我正在尝试将我的应用中的方法转换为异步方法。这是一种在Google Map视图上加载大量自定义标记的方法。我需要使这个异步，以便在标记加载时立即显示视图。
任何人都可以帮我提一下如何将以下方法转换为异步方法吗？我正在努力理解这个概念。谢谢。
private void showpins() throws IOException {
SQLiteDatabase db = mDbHelper.getReadableDatabase();
Cursor mCursor = db.query(TABLE_NAME, null, null, null, null, null, null);
startManagingCursor(mCursor);
while (mCursor.moveToNext()) {
Address = mCursor.getString(4);
Name = mCursor.getString(0);
String noSpaces = Address.replaceAll(" ", "+");
JSONObject geocoded = getLocationInfo(noSpaces);
GeoPoint point = getGeoPoint(geocoded);
List<Overlay> mapOverlays = mapView.getOverlays();
Drawable drawable = this.getResources().getDrawable(R.drawable.pushpin);
CustomizedItemOverlay itemizedOverlay =
new CustomizedItemOverlay(drawable, this);
OverlayItem overlayitem =
new OverlayItem(point, Name, Address);
itemizedOverlay.addOverlay(overlayitem);
mapOverlays.add(itemizedOverlay);
}
}
答案 0 :(得分：0)
我做了类似的事情。但是它有为每个图像创建一个新线程的问题，因此最终崩溃。这对我来说是必要的（有点），但如果你没有从互联网上获取图像，你应该能够做到这一点。这是代码 -
/**
*
* @author Kyle
*/
public class HelloItemizedOverlay extends ItemizedOverlay {
private ArrayList<OverlayItem> mOverlays = new ArrayList<OverlayItem>();
private Context mContext;
public HelloItemizedOverlay(Drawable defaultMarker, Context context) {
super(boundCenterBottom(defaultMarker));
populate();
mContext = context;
}
@Override
public boolean onTouchEvent(MotionEvent event, final MapView mapView) {
//---when user lifts his finger---
if (event.getAction() == MotionEvent.ACTION_UP) {
new Thread(new Runnable() {
public void run() {
ArrayList db = MainActivity.getDB(mContext);
int i=0;
for (Object o : db) {
if(i>40)break;
final ArrayList list = ((ArrayList) o);
final int lon = (int) ((Double.parseDouble("" + list.get(1)) * 1000000.0) + .5);
final int lat = (int) ((Double.parseDouble("" + list.get(2)) * 1000000.0) + .5);
final GeoPoint point = new GeoPoint(lat, lon);
if (isCurrentLocationVisible(mapView, point)) {
Log.i("***", "POINT IS VISIBLE");
if (mOverlays.size() > 40) {
i++;
Log.i("***", i+"");
removeOverlay(0);
}
if (lat != 0) {
Thread t=new Thread(new Runnable() {
public void run() {
final OverlayItem overlayitem = new OverlayItem(point, "" + lat + " " + lon, list.get(0).toString().replace("jpg", "mjpg").replace("image", "video"));
final String url = list.get(0).toString().replace("mjpg", "jpg").replace("video", "image");
Drawable d = MainActivity.getImage(url);
if (d != null) {
d.setBounds(0, 0, 48, 32);
overlayitem.setMarker(d);
addOverlay(overlayitem);
mapView.postInvalidate();
}
}
});
t.setPriority(Thread.MIN_PRIORITY);
t.start();
}
} else {
Log.i("***", "POINT IS OUTSIDE VISIBLE RECT");
}
}
}
}).start();
}
return false;
}
public void addOverlay(OverlayItem overlay) {
mOverlays.add(overlay);
populate();
}
public void removeOverlay(int index) {
try {
mOverlays.remove(index);
} catch (Exception e) {
Log.e("***", e.toString());
}
populate();
}
@Override
protected OverlayItem createItem(int i) {
return mOverlays.get(i);
}
@Override
public int size() {
return mOverlays.size();
}
@Override
protected boolean onTap(int index) {
OverlayItem item = mOverlays.get(index);
return true;
}
}
和主要活动 -
public class MainActivity extends MapActivity {
public static final String mapsApi = "xxxxxxxxxxxxxxxxxx";
public static final String PREFS_NAME = "CamWorldPrefsFile";
ListView myListView = null;
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle icicle) {
