尝试在空对象引用上调用虚拟方法“android.os.Looper android.content.Context.getMainLooper()" [英] Attempt to invoke virtual method 'android.os.Looper android.content.Context.getMainLooper()' on a null object reference
本文介绍了尝试在空对象引用上调用虚拟方法“android.os.Looper android.content.Context.getMainLooper()"的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！
问题描述
每当我尝试在手机或模拟器上打开应用程序时，我的 Log cat 都会收到此错误.为了让您大致了解我目前正在做的项目，它是一个记录连接到手机接入点的设备数据的系统，可以通过屏幕上的按钮打开和关闭.
我想归功于:
和
Log cat 文件的图像是:https://i.gyazo.com/fa068fd1fce3f27f43185c0cd12568c1p.png我的主要活动课
公共类 MainActivity 扩展 ActionBarActivity{boolean wasApEnabled = false;静态接入点 wifiAP；私人 WifiManager wifi；静态按钮 apButton;静态文本视图文本视图；@覆盖protected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);apButton = (Button) findViewById(R.id.toggleBtn);textView = (TextView) findViewById(R.id.wifiClients);wifiAP = new AccessPoint();wifi = (WifiManager) getSystemService(Context.WIFI_SERVICE);扫描();apButton.setOnClickListener(new View.OnClickListener() {公共无效onClick(查看视图){wifiAP.toggleWifiAP(wifi, MainActivity.this);}});getWindow().addFlags(WindowManager.LayoutParams.FLAG_DISMISS_KEYGUARD|WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON|WindowManager.LayoutParams.FLAG_DIM_BEHIND);}私人无效扫描(){wifiAP.getClientList(false, new FinishScanListener() {@覆盖public void onFinishScan(final ArrayList clients) {textView.setText("WifiApState:" + wifiAP.getWifiApState()+ "\n\n");textView.append("客户:\n");for (ClientScanResult clientScanResult : 客户端){textView.append("======================\n");textView.append("ipAddress:" + clientScanResult.getIpAddress() + "\n");textView.append("设备:" + clientScanResult.getDevice() + "\n");textView.append("macAddress:" + clientScanResult.getMacAddress() + "\n");textView.append("isReachable: "+ clientScanResult.isReachable() + "\n");}}});}@覆盖公共无效 onResume() {super.onResume();如果(wasApEnabled){if (wifiAP.getWifiApState() != wifiAP.WIFI_STATE_ENABLED && wifiAP.getWifiApState() != wifiAP.WIFI_STATE_ENABLING) {wifiAP.toggleWifiAP(wifi, MainActivity.this);}}更新状态显示()；}@覆盖公共无效 onPause() {super.onPause();boolean wifiApIsOn = wifiAP.getWifiApState()==wifiAP.WIFI_STATE_ENABLED ||wifiAP.getWifiApState()==wifiAP.WIFI_STATE_ENABLING;如果(wifiApIsOn){wasApEnabled = true;wifiAP.toggleWifiAP(wifi, MainActivity.this);}别的 {wasApEnabled = false;}更新状态显示()；}public static void updateStatusDisplay(){if (wifiAP.getWifiApState()==wifiAP.WIFI_STATE_ENABLED || wifiAP.getWifiApState()==wifiAP.WIFI_STATE_ENABLED){apButton.setText(关闭");}别的 {apButton.setText(开启");}}@覆盖公共布尔 onCreateOptionsMenu(菜单菜单){menu.add(0,0,0, 获取客户");返回 super.onCreateOptionsMenu(menu);}public boolean onOptionsItemSelected(int featureId, MenuItem item) {开关(item.getItemId()){案例0:扫描();休息;}返回 super.onMenuItemSelected(featureId, item);}} AccessPoint 类
public class AccessPoint extends Activity {私有静态 int 常量 = 0;私有上下文上下文；私有静态 int WIFI_STATE_UNKNOWN = -1;私有静态 int WIFI_STATE_DISABLING = 0;私有静态 int WIFI_STATE_DISABLED = 1;公共静态 int WIFI_STATE_ENABLING = 2;公共静态 int WIFI_STATE_ENABLED = 3;私有静态 int WIFI_STATE_FAILED = 4;最终静态字符串[] WIFI_STATE_TEXTSTATE = 新字符串[]{禁用"、禁用"、启用"、启用"、失败"};私人 WifiManager wifi；private String TAG =WifiAP"；私人 int stateWifi = -1;private boolean alwaysEnabledWifi = true;//开启或关闭wifi公共无效toggleWifiAP(WifiManager wifiHandler，上下文上下文){如果(wifi == null){wifi = wifiHandler;}布尔 wifiApIsOn = getWifiApState() == WIFI_STATE_ENABLED ||getWifiApState()==WIFI_STATE_ENABLING;new SetWifiApTask(!wifiApIsOn, false, context).execute();}私有 int setWifiApEnabled(启用布尔值){Log.d(TAG,设置wifi启用调用"+启用);WifiConfiguration config = new WifiConfiguration();config.SSID =参加讲座"；config.allowedAuthAlgorithms.set(WifiConfiguration.AuthAlgorithm.OPEN);//记住无线状态如果(启用&& stateWifi == -1){stateWifi = wifi.getWifiState();}//关闭无线如果(启用&& wifi.getConnectionInfo() !