Java 对象类的空引用？交通服务等级？
我曾尝试在android的状态栏中设置网络速度。我已成功删除错误，但应用程序崩溃。我试图在我的示例项目中实现它。 到目前为止，我已经从TrafficeService类中重新验证了错误。我想从MainActivity调用它，但它在android studio中将错误显示为空引用 MainActivity.javaJava 对象类的空引用？交通服务等级？,java,android,android-studio,android-layout,Java,Android,Android Studio,Android Layout,我曾尝试在android的状态栏中设置网络速度。我已成功删除错误，但应用程序崩溃。我试图在我的示例项目中实现它。 到目前为止，我已经从TrafficeService类中重新验证了错误。我想从MainActivity调用它，但它在android studio中将错误显示为空引用 MainActivity.java package com.example.myapplication; import androidx.appcompat.app.AppCompatActivity; import
package com.example.myapplication;
import androidx.appcompat.app.AppCompatActivity;
import android.content.ComponentName;
import android.content.Intent;
import android.content.ServiceConnection;
import android.os.Bundle;
import android.os.IBinder;
public class MainActivity extends AppCompatActivity {
private boolean isBounded;
private TrafficService backgroundService;
private final ServiceConnection mConnection = new ServiceConnection() {
public void onServiceDisconnected(ComponentName name) {
isBounded = false;
backgroundService = null;
}
public void onServiceConnected(ComponentName name, IBinder service) {
isBounded = true;
TrafficService.LocalBinder mLocalBinder = (TrafficService.LocalBinder) service;
backgroundService = mLocalBinder.getServerInstance();
}
};
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Intent serviceIntent = new Intent(getApplicationContext(), TrafficService.class);
startService(serviceIntent);
bindService(serviceIntent, mConnection, BIND_AUTO_CREATE);
backgroundService.showNotification();
}
@Override
protected void onStop() {
super.onStop();
if (isBounded) {
unbindService(mConnection);
isBounded = false;
}
}
}
package com.example.myapplication;
import android.annotation.SuppressLint;
import android.app.NotificationManager;
import android.app.PendingIntent;
import android.app.Service;
import android.content.BroadcastReceiver;
import android.content.ComponentName;
import android.content.Context;
import android.content.Intent;
import android.content.IntentFilter;
import android.content.SharedPreferences;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Color;
import android.net.ConnectivityManager;
import android.net.NetworkInfo;
import android.net.TrafficStats;
import android.net.wifi.WifiInfo;
import android.net.wifi.WifiManager;
import android.os.Binder;
import android.os.Build;
import android.os.Handler;
import android.os.IBinder;
import android.os.Message;
import android.os.PowerManager;
import android.preference.PreferenceManager;
//import android.support.v4.app.NotificationCompat;
import android.telephony.TelephonyManager;
import android.text.format.Formatter;
import android.util.Log;
import androidx.core.app.NotificationCompat;
/**
* Main service class that monitors the network speed and updates the notification every second
*/
public class TrafficService extends Service {
/**
* The constant defining the identifier of the notification that is to be shown
*/
private static final int ID = 9000;
/**
* The identifier if the component that open from the settings activity
*/
private static final String CMP = "com.android.settings.Settings$DataUsageSummaryActivity";
/**
* The instance of the handler that updates the notification
*/
private static NotificationHandler hndNotifier;
/**
* The instance of the manager of the connectivity services
*/
private static ConnectivityManager mgrConnectivity;
/**
* The instance of the manager of the notification services
*/
private static NotificationManager mgrNotifications;
/**
* The instance of the manager of the wireless services
*/
private static WifiManager mgrWireless;
/**
* The instance of the manager of the telephony services
*/
private static TelephonyManager mgrTelephony;
/**
* The instance of the notification builder to rebuild the notification
*/
private static NotificationCompat.Builder notBuilder;
/**
* The instance of the binder class used by the activity
*/
private final IBinder mBinder = new LocalBinder();
/**
* The instance of the broadcast receiver to handle intents
*/
private BroadcastReceiver recScreen;
/**
* The instance of the broadcast receiver to handle power saver mode intents
*/
//private final BroadcastReceiver recSaver = new PowerReceiver();
/**
* Initializes the service by getting instances of service managers and mainly setting up the
* receiver to receive all the necessary intents that this service is supposed to handle.
