我有一个Android应用程序，使用计时器任务每3分钟向数据库提交一次。即使用户最小化应用程序，也会假定计时器持续存在。如果我将焦点更改为另一个应用程序，然后更改回来一切正常，但如果我按下主页按钮然后按应用程序图标另一个计时器任务启动。有谁能解释为什么？
package temp;
import android.app.Activity;
import android.content.Context;
import android.content.Intent;
import android.location.Location;
import android.net.ConnectivityManager;
import android.net.NetworkInfo;
import android.net.Uri;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.ImageButton;
import android.widget.TextView;
import android.widget.Toast;
import android.location.Geocoder;
import com.google.android.gms.common.ConnectionResult;
import com.google.android.gms.common.GooglePlayServicesUtil;
import com.google.android.gms.common.api.GoogleApiClient;
import com.google.android.gms.common.api.PendingResult;
import com.google.android.gms.common.api.Status;
import com.google.android.gms.location.LocationListener;
import com.google.android.gms.location.LocationRequest;
import com.google.android.gms.location.LocationServices;
import java.text.DateFormat;
import java.util.Date;
import java.util.Locale;
public class MainActivity extends Activity implements LocationListener,
GoogleApiClient.ConnectionCallbacks, GoogleApiClient.OnConnectionFailedListener{
private Button bLogout, bWebsite;
private ImageButton bLogData;
private TextView etLabel;
private UserLocalStore userLocalStore;
private String mLastUpdateTime;
private LocationRequest mLocationRequest;
private GoogleApiClient mGoogleApiClient;
private static final String TAG = "MainActivity";
private static final long INTERVAL = 1000 * 15;
private static final long FATEST_INTERVAL = 1000 * 30;
private Geocoder geocoder;
AddressOps addressOps;
TimerUpdate timerUpdate;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Log.e(TAG, "On Create . . . . .");
if(!isGooglePlayServicesAvailable()){
startActivity(new Intent(MainActivity.this, login.class));
finish();
Toast.makeText(getApplicationContext(), "Please update GooglePlay Servies to use this Application", Toast.LENGTH_LONG).show();
}else {
mGoogleApiClient = new GoogleApiClient.Builder(this)
.addApi(LocationServices.API)
.addConnectionCallbacks(this)
.addOnConnectionFailedListener(this)
.build();
createLocationRequest();
userLocalStore = new UserLocalStore(this);
this.geocoder = new Geocoder(MainActivity.this, Locale.getDefault());
addressOps = new AddressOps(this.geocoder);
// if(this.timerUpdate == null && authenticate() == true) {
// this.timerUpdate = new TimerUpdate(this, addressOps);
// timerUpdate.startTimer();
// }
etLabel = (TextView) findViewById(R.id.etEmailLabel);
bLogout = (Button) findViewById(R.id.bLogout);
bLogData = (ImageButton) findViewById(R.id.DataLog);
bWebsite = (Button) findViewById(R.id.website);
bLogData.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View arg0) {
String pressStatus = "3";
timerUpdate.update(pressStatus);
}
});
bLogout.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View arg0) {
userLocalStore.clearuserData();
userLocalStore.setUserLoggedIn(false);
timerUpdate.stopTimerTask();
startActivity(new Intent(MainActivity.this, login.class));
finish();
}
});
bWebsite.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View arg0) {
Intent browserIntent = new Intent(Intent.ACTION_VIEW, Uri.parse("http://temp.com"));
startActivity(browserIntent);
}
});
}
}
private void displayUserDetails(){
User user = userLocalStore.getLoggedInUser();
String userdisplay = "Logged in as: " + user.username;
etLabel.setText(userdisplay);
}
private boolean authenticate(){
return userLocalStore.getUserLoggedIn();
}
private boolean isNetworkAvailable() {
ConnectivityManager connectivityManager = (ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE);
NetworkInfo activeNetworkInfo = connectivityManager.getActiveNetworkInfo();
Log.e(TAG, "Network Check");
return activeNetworkInfo != null && activeNetworkInfo.isConnected();
}
private boolean isGooglePlayServicesAvailable() {
int status = GooglePlayServicesUtil.isGooglePlayServicesAvailable(this);
if (ConnectionResult.SUCCESS == status) {
return true;
} else {
GooglePlayServicesUtil.getErrorDialog(status, this, 0).show();
return false;
}
}
protected void createLocationRequest(){
mLocationRequest = new LocationRequest();
mLocationRequest.setInterval(INTERVAL);
mLocationRequest.setFastestInterval(FATEST_INTERVAL);
mLocationRequest.setPriority(LocationRequest.PRIORITY_HIGH_ACCURACY);
}
@Override
public void onConnected(Bundle bundle) {
Log.e(TAG, "onConnected: Connected - " + mGoogleApiClient.isConnected());
startLocationUpdates();
}
protected void startLocationUpdates() {
PendingResult<Status> pendingResult = LocationServices.FusedLocationApi.requestLocationUpdates(mGoogleApiClient, mLocationRequest, this);
Log.e(TAG, "Location update started ");
}
@Override
public void onConnectionSuspended(int i) {