=null){Log.d(TAG,禁用wifi:呼叫");wifi.setWifiEnabled(false);int loopMax = 10;while (loopMax > 0 && wifi.getWifiState() != WifiManager.WIFI_STATE_DISABLED){Log.d(TAG, 禁用 Wifi:等待，通过:" + (10-loopMax));尝试{线程睡眠(500)；loopMax--;}catch(异常 e){e.printStackTrace();}}Log.d(TAG,"禁用wifi完成，通过:"+(10-loopMax));}//启用和禁用wifi APint state = WIFI_STATE_UNKNOWN;尝试 {Log.d(TAG，(启用?启用":禁用")+wifi ap:调用")；wifi.setWifiEnabled(false);Method method1 = wifi.getClass().getMethod("setWifiApEnabled", WifiConfiguration.class, boolean.class);method1.invoke(wifi, config, enabled);方法 method2 = wifi.getClass().getMethod("getWifiState");state = (Integer)method2.invoke(wifi);}catch(异常 e){//Log.e(WIFI_SERVICE, e.getMessage());}//在处理发生时使用线程如果(！启用){int loopMax = 10;while (loopMax>0 && (getWifiApState()==WIFI_STATE_DISABLING || getWifiApState()==WIFI_STATE_ENABLED || getWifiApState()==WIFI_STATE_FAILED)){Log.d(TAG，(启用?启用":禁用")+wifi AP:等待，通过:"+(10-loopMax))；尝试 {线程睡眠(500)；loopMax--;}catch(异常 e){}}Log.d(TAG，(启用?启用":禁用")+Wifi ap:完成，通过:+(10-loopMax))；//开启无线网络if (stateWifi==WifiManager.WIFI_STATE_ENABLED || stateWifi==WifiManager.WIFI_STATE_ENABLING || stateWifi==WifiManager.WIFI_STATE_UNKNOWN || alwaysEnabledWifi){Log.d(TAG,启用wifi:呼叫");wifi.setWifiEnabled(true);//这种方式它不会阻止事情并等待它被启用}stateWifi = -1;}否则如果(启用){int loopMax = 10;while (loopMax>0 && (getWifiApState()==WIFI_STATE_ENABLING || getWifiApState()==WIFI_STATE_DISABLED || getWifiApState()==WIFI_STATE_FAILED)){Log.d(TAG，(启用?启用":禁用")+wifi ap:等待，通过:"+(10-loopMax))；尝试{线程睡眠(500)；loopMax--;}catch(异常 e){}}Log.d(TAG，(启用?启用":禁用")+wifi ap:完成，通过:"+(10-loopMax))；}返回状态；}//获取wifi AP状态公共 int getWifiApState(){int state = WIFI_STATE_UNKNOWN;尝试 {Method method2 = wifi.getClass().getMethod("getWifiApState");state = (Integer) method2.invoke(wifi);}catch(异常 e){}如果(状态> = 10){常数=10；}WIFI_STATE_DISABLING = 0+常数；WIFI_STATE_DISABLED = 1+常数；WIFI_STATE_ENABLING = 2+常数；WIFI_STATE_ENABLED = 3+常数；WIFI_STATE_FAILED = 4+常数；Log.d(TAG, "getWifiApState " + (state==-1?"UNKNOWN":WIFI_STATE_TEXTSTATE[state-constant]));返回状态；}class SetWifiApTask 扩展了 AsyncTask{布尔 mMode;布尔 mFinish;ProgressDialog pDialog;公共 SetWifiApTask(布尔模式，布尔完成，上下文上下文){mMode = 模式；mFinish = 完成；pDialog = new ProgressDialog(context);}@覆盖protected void onPreExecute(){super.onPreExecute();pDialog.setTitle(打开接入点"+(mMode?开":关"+..."))；pDialog.setMessage("请稍等...");pDialog.show();}@覆盖protected void onPostExecute(Void aVoid){super.onPostExecute(aVoid);尝试 {pDialog.dismiss();MainActivity.updateStatusDisplay();}catch (IllegalArgumentException e){};如果(mFinish){结束();}}@覆盖受保护的 Void doInBackground(Void... params) {setWifiApEnabled(mMode);返回空；}}//获取连接到wifi热点的列表public void getClientList(boolean onlyReachable, FinishScanListener finishListener){getClientList(onlyReachable, 300, finishListener);}public void getClientList(final boolean onlyReachable, final intreachableTimeout, final FinishScanListener finishListener){可运行可运行 = 新可运行(){@覆盖公共无效运行(){BufferedReader br = null;最终的 ArrayList结果 = 新的 ArrayList();尝试 {br = new BufferedReader(new FileReader("/proc/net/arp"));字符串线；while ((line = br.readLine()) != null){String[] splitted = line.split("+");if ((splitted !