嗨，我有我的 aacplayer 应用程序，但是当我断开所有连接时，我的意思是 wifi + 移动数据并尝试打开它崩溃的应用程序没有打开，我想要做的是在主要活动中向用户显示一条消息，例如：Theres没有连接请重试。
我的应用程序是这样工作的：
我有一个列表视图，然后从 xml 加载许多广播电台的数据，然后当我点击其中一个时，它会打开 aac 播放器并正确播放。我也用于流式传输服务。
如何避免应用程序崩溃？
这是我的主要活动：
public class Principal extends Activity {
protected TextView title;
protected ImageView icon;
static final String URL = "http://www.streaming507.com/estaciones.xml";
static final String KEY_ESTACION = "estacion";
static final String KEY_ID = "id";
static final String KEY_NOMBRE = "nombre";
static final String KEY_WEB = "web";
static final String KEY_SHOUTCAST = "shoutcast";
static final String KEY_MINIATURA = "miniatura";
static final String KEY_LOGO = "logo";
private static final int DIALOG_ALERT = 10;
public static Activity handleToClose;
ListView list;
LazyAdapter adapter;
private Button botonactualizar;
public void actualizar() {
title = (TextView) findViewById(R.id.title);
icon = (ImageView) findViewById(R.id.icon);
ArrayList<HashMap<String, String>> songsList = new ArrayList<HashMap<String, String>>();
XMLParser parser = new XMLParser();
String xml = parser.getXmlFromUrl(URL);
Document doc = parser.getDomElement(xml);
NodeList nl = doc.getElementsByTagName(KEY_ESTACION);
for (int i = 0; i < nl.getLength(); i++) {
HashMap<String, String> map = new HashMap<String, String>();
Element e = (Element) nl.item(i);
map.put(KEY_ID, parser.getValue(e, KEY_ID));
map.put(KEY_NOMBRE, parser.getValue(e, KEY_NOMBRE));
map.put(KEY_WEB, parser.getValue(e, KEY_WEB));
map.put(KEY_SHOUTCAST, parser.getValue(e, KEY_SHOUTCAST));
map.put(KEY_MINIATURA, parser.getValue(e, KEY_MINIATURA));
map.put(KEY_LOGO, parser.getValue(e, KEY_LOGO));
songsList.add(map);
}
list = (ListView) findViewById(R.id.list);
adapter = new LazyAdapter(this, songsList);
list.setAdapter(adapter);
list.setOnItemClickListener(new OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> parent, View view,
int position, long id) {
String url = ((TextView) view.findViewById(R.id.shoutcast))
.getText().toString();
String logo = ((TextView) view.findViewById(R.id.logo))
.getText().toString();
try {
stopService(new Intent(view.getContext(), MyService.class));
} catch (Exception ex) {
}
Intent myIntent = new Intent(view.getContext(),
AACPlayerActivity.class);
myIntent.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP
| Intent.FLAG_ACTIVITY_SINGLE_TOP);
myIntent.putExtra("URL", url);
myIntent.putExtra("LOGO", logo);
startActivity(myIntent);
}
});
}
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
requestWindowFeature(Window.FEATURE_CUSTOM_TITLE);
setContentView(R.layout.main);
getWindow().setFeatureInt(Window.FEATURE_CUSTOM_TITLE,
R.layout.window_title);
handleToClose = this;
actualizar();
botonactualizar = (Button)findViewById(R.id.botonactualizar);
botonactualizar.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View vw) {
actualizar();
Toast.makeText(Principal.this, "Lista de estaciones actualizada",
Toast.LENGTH_SHORT).show();
}
});
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
MenuInflater menuInflater = getMenuInflater();
menuInflater.inflate(R.layout.menu_opciones1, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
switch (item.getItemId()) {
case R.id.menu_actualizar:
actualizar();
Toast.makeText(Principal.this, "Lista de estaciones actualizada",
Toast.LENGTH_SHORT).show();
return true;
case R.id.menu_salir:
showDialog(DIALOG_ALERT);
return true;
default:
return super.onOptionsItemSelected(item);
}
}
@Override
protected Dialog onCreateDialog(int id) {
switch (id) {
case DIALOG_ALERT:
Builder builder = new AlertDialog.Builder(this);
builder.setMessage("Desea salir de la aplicacion?");
builder.setCancelable(true);
builder.setPositiveButton("Si", new OkOnClickListener());
builder.setNegativeButton("No", new CancelOnClickListener());
AlertDialog dialog = builder.create();
dialog.show();
}
return super.onCreateDialog(id);
}
private final class CancelOnClickListener implements
DialogInterface.OnClickListener {
public void onClick(DialogInterface dialog, int which) {
}
}
private final class OkOnClickListener implements
DialogInterface.OnClickListener {
public void onClick(DialogInterface dialog, int which) {
finish();
stopService(new Intent(Principal.this, MyService.class));
String ns = Context.NOTIFICATION_SERVICE;
NotificationManager mNotificationManager = (NotificationManager) getSystemService(ns);
mNotificationManager.cancel(1);
}
}
}
我知道有一个叫做connectivitymanager的东西，但我不知道在我的主要活动或流服务中我必须在哪里设置它，所以当我在没有互联网的情况下打开应用程序时，我可以看到一条消息：请重试。然后是一个刷新按钮，所以如果互联网打开，那么我可以从网页的 xml 加载列表。
谢谢你。
编辑：
当我在没有互联网连接的情况下打开应用程序时出现此错误
ava.net.UnknownHostException: Unable to resolve host "www.mydomain.com": No address associated with hostname
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.spoledge.aacplayer/com.spoledge.aacplayer.Principal}: java.lang.NullPointerException