按下android按钮“最近”后的活动生命周期创建新活动但不破坏旧活动

Question

当我按下 android 按钮“recents”并再次选择我的应用程序以返回应用程序时，MapsActivity 的生命周期再次执行 onCreate 并创建一个新的 MapsActivity 实例。

没关系，但旧的 MapsActivity 仍在后台运行，这是一个问题，因为两个 MapsActivity 都有计数器，并且仍在运行并使用相同变量中的不同值进行计数，例如独立的新变量。

计数器位于 onLocationChanged() 中并称为“时钟”。 onLocationChanged() 每 5 秒自动更新一次。

示例： 计数器正在运行：1, 2, 3, 4, 5, ... 此时我按下android按钮“recent”（系统执行onCreate） 计数器仍然这样运行：6、1、7、2、8、3，... 此时再次按下 android 按钮“最近”（执行 onCreate） 计数器仍在运行：9、4、1、10、5、2、11、6、3，...

我想 MapsActivity 的生命周期不会破坏旧的活动。

我只需要一个顺序计数器运行，我猜旧的 MapsActivity 必须死:)

有什么办法可以解决我的问题吗？非常感谢！

在 manifest.xml 下方

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.sasse.myapplication">

    <uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">

        <meta-data
            android:name="com.google.android.geo.API_KEY"
            android:value="@string/google_maps_key" />

        <activity
            android:name=".MapsActivity"
            android:label="@string/title_activity_maps">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>

布局activity_maps.xml

<fragment xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:map="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/map"
    android:name="com.google.android.gms.maps.SupportMapFragment"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="com.example.sasse.myapplication.MapsActivity" />

地图活动

package com.example.sasse.myapplication;

import android.*;
import android.Manifest;
import android.content.pm.PackageManager;
import android.location.Location;
import android.os.Build;
import android.support.annotation.NonNull;
import android.support.v4.app.ActivityCompat;
import android.support.v4.app.FragmentActivity;
import android.os.Bundle;
import android.support.v4.content.ContextCompat;
import android.util.Log;
import android.widget.Toast;

import com.google.android.gms.common.ConnectionResult;
import com.google.android.gms.common.api.GoogleApiClient;
import com.google.android.gms.common.api.GoogleApiClient.ConnectionCallbacks;
import com.google.android.gms.common.api.GoogleApiClient.OnConnectionFailedListener;
import com.google.android.gms.location.LocationListener;
import com.google.android.gms.location.LocationRequest;
import com.google.android.gms.location.LocationServices;
import com.google.android.gms.maps.CameraUpdateFactory;
import com.google.android.gms.maps.GoogleMap;
import com.google.android.gms.maps.OnMapReadyCallback;
import com.google.android.gms.maps.SupportMapFragment;
import com.google.android.gms.maps.model.LatLng;
import com.google.android.gms.maps.model.MarkerOptions;

public class MapsActivity extends FragmentActivity implements LocationListener, ConnectionCallbacks, OnConnectionFailedListener, OnMapReadyCallback {

    private static final String TAG = "MapsActivity";
    private GoogleMap mMap;
    protected GoogleApiClient mGoogleApiClient;
    protected LocationRequest mLocationRequest;
    public int clock = 0;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_maps);
        // Obtain the SupportMapFragment and get notified when the map is ready to be used.
        SupportMapFragment mapFragment = (SupportMapFragment) getSupportFragmentManager()
                .findFragmentById(R.id.map);
        mapFragment.getMapAsync(this);
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
            checkLocationPermission();
        }
    }

    @Override
    public void onMapReady(GoogleMap googleMap) {
        mMap = googleMap;

        // Add a marker in Sydney and move the camera
        LatLng sydney = new LatLng(-34, 151);
        mMap.addMarker(new MarkerOptions().position(sydney).title("Marker in Sydney"));
        mMap.moveCamera(CameraUpdateFactory.newLatLng(sydney));
        //Initialize Google Play Services
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
            if (ContextCompat.checkSelfPermission(this,
                    android.Manifest.permission.ACCESS_FINE_LOCATION)
                    == PackageManager.PERMISSION_GRANTED) {
                buildGoogleApiClient();
                mMap.setMyLocationEnabled(true);
            }
        } else {
            buildGoogleApiClient();
            mMap.setMyLocationEnabled(true);
        }