=null) && (splitted.length >=4)){字符串 mac = 拆分 [3];if (mac.matches("..:..:..:..:..:..")){boolean isReachable = InetAddress.getByName(splitted[0]).isReachable(reachableTimeout);if (!onlyReachable || isReachable){result.add(new ClientScanResult(splitted[0],splitted[3],splitted[5],isReachable));}}}}}catch(异常 e){Log.e(this.getClass().toString(), e.toString());}最后 {尝试 {br.close();}catch (IOException e){Log.e(this.getClass().toString(), e.getMessage());}}//获取将用于发布到主线程的处理程序Handler mainHandler = new Handler(context.getMainLooper());Runnable myRunnable = new Runnable() {@覆盖公共无效运行(){finishListener.onFinishScan(result);}};mainHandler.post(myRunnable);}};线程 myThread = 新线程(可运行)；myThread.start();}} 解决方案
据我所知，你的 Context 是 null.您在类的顶部有一个私有变量 Context，但您从未为其分配任何内容，因此它是 null.
给你的 AccessPoint 一个构造函数并输入类似的东西
context = getContext();里面.
I am getting this error in my Log cat whenever I try to open the application on either my phone or the emulator. To give you an overview of the project that I am currently doing, it is a system that records the data of the devices connected to the access point on the phone which can be toggled on and off via a button on screen.
I want to give credit to:
and
an image of the Log cat file is: https://i.gyazo.com/fa068fd1fce3f27f43185c0cd12568c1.png
my main activity class
public class MainActivity extends ActionBarActivity{
boolean wasApEnabled = false;
static AccessPoint wifiAP;
private WifiManager wifi;
static Button apButton;
static TextView textView;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
apButton = (Button) findViewById(R.id.toggleBtn);
textView = (TextView) findViewById(R.id.wifiClients);
wifiAP = new AccessPoint();
wifi = (WifiManager) getSystemService(Context.WIFI_SERVICE);
scan();
apButton.setOnClickListener(new View.OnClickListener() {
public void onClick(View view) {
wifiAP.toggleWifiAP(wifi, MainActivity.this);
}
});
getWindow().addFlags(WindowManager.LayoutParams.FLAG_DISMISS_KEYGUARD|WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON|WindowManager.LayoutParams.FLAG_DIM_BEHIND);
}
private void scan(){
wifiAP.getClientList(false, new FinishScanListener() {
@Override
public void onFinishScan(final ArrayList<ClientScanResult> clients) {
textView.setText("WifiApState:" + wifiAP.getWifiApState()+ "\n\n");
textView.append("Clients: \n");
for (ClientScanResult clientScanResult : clients){
textView.append("====================\n");
textView.append("ipAddress: " + clientScanResult.getIpAddress() + "\n");
textView.append("Device: " + clientScanResult.getDevice() + "\n");
textView.append("macAddress: " + clientScanResult.getMacAddress() + "\n");
textView.append("isReachable: " + clientScanResult.isReachable() + "\n");
}
}
});
}
@Override
public void onResume() {
super.onResume();
if (wasApEnabled) {
if (wifiAP.getWifiApState() != wifiAP.WIFI_STATE_ENABLED && wifiAP.getWifiApState() != wifiAP.WIFI_STATE_ENABLING) {
wifiAP.toggleWifiAP(wifi, MainActivity.this);
}
}
updateStatusDisplay();
}
@Override
public void onPause() {
super.onPause();
boolean wifiApIsOn = wifiAP.getWifiApState()==wifiAP.WIFI_STATE_ENABLED || wifiAP.getWifiApState()==wifiAP.WIFI_STATE_ENABLING;
if (wifiApIsOn){
wasApEnabled = true;
wifiAP.toggleWifiAP(wifi, MainActivity.this);
}else {
wasApEnabled = false;
}
updateStatusDisplay();
}
public static void updateStatusDisplay(){
if (wifiAP.getWifiApState()==wifiAP.WIFI_STATE_ENABLED || wifiAP.getWifiApState()==wifiAP.WIFI_STATE_ENABLING){
apButton.setText("Turn Off");
}else {
