorizontalScrollView>
</com.example.ZoomableScrollView>
The children of the inner LinearLayout are dynamically added (they are simple TextViews inside horizontal LinearLayouts to make a simple table).
The ZoomableScrollView is quite simple and looks like this:
public class ZoomableScrollView extends ScrollView {
float mScaleFactor = 1.f;
private final ScaleGestureDetector mScaleDetector;
static final float MIN_SCALE = 1f;
static final float MAX_SCALE = 4f;
public ZoomableScrollView(Context context) {
this(context, null, 0);
}
public ZoomableScrollView(Context context, AttributeSet attrs) {
this(context, attrs, 0);
}
public ZoomableScrollView(Context context, AttributeSet attrs,
int defStyle) {
super(context, attrs, defStyle);
mScaleDetector = new ScaleGestureDetector(context, new OnScaleListener());
}
@Override
public boolean onTouchEvent(MotionEvent event) {
Log.w("DEBUG", "On touch event");
boolean retVal = mScaleDetector.onTouchEvent(event);
return super.onTouchEvent(event) || retVal;
}
@Override
protected void dispatchDraw(Canvas canvas) {
Log.w("DEBUG", String.format("Scaling with scale factor %f", mScaleFactor));
canvas.save(Canvas.MATRIX_SAVE_FLAG);
canvas.scale(mScaleFactor, mScaleFactor);
super.dispatchDraw(canvas);
canvas.restore();
}
@Override
public void onDraw(Canvas canvas) {
super.onDraw(canvas);
}
private class OnScaleListener extends ScaleGestureDetector.SimpleOnScaleGestureListener
{
@Override
public boolean onScale(ScaleGestureDetector detector)
{
mScaleFactor *= detector.getScaleFactor();
// Don't let the object get too small or too large.
mScaleFactor = Math.max(MIN_SCALE, Math.min(mScaleFactor, MAX_SCALE));
Log.w("DEBUG", "OnScale: scale factor: " + mScaleFactor);
invalidate();
return true;
}
}
}
I have 2 issues with this:
- The zooming is not very smooth, sometimes the View will scroll when it should zoom. That's not such a big deal atm.
- When zooming, the
LinearLayoutbecomes smaller and you can't scroll everywhere anymore. I think I understand why this is the case, but I don't know how to change that and I'm thinking that I went into the wrong direction here.
I don't mind changing the layout completely. In the end, I would like to have it behave a bit like a browser, where you can zoom and scroll everywhere (not as complex though). Is there a simple solution for this ?