*/
@Override
public void onCreate() {
Log.i("HardwareService", "Creating the hardware service");
super.onCreate();
final SharedPreferences settings = PreferenceManager.getDefaultSharedPreferences(getApplicationContext());
Intent ittSettings = new Intent();
ittSettings.setComponent(new ComponentName("com.android.settings", CMP));
PendingIntent pitSettings = PendingIntent.getActivity(this, 0, ittSettings, 0);
notBuilder = new NotificationCompat.Builder(this);
notBuilder.setSmallIcon(R.drawable.wkb000);
notBuilder.setContentIntent(pitSettings);
notBuilder.setOngoing(true);
notBuilder.setWhen(0);
notBuilder.setOnlyAlertOnce(true);
notBuilder.setPriority(Integer.MAX_VALUE);
notBuilder.setCategory(NotificationCompat.CATEGORY_SERVICE);
notBuilder.setLocalOnly(true);
setColor(settings.getInt("color", Color.TRANSPARENT));
visibilityPublic(settings.getBoolean("lockscreen", true));
Log.d("HardwareService", "Setting up the service manager and the broadcast receiver");
mgrConnectivity = (ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE);
mgrNotifications = (NotificationManager) getSystemService(NOTIFICATION_SERVICE);
mgrWireless = (WifiManager) getApplicationContext().getSystemService(Context.WIFI_SERVICE);
mgrTelephony = (TelephonyManager) getSystemService(Context.TELEPHONY_SERVICE);
hndNotifier = new NotificationHandler(getApplicationContext());
if (settings.getBoolean("enabled", true)) {
Log.d("HardwareService", "Screen on; showing the notification");
hndNotifier.sendEmptyMessage(1);
}
recScreen = new BroadcastReceiver() {
/**
* Handles the screen-on and the screen off intents to enable or disable the notification.
* We don't want to show the notification if the screen is off.
*/
@Override
public void onReceive(Context ctcContext, Intent ittIntent) {
if (ittIntent.getAction().equalsIgnoreCase(Intent.ACTION_SCREEN_OFF)) {
Log.d("TrafficService", "Screen off; hiding the notification");
hndNotifier.removeMessages(1);
mgrNotifications.cancel(ID);
} else if (ittIntent.getAction().equalsIgnoreCase(Intent.ACTION_SCREEN_ON)) {
Log.d("TrafficService", "Screen on; showing the notification");
connectivityUpdate();
} else if (ittIntent.getAction().equalsIgnoreCase(Intent.ACTION_AIRPLANE_MODE_CHANGED)) {
if (ittIntent.getBooleanExtra("state", false)) {
Log.d("TrafficService", "Airplane mode; hiding the notification");
hndNotifier.removeMessages(1);
hndNotifier.sendEmptyMessage(1);
} else {
Log.d("TrafficService", "Airplane mode; showing the notification");
connectivityUpdate();
}
} else {
Log.d("TrafficService", "Connectivity change; updating the notification");
connectivityUpdate();
}
}
};
IntentFilter ittScreen = new IntentFilter();
ittScreen.addAction(Intent.ACTION_SCREEN_ON);
ittScreen.addAction(Intent.ACTION_SCREEN_OFF);
ittScreen.addAction(Intent.ACTION_AIRPLANE_MODE_CHANGED);
ittScreen.addAction(ConnectivityManager.CONNECTIVITY_ACTION);
registerReceiver(recScreen, ittScreen);
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
IntentFilter ittSaver = new IntentFilter();
ittScreen.addAction(PowerManager.ACTION_POWER_SAVE_MODE_CHANGED);
//registerReceiver(recSaver, ittSaver);
}
}
/**
* Updates the notification with the new connectivity information. This method determines the type
* of connectivity and updates the notification with the network type and name. If there is no
* information about the active network, this will suppress the notification.