apButton.setText("Turn on");
}
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
menu.add(0,0,0, "Get Clients");
return super.onCreateOptionsMenu(menu);
}
public boolean onOptionsItemSelected(int featureId, MenuItem item) {
switch (item.getItemId()){
case 0:
scan();
break;
}
return super.onMenuItemSelected(featureId, item);
}
}
AccessPoint class
public class AccessPoint extends Activity {
private static int constant = 0;
private Context context;
private static int WIFI_STATE_UNKNOWN = -1;
private static int WIFI_STATE_DISABLING = 0;
private static int WIFI_STATE_DISABLED = 1;
public static int WIFI_STATE_ENABLING = 2;
public static int WIFI_STATE_ENABLED = 3;
private static int WIFI_STATE_FAILED = 4;
final static String[] WIFI_STATE_TEXTSTATE = new String[]{
"DISABLING","DISABLED","ENABLING","ENABLED","FAILED"
};
private WifiManager wifi;
private String TAG = "WifiAP";
private int stateWifi = -1;
private boolean alwaysEnabledWifi = true;
//enable or disable the wifi
public void toggleWifiAP(WifiManager wifiHandler, Context context){
if (wifi == null){
wifi = wifiHandler;
}
boolean wifiApIsOn = getWifiApState() == WIFI_STATE_ENABLED || getWifiApState()==WIFI_STATE_ENABLING;
new SetWifiApTask(!wifiApIsOn, false, context).execute();
}
private int setWifiApEnabled(boolean enabled){
Log.d(TAG, "Set wifi enabled called" + enabled);
WifiConfiguration config = new WifiConfiguration();
config.SSID = "Attend Lecture";
config.allowedAuthAlgorithms.set(WifiConfiguration.AuthAlgorithm.OPEN);
//remember wireless state
if (enabled && stateWifi == -1){
stateWifi = wifi.getWifiState();
}
//disable the wireless
if (enabled && wifi.getConnectionInfo() !=null){
Log.d(TAG, "disable wifi: calling");
wifi.setWifiEnabled(false);
int loopMax = 10;
while (loopMax > 0 && wifi.getWifiState() != WifiManager.WIFI_STATE_DISABLED){
Log.d(TAG, "Disable Wifi: Waiting, pass:" + (10-loopMax));
try{
Thread.sleep(500);
loopMax--;
}catch (Exception e){
e.printStackTrace();
}
}
Log.d(TAG, "Disabling wifi is done, pass: " + (10-loopMax));
}
//enable and disable wifi AP
int state = WIFI_STATE_UNKNOWN;
try {
Log.d(TAG, (enabled?"enabling":"Disabling")+"wifi ap: calling");
wifi.setWifiEnabled(false);
Method method1 = wifi.getClass().getMethod("setWifiApEnabled", WifiConfiguration.class, boolean.class);
method1.invoke(wifi, config, enabled);
Method method2 = wifi.getClass().getMethod("getWifiState");
state = (Integer)method2.invoke(wifi);
}catch (Exception e){
//Log.e(WIFI_SERVICE, e.getMessage());
}
//Use thread while processing occurs
if (!enabled){
int loopMax = 10;
while (loopMax>0 && (getWifiApState()==WIFI_STATE_DISABLING || getWifiApState()==WIFI_STATE_ENABLED || getWifiApState()==WIFI_STATE_FAILED)){
Log.d(TAG, (enabled?"enabling": "disabling")+ "wifi AP: waiting, pass:" + (10-loopMax));
try {
Thread.sleep(500);
loopMax--;
}catch (Exception e){
}
}
Log.d(TAG, (enabled?"enabling":"disabling")+" Wifi ap: done, pass: " + (10-loopMax));
//enable the wifi
if (stateWifi==WifiManager.WIFI_STATE_ENABLED || stateWifi==WifiManager.WIFI_STATE_ENABLING || stateWifi==WifiManager.WIFI_STATE_UNKNOWN || alwaysEnabledWifi){
Log.d(TAG, "enable wifi: Calling");
wifi.setWifiEnabled(true);
//this way it doesnt hold things up and waits for it to get enabled
}
stateWifi = -1;
}else if (enabled){
int loopMax = 10;
while (loopMax>0 && (getWifiApState()==WIFI_STATE_ENABLING || getWifiApState()==WIFI_STATE_DISABLED || getWifiApState()==WIFI_STATE_FAILED)){