    }

    public void onLocationChanged(Location location) {

        clock++;
        if (clock>=10) {

            Toast.makeText(this, "clock : "+clock, Toast.LENGTH_SHORT).show();
            clock=0;
        }
        Log.i(TAG, "= = = = = >>> clock : "+clock);
    }

    // ---------------------------------------------------------------------------------------------
    // ---------------- VERIFICAÇÃO DA CONEXÃO COM O SERVIDOR DO GOOGLE MAPS-----------------------
    // ---------------------------------------------------------------------------------------------
    public static final int MY_PERMISSIONS_REQUEST_LOCATION = 99;

    public boolean checkLocationPermission() {
        if (ContextCompat.checkSelfPermission(this,
                android.Manifest.permission.ACCESS_FINE_LOCATION)
                != PackageManager.PERMISSION_GRANTED) {

            // Asking user if explanation is needed
            if (ActivityCompat.shouldShowRequestPermissionRationale(this,
                    android.Manifest.permission.ACCESS_FINE_LOCATION)) {

                // Show an explanation to the user *asynchronously* -- don't block
                // this thread waiting for the user's response! After the user
                // sees the explanation, try again to request the permission.

                //Prompt the user once explanation has been shown
                ActivityCompat.requestPermissions(this,
                        new String[]{android.Manifest.permission.ACCESS_FINE_LOCATION},
                        MY_PERMISSIONS_REQUEST_LOCATION);
            } else {
                // No explanation needed, we can request the permission.
                ActivityCompat.requestPermissions(this,
                        new String[]{android.Manifest.permission.ACCESS_FINE_LOCATION},
                        MY_PERMISSIONS_REQUEST_LOCATION);
            }
            return false;
        } else {
            return true;
        }
    }

    public void onRequestPermissionsResult(int requestCode, @NonNull String permissions[], @NonNull int[] grantResults) {
        switch (requestCode) {
            case MY_PERMISSIONS_REQUEST_LOCATION: {
                // If request is cancelled, the result arrays are empty.
                if (grantResults.length > 0 && grantResults[0] == PackageManager.PERMISSION_GRANTED) {
                    // permission was granted. Do the
                    // contacts-related task you need to do.
                    if (ContextCompat.checkSelfPermission(this,
                            android.Manifest.permission.ACCESS_FINE_LOCATION)
                            == PackageManager.PERMISSION_GRANTED) {
                        if (mGoogleApiClient == null) {
                            buildGoogleApiClient();
                        }
                        mMap.setMyLocationEnabled(true);
                    }
                } else {
                    // Permission denied, Disable the functionality that depends on this permission.
                    Toast.makeText(this, "permission denied", Toast.LENGTH_LONG).show();
                }
            }
            // other 'case' lines to check for other permissions this app might request.
            // You can add here other case statements according to your requirement.
        }
    }

    protected synchronized void buildGoogleApiClient() {
        mGoogleApiClient = new GoogleApiClient.Builder(this)
                .addConnectionCallbacks(this)
                .addOnConnectionFailedListener(this)
                .addApi(LocationServices.API)
                .build();
        mGoogleApiClient.connect();
    }

    public void onConnected(Bundle bundle) {
        mLocationRequest = new LocationRequest();
        mLocationRequest.setInterval(5000);
        mLocationRequest.setFastestInterval(5000);
        mLocationRequest.setPriority(LocationRequest.PRIORITY_BALANCED_POWER_ACCURACY);
        if (ContextCompat.checkSelfPermission(this,
                Manifest.permission.ACCESS_FINE_LOCATION)
                == PackageManager.PERMISSION_GRANTED) {
            LocationServices.FusedLocationApi.requestLocationUpdates(mGoogleApiClient, mLocationRequest, this);
        }
    }

    public void onConnectionSuspended(int i) {
    }

    public void onConnectionFailed(@NonNull ConnectionResult connectionResult) {
    }
}

Answer 1

尝试使用 launchMode="singleTop" 进行活动