【正文】 u or, in the case of NooYawk, via key presses: Override public boolean onKeyDown(int keyCode, KeyEvent event) { if (keyCode == ) { ( ! ())。 }else if(keycode== ) { (true)。 } return((keyCode, event))。s mapping allows you to create layers as well, so you can mark up the maps as you need to based on user input and your application39。 ItemizedOverlay simplifies this process. To attach an overlay class to your map, just call getOverlays() on your MapView and add () your Overlay instance to it, as we do here with a custom SitesOverlay: (0, 0, (),())。 We will take a closer look at that marker in the next section. Drawing the ItemizedOverlay As the name suggests, ItemizedOverlay allows you to supply a list of points of interest to be displayed on the mapspecifically, instances of OverlayItem. The overlay handles much of the drawing logic for you. Here are the minimum steps to make this work: 1. Override ItemizedOverlayOverlayItem as your own subclass (in this example, SitesOverlay). 2. In the constructor, build your roster of OverlayItem instances, and call populate() when they are ready for use by the overlay. 3. Implement size() to return the number of items to be handled by the overlay. 4. Override createItem() to return OverlayItem instances given an index. 5. When you instantiate your ItemizedOverlay subclass, provide it with a Drawable that represents the default icon (., a pushpin) to display for each item. The marker from the NooYawk constructor is the Drawable used for step 5. It shows a pushpin. You may also wish to override draw() to do a better job of handling the shadow for your markers. While the map will handle casting a shadow for you, it appears you need to provide a bit of assistance for it to know where the bottom of your icon is, so it can draw the shadow appropriately. For example, here is SitesOverlay: private class SitesOverlay extends ItemizedOverlayOverlayItem { private ListOverlayItem items=new ArrayListOverlayItem()。 public SitesOverlay(Drawable marker){ super(marker)。 (new OverlayItem(getPoint(,), UN, United Nations))。 7 (new OverlayItem (getPoint(,), Carnegie Hall, Where you go with practice, practice, practice))。 populate()。} Override public void draw(Canvas canvas, MapView mapView, boolean shadow) (canvas, mapView, shadow)。} Override protected boolean onTap(int i) { (,(i).getSnippet(), ) .show()。} Override public int size() { return(())。s location. With onTap(), you can do much the same in Android. The onTap() method for ItemizedOverlay receives the index of the OverlayItem that was clicked. It is up to you to do something worthwhile with this event. In the case of SitesOverlay, as shown in the preceding section, onTap() looks like this: Override protected boolean onTap(int i) { (,(i).getSnippet(), ).show()。s list of overlays, and enable and disable the desired features at appropriate times. The at appropriate times notion is for maximizing battery life. There is no sense in updating locations or directions when the activity is paused, so it is remended that you enable these features in onResume() and disable them in onPause(). For example, NooYawk will display a pass rose using MyLocationOverlay. To do this, we first need to create the overlay and add it to the list of overlays: me=new MyLocationOverlay(this, map)。 Then we enable and disable the pass rose as appropriate: Override public void onResume() { ()。} Override public void onPause(){ ()。} The Key to It All If you actually download the source code for the book, pile the NooYawk project, install it in your emulator, and run it, you will probably see a screen with a grid and a couple of pushpins, but no actual maps. That39。s focus on the narrow case of getting NooYawk running in your emulator. Doing this requires the following steps: 1. Visit the API key signup page and review the terms of service. 2. Reread those terms of service and make really sure you want to agree to them. 3. Find the MD5 digest of the certificate used for signing your debugmode applications. 4. On the API key signup page, paste in that MD5 signature and submit the form. 5. On the resulting page, copy the API key and paste it as the value of apiKey in your MapViewusing layout. The trickiest part is finding the MD5 signature of the certificate used for signing your debugmode applications. Actually, much of the p