我在将ArrayList课程中创建的OverlayItems CustomPinpoint链接到Listview时遇到问题。基本上我正试图在一个小清单中显示我在地图上添加的标记。但是使用下面的代码，我收到NullPointerException错误。我理解为什么（我认为它是因为我创建了两个不相互引用的“自定义”单独实例），但我不明白我是如何解决它的......
提前谢谢。
package com.lars.pinpoint;
import java.io.IOException;
import java.util.List;
import java.util.Locale;
import com.google.android.maps.GeoPoint;
import com.google.android.maps.MapActivity;
import com.google.android.maps.MapController;
import com.google.android.maps.MapView;
import com.google.android.maps.MyLocationOverlay;
import com.google.android.maps.Overlay;
import com.google.android.maps.OverlayItem;
import com.lars.pinpoint.R;
import android.app.AlertDialog;
import android.content.DialogInterface;
import android.graphics.drawable.Drawable;
import android.location.Address;
import android.location.Geocoder;
import android.os.Bundle;
import android.view.MotionEvent;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemClickListener;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import android.widget.TabHost;
import android.widget.TextView;
import android.widget.Toast;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.MenuItem;
import android.view.View;
import android.widget.TabHost.OnTabChangeListener;
import android.widget.TabHost.TabContentFactory;
public class Main extends MapActivity implements OnTabChangeListener{
/** Called when the activity is first created. */
private static final String LIST_TAB_TAG = "List";
private static final String MAP_TAB_TAG = "Map";
MapView map;
ListView listView;
TabHost tabHost;
long start;
long stop;
int x, y;
MyLocationOverlay compass;
MyLocationOverlay MyLoc;
MapController controller;
GeoPoint touchedPoint;
Drawable d;
List<Overlay> overlayList;
CustomPinpoint custom;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
tabHost = (TabHost) findViewById(android.R.id.tabhost);
tabHost.setup();
listView = (ListView) findViewById(R.id.list);
listView.setEmptyView((TextView) findViewById(R.id.empty));
d = getResources().getDrawable(R.drawable.ic_launcher);
CustomPinpoint custom = new CustomPinpoint(d,Main.this);
listView.setAdapter(new ArrayAdapter<OverlayItem>(this, android.R.layout.simple_list_item_1, custom.pinpoints));
listView.setOnItemClickListener(new OnItemClickListener() {
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
GeoPoint geoPoint = ((OverlayItem) listView.getAdapter().getItem(position)).getPoint();
if(geoPoint != null) {
map.getController().animateTo(geoPoint);
tabHost.setCurrentTab(1);
}
}
});
map = (MapView) findViewById(R.id.mapview);
map.setBuiltInZoomControls(true);
map.postInvalidate();
Touch t = new Touch();
overlayList = map.getOverlays();
overlayList.add(t);
compass = new MyLocationOverlay(Main.this, map);
overlayList.add(compass);
controller = map.getController();
MyLoc = new MyLocationOverlay(Main.this, map);
overlayList.add(MyLoc);
map.postInvalidate();
MyLoc.runOnFirstFix(new Runnable() {
public void run() {
map.getController().animateTo(MyLoc.getMyLocation());
}
});
tabHost.addTab(tabHost.newTabSpec(LIST_TAB_TAG).setIndicator("List").setContent(new TabContentFactory() {
public View createTabContent(String arg0) {
return listView;
}
}));
tabHost.addTab(tabHost.newTabSpec(MAP_TAB_TAG).setIndicator("Map").setContent(new TabContentFactory() {
public View createTabContent(String arg0) {
return map;
}
}));
//HACK to get the list view to show up first,
// otherwise the mapview would be bleeding through and visible
tabHost.setCurrentTab(1);
tabHost.setCurrentTab(0);
}
@Override
protected void onPause() {
// TODO Auto-generated method stub
compass.disableCompass();
super.onPause();
MyLoc.disableMyLocation();
finish();
}
@Override
protected void onResume() {
// TODO Auto-generated method stub
compass.enableCompass();
super.onResume();
MyLoc.enableMyLocation();
}
@Override
protected boolean isRouteDisplayed() {
// TODO Auto-generated method stub
return false;
}
class Touch extends Overlay {
public boolean onTouchEvent(MotionEvent e, MapView m) {
if (e.getAction() == MotionEvent.ACTION_DOWN) {
start = e.getEventTime();
x = (int) e.getX();
y = (int) e.getY();
touchedPoint = map.getProjection().fromPixels(x, y);
}
if (e.getAction() == MotionEvent.ACTION_UP) {
stop = e.getEventTime();
}
if (stop - start > 1500) {
AlertDialog alert = new AlertDialog.Builder(Main.this).create();
alert.setTitle("Pick an option.");
alert.setButton(DialogInterface.BUTTON_POSITIVE,"Place a pinpoint.",
new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog,
int which) {
// TODO Auto-generated method stub
OverlayItem overlayItem = new OverlayItem(touchedPoint, "Pinpoint", "2nd String");
custom.insertPinpoint(overlayItem);
overlayList.add(custom);
}
});
alert.setButton(DialogInterface.BUTTON_NEUTRAL,"Get address.",
new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog,
int which) {
// TODO Auto-generated method stub
Geocoder geocoder = new Geocoder(getBaseContext(), Locale.getDefault());
try{
List<Address> address = geocoder.getFromLocation(touchedPoint.getLatitudeE6() /1E6, touchedPoint.getLongitudeE6()/1E6, 1);
if (address.size() > 0){
String display = "";
for (int i = 0; i < address.get(0).getMaxAddressLineIndex(); i++){
display += address.get(0).getAddressLine(i) + "\n";
}
Toast t3 = Toast.makeText(getBaseContext(), display, Toast.LENGTH_LONG);
t3.show();
}
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}finally{
}
}
});
alert.setButton(DialogInterface.BUTTON_NEGATIVE,"Toggle View", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int which) {
// TODO Auto-generated method stub
if (map.isSatellite()){
map.setSatellite(false);
}else{
map.setSatellite(true);
}
}
});
alert.show();
return true;
}
return false;
}
}
public void gpsCurrentLocation()
{
tabHost.setCurrentTab(1);
GeoPoint p = MyLoc.getMyLocation();
map.getController().animateTo(p);
}
// Menu XML file (menu.xml)
@Override
public boolean onCreateOptionsMenu(Menu menu)
{
MenuInflater menuInflater = getMenuInflater();
menuInflater.inflate(R.menu.activity_main, menu);
return true;
}
/**
* Event Handling for Individual menu item selected
* Identify single menu item by it's id
* */
@Override
public boolean onOptionsItemSelected(MenuItem item)
{
switch (item.getItemId())
{
case R.id.my_location:
Toast.makeText(Main.this, "Moving To Current location", Toast.LENGTH_SHORT).show();
gpsCurrentLocation();
return true;
default:
return super.onOptionsItemSelected(item);
}
}
public void onTabChanged(String tabId) {
// TODO Auto-generated method stub
}
}
答案 0 :(得分：0)
使用custom = new CustomPinpoint(d,Main.this);
而不是
CustomPinpoint custom = new CustomPinpoint(d,Main.this);