Develop Reference

Add a layer or a background on a mapView

I have a particular need with a mapView and i can't find any good solution.
I have a Mapview with some markers displayed on it, and it works perfectly.
My need is that i want to put a kind of layer/background on the screen, in order to "mask" the map, but i always want to see the markers, and keep all the mapview functionnalities (zoom, move, etc.)
Is there any solution available to do it?
I hope you understand my need.
Many thanks in advance.

Create an overlay that mask (cover) the part of the map that you want to cover. In the onDraw() of this oevrlay just draw something that achive your mask requirements (areas, colors and opacity).
To ensure that markers are always visible, you need to add the overlay with markers after you add the overlay that mask map to the mapView.getOverlays.add().
Enjoy it.

Custom Overlay MKMapOverlay iOS port of Android method

I have an android app I have written, that basically has a custom overlay, in this overlay I have overwritten the DRAW method to draw something on a canvas and at the end of my DRAW override, I call the super DRAW passing in the canvas I have painted.. the result is, every time the map is modified in anyway my custom overlay is redrawn as expected.
Now, I am trying to accomplish the same thing on iPhone and am getting a little confused.
Basically I need something drawn in the top right corner of the map every time a redraw occurs of the map. The drawin will change change with every update as well so can't simply be put a view over the map and pass touches through etc.
So, I guess the question is, what is the euivalent of the DRAW method in iOS.. how would I roughly accomplish this same thing? There are MKOverlayView in the API, but there seem to be some significant differences.. So, how do I put something say at 10x10 over the map, whos size is variable and make sure every time the map is moved, scaled or otherwised interacted with this object is redrawn at location 10x10 on the screen.

The docs for MKMapView state that you should not subclass MKMapView, so you can't / shouldn't override the drawRect method. You could add a UIView, though, and override drawRect to do your custom drawing.

Adding variable-size labels on top of MapView

I need to add 'balloon'- like markers to my map view. The difficult thing here - these markers include a variable-length text labels so these balloons have variable sizes. Actually this is exactly what implemented in native google-maps application to show labels.
Any idea what is optimal way to do this?

You need to implement custom overlay. This article will be a good start.

You are probably already using itemized overlays. Your OverlayItem class has a method that returns a Drawable; you can create your own Drawable class that your OverlayItem will return. As for the variable size, you could handle that two ways: either your Drawable could determine its own size (using Paint.measureText() ), or, possibly, you could create a View class to take advantage of a View's ability to figure its own layout, and have your Drawable's draw() method delegate to the View's draw() method. Someone who understands Views better than I do can probably improve on that suggestion.

draw is being constantly called in my android map overlay

I'm trying to draw a route onto my MapView.
I've extended Overlay and implemented the draw() method.
The route is displayed properly, although while debugging,
I added a breakpoint on draw(), and noticed it is being called constantly.
I only want it to be re-drawn if someone moves the map or zooms (the draw take into account these changes when drawing the route)
What can cause this ?

There are two draw methods that can be overridden.
void draw(android.graphics.Canvas canvas, MapView mapView, boolean shadow)
Desc: Draw the overlay over the map.
boolean draw(android.graphics.Canvas canvas, MapView mapView, boolean shadow, long when)
Desc: Draw call for animated overlays.
I originally overrided the second one.
After changing to the first method, it worked out.

i think the draw method is called repeatedly because the of the background being redrawn constantly. try setting the "MapView.ReticleDrawMode" to DRAW_RETICLE_UNDER. This basically tells the mapView to draw the reticle under the overlays. So overlay's draw method will not be called when the background is recalled. this fixed the issue for me.
for more info, look here: MapView Api

I got tripped up when I didn't realize that the draw method get's called not only any markers that you draw, BUT also the shadow of those markers. So as an example, if you have two markers and you have shadows set to true (which is the default setting), then you'll have the draw method being called 4 times (once for each marker, once for each shadow of the markers)!

After further review, the Overlay draw() does actually work as described in the documentation. One draw for shadow = true, and one for shadow = false.
The interesting thing is that the specific overlay draw() method responds as advertized for each element drawn in the MapView. For example, in my case, it seems to respond for each the google map, the Google logo drawn on the map, and then the particular overlay I have drawn myself. Obviously twice for each (shadow true|false).
This is probably the intended way to render the maps. I haven't found or spent enough time researching for this information.
Also, in my own case, I have a transparent panel rendered over my map with CheckBox(s) and TextView widgets. The TextView forces the draw() method to run non-stop since the textview is always listening for input and hence triggering the redrawn of the overlay.

In my app, I have an indefinite progress bar (e.g. spinning circle) show when I'm loading network data for the map. When the network data is finished loading, I was setting the progress bar's visibility to invisible. However, this caused the map to continuously redraw as it seems that any animation (I'm guessing) which takes place over the map will cause the map itself to redraw. Simple solution to this is to set the visibility to gone instead. E.g. change this:
ProgressBar loadingIcon = (ProgressBar) findViewById(R.id.loadingIcon);
...
//Network data now finished loading...
loadingIcon.setVisibility(View.INVISIBLE);
to this:
loadingIcon.setVisibility(View.GONE);
which removes it entirely from the map, no longer animates over it and therefore does not cause draw() to be called a indefinitely.

For me it looks like a strange bug - sometimes the draw method is called continously, sometimes not.
see here.

I know this is an old problem, but I just now encountered it. This is a "for what it's worth" post.
The draw loop turned out to be a coding error on my part. According to the doc, if the draw routine returns true, it is asking for an immediate update. If false is returned, only two passes are made for each overlay; one for shadow true and one for shadow false. I was returning true which resulted in a constant update. After I changed to returning false, only two passes per overlay occurred. No loop.

You can simply add this to your ItemizedOverlay class:
#Override public void draw( Canvas c, MapView m, boolean shadow ) { super.draw( c, m, false );}
This will remove the shadow from your mapview overlay.

Not understanding drawAt() method for com.google.android.maps.Overlay

Trying to make an google maps overlay in an android program. Inside of my overlay's draw method, I have two ways of adding a pin. One of them works, and one does not. Unfortunately, the one that does not work is also the only one that has the ability to add a shadow! Any help?
#Override
public void draw(android.graphics.Canvas canvas, MapView mapView,
boolean shadow) {
Point po = mapView.getProjection().toPixels(mapView.getMapCenter(),
null);
// This does _not_ work, but I would really like it to!
drawAt(canvas, mapView.getResources().getDrawable(R.drawable.map_marker_v),
po.x, po.y, false);
// This does work, but only does half the job
canvas.drawBitmap(BitmapFactory.decodeResource(mapView.getResources(),
R.drawable.map_marker_v), po.x, po.y, null);
}
Edit: fixed type

I think your problem may simply be that you haven't set the bounds on the drawable in drawAt(). You can either manually set the bounds using Drawable.setBounds(), or you can use ItemizedOverlay's convenience methods boundCenter() or boundCenterBottom().
I believe the reason the second method works is because with a decoded Bitmap you don't have to specify the bounds of the Drawable.

At first sight, nothing stands out to me as to what could be causing your pin to not draw. But, I might have found a temporarily solution.
Looking on google lead me to this post where an user posts their version of an Overlay with the ability to add an icon along with a shadow. It might be what your looking for.
Hope this helps.