BroadcastReceiver - 无法从关闭或后台应用程序启动活动

Question

我正在尝试使用 AlarmManager 和 BroadcastReceiver 从已关闭的应用程序中启动活动。即使应用程序关闭或在后台，“已收到”调试消息也会显示，这意味着 AlarmManager 正在按我想要的方式工作。但 CameraActivity 仅在应用程序处于活动状态时启动。 任何人都知道为什么它不起作用？这是我的（部分）代码：

主活动：

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        ...

        Intent intent = new Intent(this, AlarmReceiver.class);
        PendingIntent pendingIntent = PendingIntent.getBroadcast(this, 0, intent, PendingIntent.FLAG_UPDATE_CURRENT);

        AlarmManager alarmManager = (AlarmManager) getSystemService(Context.ALARM_SERVICE);

        alarmManager.setRepeating(
                AlarmManager.RTC_WAKEUP,
                startTimeStamp,
                intervalTime,
                pendingIntent);

        Log.i("########################DEBUG", "started");
    }
}

报警接收器

public class AlarmReceiver extends BroadcastReceiver {

    @Override
    public void onReceive(Context context, Intent intent) {
        Log.i("########################DEBUG", "received");

        Intent launchIntent = new Intent(context, CameraActivity.class);
        launchIntent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK | Intent.FLAG_ACTIVITY_BROUGHT_TO_FRONT);
        context.startActivity(launchIntent);

        /* Tried this too, didn't work
        PackageManager packageManager = context.getPackageManager();
        Intent launchIntent = packageManager.getLaunchIntentForPackage(CameraActivity.class.getName());
        context.startActivity(launchIntent);*/
    }
}

相机活动

public class CameraActivity extends AppCompatActivity {

    private final int CAMERA_REQUEST = 1;

    private ImageView image;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_camera);

        image = findViewById(R.id.imageview);

        Intent cameraIntent = new Intent(MediaStore.ACTION_IMAGE_CAPTURE);
        //startActivityForResult(cameraIntent, CAMERA_REQUEST);
    }

    @Override
    protected void onActivityResult(int requestCode, int resultCode, @Nullable Intent data) {
        if (resultCode == RESULT_OK && requestCode == CAMERA_REQUEST) {
            Bitmap photo = (Bitmap) data.getExtras().get("data");
            image.setImageBitmap(photo);
        }
    }
}

manifest.xml

    <application

        ...

        <activity android:name=".CameraActivity">
        </activity>
        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>

        <receiver android:name=".AlarmReceiver" />
    </application>

提前致谢！

Answer 1

根据 Android 10 中的 documentation，当您的应用在后台运行时，您无法启动 Activity，除非在涉及用户交互的非常有限的情况下。

文档指南提供通知作为从后台启动活动的替代方法。然后，本指南列出了限制不适用的具体情况。它建议显示Time-sensitive notification 以向用户提供紧急信息，而不是直接启动活动或全屏意图。