stopLocationUpdates();
Log.e(TAG, "On Connection Suspended " + mGoogleApiClient.isConnected());
Toast.makeText(getApplicationContext(), "No Network Connection", Toast.LENGTH_LONG).show();
}
@Override
public void onConnectionFailed(ConnectionResult connectionResult) {
Log.e(TAG, "Connection failed " + connectionResult.toString());
stopLocationUpdates();
Log.e(TAG, "onConnectionFailed " + mGoogleApiClient.isConnected());
Toast.makeText(getApplicationContext(), "No Network Connection", Toast.LENGTH_LONG).show();
}
@Override
public void onLocationChanged(Location location) {
Log.e(TAG, "Firing onLocationChanged.........");
if(this.timerUpdate != null) {
timerUpdate.location = location;
}else{
Log.e(TAG, "Timer is null");
}
mLastUpdateTime = DateFormat.getTimeInstance().format(new Date());
}
protected void stopLocationUpdates() {
LocationServices.FusedLocationApi.removeLocationUpdates(mGoogleApiClient, this);
Log.e(TAG, "Location update stopped");
}
@Override
protected void onPause() {
super.onPause();
Log.e(TAG, "MainActivity Paused");
}
@Override
public void onResume() {
super.onResume();
Log.e(TAG, "MainActivity Resumed");
if (mGoogleApiClient.isConnected()) {
if(!isGooglePlayServicesAvailable()){
startActivity(new Intent(MainActivity.this, login.class));
Toast.makeText(getApplicationContext(), "Please update GooglePlay Servies to use this Application", Toast.LENGTH_LONG).show();
finish();
}
}
}
@Override
public void onStart() {
super.onStart();
if(authenticate() == true){
displayUserDetails();
if(this.timerUpdate == null) {
this.timerUpdate = new TimerUpdate(this, addressOps);
Log.e(TAG, "Timer created");
timerUpdate.startTimer();
}
}else{
startActivity(new Intent(MainActivity.this, login.class));
finish();
}
mGoogleApiClient.connect();
Log.e(TAG, "MainActivity Started, GoogleApi Connection: " + mGoogleApiClient.isConnected());
}
@Override
public void onStop() {
super.onStop();
Log.e(TAG, "MainActivity Stopped");
}
}
继承我的timertask课程
package temp;
import android.content.Context;
import android.location.Location;
import android.net.ConnectivityManager;
import android.net.NetworkInfo;
import android.os.Handler;
import android.util.Log;
import android.widget.Toast;
import java.util.Timer;
import java.util.TimerTask;
public class TimerUpdate {
private Timer timer;
private TimerTask timertask;
public boolean timerScheduled = false;
private final Handler handler = new Handler();
private static final String TAG = "UpdateTimer";
AddressOps addressOps;
private Context mainContext;
private UserLocalStore userLocalStore;
public Location location;
public TimerUpdate(Context context, AddressOps ops){
initializeTimerTask();
this.mainContext = context;
this.addressOps = ops;
userLocalStore = new UserLocalStore(context);
}
private void initializeTimerTask(){
timertask = new TimerTask() {
public void run(){
handler.post(new Runnable(){
public void run(){
Log.e(TAG, "TimerTask Ran");
String status = "5";
update(status);
}
});
}
};
}
public void startTimer(){
timer = new Timer();
timer.schedule(timertask, 1000 * 30, 1000 * 60 * 3);
timerScheduled = true;
Log.e(TAG, "Start Schedule created");
}
public void stopTimerTask(){
if (timer != null){
timer.cancel();
timer = null;
Log.e(TAG, "Timer Stopped");
}
}
public void update(String status) {
Log.e(TAG, "Update initiated .............");
if (location != null) {
double lat = location.getLatitude();
double lng = location.getLongitude();
if(isNetworkAvailable()){
String address = addressOps.getAddressString(lng, lat);
if(address != null) {
User user = userLocalStore.getLoggedInUser();
ServerRequest request = new ServerRequest(this.mainContext);
request.storeLocationInBackground(lat, lng, user.username, address, status);
Toast.makeText(this.mainContext, "Longitude: " + lng + "\nLatitude: "
+ lat + "\nAddress: " + address, Toast.LENGTH_SHORT).show();
}else{
Toast.makeText(this.mainContext, "Unable to retrieve Address", Toast.LENGTH_SHORT).show();
}
}else{
Toast.makeText(this.mainContext, "No Network Connection" + "\nLatitude: " + lat
+ "\nLongitude: " + lng, Toast.LENGTH_LONG).show();
}
} else {
Log.e(TAG, "There is no current Location Data in Update");
Toast.makeText(this.mainContext, "There is no current Location Data ....", Toast.LENGTH_SHORT).show();
}
}
private boolean isNetworkAvailable() {
ConnectivityManager connectivityManager = (ConnectivityManager)mainContext.getSystemService(Context.CONNECTIVITY_SERVICE);
NetworkInfo activeNetworkInfo = connectivityManager.getActiveNetworkInfo();
Log.e(TAG, "Network Check");
return activeNetworkInfo != null && activeNetworkInfo.isConnected();
}
}
因此，正如@Robert在评论中建议的那样，这是因为你的TimerTask实例与Activity实例绑定。当您启动另一个Activity实例时（通过点击启动器图标启动您的应用程序），将创建一个新的TimerTask实例。如果你需要你的TimerTask独立于活动，那么你需要一个Service。
当您重新启动应用程序时，MainActivity将通过onCreate和onStart，并在onStart中启动计时器。