嘿伙计们，每当我尝试在手机或模拟器上打开应用程序时，我都会在我的Log cat中收到此错误。为了概述我目前正在进行的项目，它是一个记录连接到手机上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。
我想赞扬：
1）Android 2.3 wifi hotspot API
和
2）https://www.whitebyte.info/android/android-wifi-hotspot-manager-class
Log cat文件的图像是： https://i.gyazo.com/fa068fd1fce3f27f43185c0cd12568c1.png
我的主要活动课
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类
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();
}
}
答案 0 :(得分：3)
据我所见，您的Context为null。您的班级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一个构造函数并添加类似
context = getContext();
里面。