*/
private void connectivityUpdate() {
NetworkInfo nifNetwork = mgrConnectivity.getActiveNetworkInfo();
if (nifNetwork != null && nifNetwork.isConnectedOrConnecting()) {
Log.d("TrafficService", "Network connected; showing the notification");
if (nifNetwork.getType() == ConnectivityManager.TYPE_WIFI) {
Log.d("TrafficService", "Connected to a wireless network");
WifiInfo wifInfo = mgrWireless.getConnectionInfo();
if (wifInfo != null && !wifInfo.getSSID().trim().isEmpty()) {
Log.d("TrafficService", wifInfo.getSSID());
notBuilder.setContentTitle(getString(R.string.wireless));
notBuilder.setContentText(wifInfo.getSSID().replaceAll("^\"|\"$", ""));
showNotification();
} else {
Log.d("TrafficService", "Unknown network without SSID");
hideNotification();
}
} else {
Log.d("TrafficService", "Connected to a cellular network");
if (!mgrTelephony.getNetworkOperatorName().trim().isEmpty()) {
Log.d("TrafficService", mgrTelephony.getNetworkOperatorName());
notBuilder.setContentTitle(getString(R.string.cellular));
notBuilder.setContentText(mgrTelephony.getNetworkOperatorName());
showNotification();
} else {
Log.d("TrafficService", "Unknown network without IMSI");
hideNotification();
}
}
} else {
Log.d("TrafficService", "Network disconnected; hiding the notification");
hideNotification();
}
}
/**
* Called when the service is being stopped. It doesn't do much except clear the message queue of
* the handler, hides the notification and unregisters the receivers.
*/
@Override
public void onDestroy() {
Log.d("HardwareService", "Stopping the hardware service");
unregisterReceiver(recScreen);
//unregisterReceiver(recSaver);
hndNotifier.removeMessages(1);
mgrNotifications.cancel(ID);
}
/**
* Helper method that shows the notification by sending the handler a message and building the
* notification. This is invoked when the preference is toggled.
*/
public void showNotification() {
Log.d("HardwareService", "Showing the notification");
mgrNotifications.notify(ID, notBuilder.build());
hndNotifier.removeMessages(1);
hndNotifier.sendEmptyMessage(1);
}
/**
* Helper method that hides the notification by clearing the handler messages and cancelling the
* notification. This is invoked when the preference is toggled.
*/
public void hideNotification() {
Log.d("HardwareService", "Hiding the notification");
mgrNotifications.cancel(ID);
hndNotifier.removeMessages(1);
}
/**
* Helper method that toggles the visibility of the notification on the locksreen depending on the
* value of the preference in the activity
*
* @param visibility A boolean value indicating whether the notification should be visible on the
* lockscreen
*/
public void visibilityPublic(Boolean visibility) {
if (visibility) {
notBuilder.setVisibility(NotificationCompat.VISIBILITY_PUBLIC);
} else {
notBuilder.setVisibility(NotificationCompat.VISIBILITY_SECRET);
}
}
/**
* Helper method that sets the background color of the notification icon by parsing the RGB value
* into an int.
*
* @param color The internal int representation of the RGB color to set as the background colour
*/
public void setColor(Integer color) {
notBuilder.setColor(color);
}
/**
* Binder method to allow the settings activity to bind to the service so the notification can be
* configured and updated while the activity is being toggles.
*
* @see android.app.Service#onBind(android.content.Intent)
*/
@Override
public IBinder onBind(Intent intReason) {
return mBinder;
}
/**
* The handler class that runs every second to update the notification with the network speed. It
* also runs every minute to save the amount of data-transferred to the preferences.
*/
private static class NotificationHandler extends Handler {
/**
* The instance of the context of the parent service
*/
private final Context ctxContext;
/**
* The value of the amount of data transferred in the previous invocation of the method
*/
private long lngPrevious = 0L;
/**
* Simple constructor to initialize the initial value of the previous
*/
@SuppressLint("CommitPrefEdits")
public NotificationHandler(Context ctxContext) {
this.ctxContext = ctxContext;
}
/**
* Handler method that updates the notification icon with the current speed. It is a very
* hackish method. We have icons for 1 KB/s to 999 KB/s and 1.0 MB/s to 99.9 MB/s. Every time
* the method is invoked, we get the amount of data transferred. By subtracting this value with
* the previous value, we get the delta. Since this method is invoked every second, this delta
* value indicates the b/s. However, we need to convert this value into KB/s for values under 1
* MB/s and we need to convert the value to MB/s for values over 1 MB/s. Since all our icon
* images are numbered sequentially we can assume that the R class generated will contain the
* integer references of the drawables in the sequential order.