super.onCreate(icicle);
setContentView(R.layout.main);
final MapView mapView = (MapView) findViewById(R.id.mapview);
mapView.setBuiltInZoomControls(true);
mapView.setSatellite(false);
List<Overlay> mapOverlays = mapView.getOverlays();
Drawable drawable = this.getResources().getDrawable(R.drawable.cam);
// d.setBounds(0, 0, d.getIntrinsicWidth()-50, d.getIntrinsicHeight());
final HelloItemizedOverlay itemizedoverlay = new HelloItemizedOverlay(drawable, this);
final DataBaseHelper myDbHelper = new DataBaseHelper(this.getApplicationContext());
try {
myDbHelper.createDataBase();
} catch (IOException ioe) {
throw new Error("Unable to create database");
}
new Thread(new Runnable() {
public void run() {
try {
//myDbHelper.close();
myDbHelper.openDataBase();
String query = "SELECT * from database;";
ArrayList stringList = myDbHelper.selectRecordsFromDBList(query, null);
myDbHelper.close();
for (int i = 0; i < stringList.size() - 1; i++) {
final ArrayList list = (ArrayList) stringList.get(i);
try {
if (Double.parseDouble("" + list.get(1)) != 0) {
Log.i("***", list.get(0).toString().replace("mjpg", "jpg").replace("video", "image"));
// Log.i("***", list.get(2) + " : ");
// Log.i("***", list.get(3) + " : ");
final int lon = (int) ((Double.parseDouble("" + list.get(1)) * 1000000.0) + .5);
final int lat = (int) ((Double.parseDouble("" + list.get(2)) * 1000000.0) + .5);
final GeoPoint point = new GeoPoint(lat, lon);
if (lat != 0) {
Thread t = new Thread(new Runnable() {
public void run() {
final OverlayItem overlayitem = new OverlayItem(point, "" + lat + " " + lon, list.get(0).toString().replace("jpg", "mjpg").replace("image", "video"));
final String url = list.get(0).toString().replace("mjpg", "jpg").replace("video", "image");
Drawable d = MainActivity.getImage(url);
if (d != null) {
d.setBounds(0, 0, 48, 32);
overlayitem.setMarker(d);
itemizedoverlay.addOverlay(overlayitem);
}
}
});
t.setPriority(Thread.MIN_PRIORITY);
t.start();
}
// ("http://151cam.uoregon.edu/axis-cgi/jpg/image.cgi?resolution=160x120")
}
} catch (Exception e) {
Log.i("***", e.getMessage());
}
}
// mapView.invalidate();
} catch (SQLException sqle) {
throw sqle;
}
}
}).start();
mapOverlays.add(itemizedoverlay);
答案 1 :(得分：0)
我不确定你发布的方法所调用的所有方法是什么，但是我假设只有对mapOverlays的调用会影响UI，而其他所有方法都会在后台发生。你可以把它变成像这样的AsyncTask（我认为这最适合作为内部类）：
class OverlayLoader extends AsyncTask<Void, CustomizedItemOverlay, Void> {
List<Overlay> mapOverlays;
@Override
protected onPreExecute() {
mapOverlays = mapView.getOverlays();
}
@Override
protected Void doInBackground(Void... params) {
SQLiteDatabase db = mDbHelper.getReadableDatabase();
Cursor mCursor = db.query(TABLE_NAME, null, null, null, null, null, null);
startManagingCursor(mCursor);
while (mCursor.moveToNext()) {
Address = mCursor.getString(4);
Name = mCursor.getString(0);
String noSpaces = Address.replaceAll(" ", "+");
JSONObject geocoded = getLocationInfo(noSpaces);
GeoPoint point = getGeoPoint(geocoded);
Drawable drawable = this.getResources().getDrawable(R.drawable.pushpin);
CustomizedItemOverlay itemizedOverlay =
new CustomizedItemOverlay(drawable, this);
CustomizedItemOverlay overlayitem = new OverlayItem(point, Name, Address);
itemizedOverlay.addOverlay(overlayItem);
publishProgress(overlayitem);
}
}
@Override
protected void onPublishProgress(CustomizedItemOverlay... overlayItem) {
mapOverlays.add(itemizedOverlay);
}
}