Log.d(TAG, (enabled?"Enabling": "disabling") + "wifi ap: waiting, pass: " + (10-loopMax));
try{
Thread.sleep(500);
loopMax--;
}catch (Exception e){
}
}
Log.d(TAG, (enabled?"Enabling": "disabling")+ "wifi ap: done, pass: " + (10-loopMax));
}
return state;
}
//Get the wifi AP state
public int getWifiApState(){
int state = WIFI_STATE_UNKNOWN;
try {
Method method2 = wifi.getClass().getMethod("getWifiApState");
state = (Integer) method2.invoke(wifi);
}catch (Exception e){
}
if (state>=10){
constant=10;
}
WIFI_STATE_DISABLING = 0+constant;
WIFI_STATE_DISABLED = 1+constant;
WIFI_STATE_ENABLING = 2+constant;
WIFI_STATE_ENABLED = 3+constant;
WIFI_STATE_FAILED = 4+constant;
Log.d(TAG, "getWifiApState " + (state==-1?"UNKNOWN":WIFI_STATE_TEXTSTATE[state-constant]));
return state;
}
class SetWifiApTask extends AsyncTask<Void, Void, Void>{
boolean mMode;
boolean mFinish;
ProgressDialog pDialog;
public SetWifiApTask(boolean mode, boolean finish, Context context){
mMode = mode;
mFinish = finish;
pDialog = new ProgressDialog(context);
}
@Override
protected void onPreExecute(){
super.onPreExecute();
pDialog.setTitle("Turning on Access Point " + (mMode?"On":"Off" + "..."));
pDialog.setMessage("Please wait a moment...");
pDialog.show();
}
@Override
protected void onPostExecute(Void aVoid){
super.onPostExecute(aVoid);
try {
pDialog.dismiss();
MainActivity.updateStatusDisplay();
}catch (IllegalArgumentException e){
};
if (mFinish){
finish();
}
}
@Override
protected Void doInBackground(Void... params) {
setWifiApEnabled(mMode);
return null;
}
}
//get the list connected to the wifi hotspot
public void getClientList(boolean onlyReachable, FinishScanListener finishListener){
getClientList(onlyReachable, 300, finishListener);
}
public void getClientList(final boolean onlyReachable, final int reachableTimeout, final FinishScanListener finishListener){
Runnable runnable = new Runnable() {
@Override
public void run() {
BufferedReader br = null;
final ArrayList<ClientScanResult> result = new ArrayList<>();
try {
br = new BufferedReader(new FileReader("/proc/net/arp"));
String line;
while ((line = br.readLine()) != null){
String[] splitted = line.split(" +");
if ((splitted !=null) && (splitted.length >=4)){
String mac = splitted[3];
if (mac.matches("..:..:..:..:..:..")){
boolean isReachable = InetAddress.getByName(splitted[0]).isReachable(reachableTimeout);
if (!onlyReachable || isReachable){
result.add(new ClientScanResult(splitted[0], splitted[3], splitted[5], isReachable));
}
}
}
}
}catch (Exception e){
Log.e(this.getClass().toString(), e.toString());
}finally {
try {
br.close();
}catch (IOException e){
Log.e(this.getClass().toString(), e.getMessage());
}
}
//Get handler that will be used to post to main thread
Handler mainHandler = new Handler(context.getMainLooper());
Runnable myRunnable = new Runnable() {
@Override
public void run() {
finishListener.onFinishScan(result);
}
};
mainHandler.post(myRunnable);
}
};
Thread myThread = new Thread(runnable);
myThread.start();
}
}
解决方案
As far as I can see it, your Context is null. You have a private variable Context at the top of your class, but you never assign anything to it, so it's null.
Give your AccessPoint a constructor and put something like
context = getContext();
inside of it.
这篇关于尝试在空对象引用上调用虚拟方法“android.os.Looper android.content.Context.getMainLooper()"的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
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