*/
@Override
public void handleMessage(Message msgMessage) {
TrafficService.hndNotifier.sendEmptyMessageDelayed(1, 1000L);
long lngCurrent = TrafficStats.getTotalRxBytes() + TrafficStats.getTotalTxBytes();
int lngSpeed = (int) (lngCurrent - lngPrevious);
lngPrevious = lngCurrent;
try {
if (lngSpeed < 1024) {
TrafficService.notBuilder.setSmallIcon(R.drawable.wkb000);
updateIcon(R.drawable.wkb000);
} else if (lngSpeed < 1048576L) {
TrafficService.notBuilder.setSmallIcon(R.drawable.wkb000 + (int) (lngSpeed / 1024L));
updateIcon(R.drawable.wkb000 + (int) (lngSpeed / 1024L));
if (lngSpeed > 1022976) {
TrafficService.notBuilder.setSmallIcon(R.drawable.wkb000 + 1000);
updateIcon(R.drawable.wkb000 + 1000);
}
} else if (lngSpeed <= 10485760) {
TrafficService.notBuilder.setSmallIcon(990 + R.drawable.wkb000
+ (int) (0.5D + (double) (10F * ((float) lngSpeed / 1048576F))));
updateIcon(990 + R.drawable.wkb000
+ (int) (0.5D + (double) (10F * ((float) lngSpeed / 1048576F))));
} else if (lngSpeed <= 103809024) {
TrafficService.notBuilder.setSmallIcon(1080 + R.drawable.wkb000
+ (int) (0.5D + (double) ((float) lngSpeed / 1048576F)));
updateIcon(1080 + R.drawable.wkb000
+ (int) (0.5D + (double) ((float) lngSpeed / 1048576F)));
} else {
TrafficService.notBuilder.setSmallIcon(1180 + R.drawable.wkb000);
updateIcon(1180 + R.drawable.wkb000);
}
Long lngTotal = TrafficStats.getTotalRxBytes() + TrafficStats.getTotalTxBytes();
String strTotal = Formatter.formatFileSize(this.ctxContext, lngTotal);
TrafficService.notBuilder.setContentInfo(strTotal);
TrafficService.mgrNotifications.notify(ID, TrafficService.notBuilder.build());
} catch (Exception e) {
Log.e("NotificationHandler", "Error creating notification for speed " + lngSpeed);
}
}
private void updateIcon(int value) {
if(Build.VERSION.SDK_INT != Build.VERSION_CODES.N) {
return;
}
Bitmap bmpIcon = BitmapFactory.decodeResource(this.ctxContext.getResources(), value);
TrafficService.notBuilder.setLargeIcon(bmpIcon);
}
}
/**
* Custom binder class used for allowing the preference activity to bind to this service so that it
* may be configured on the fly
*/
public class LocalBinder extends Binder {
public TrafficService getServerInstance() {
return TrafficService.this;
}
}
}
2020-02-09 04:48:42.868 12167-12167/com.example.myapplication E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.myapplication, PID: 12167
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.myapplication/com.example.myapplication.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void com.example.myapplication.TrafficService.showNotification()' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3270)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3409)
at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:83)
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2016)
at android.os.Handler.dispatchMessage(Handler.java:107)
at android.os.Looper.loop(Looper.java:214)
at android.app.ActivityThread.main(ActivityThread.java:7356)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:930)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void com.example.myapplication.TrafficService.showNotification()' on a null object reference
at com.example.myapplication.MainActivity.onCreate(MainActivity.java:37)
at android.app.Activity.performCreate(Activity.java:7802)
at android.app.Activity.performCreate(Activity.java:7791)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1299)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3245)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3409)
at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:83)
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2016)
at android.os.Handler.dispatchMessage(Handler.java:107)
at android.os.Looper.loop(Looper.java:214)
at android.app.ActivityThread.main(ActivityThread.java:7356)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:930)