Question

我无法从Android获得Java桌面服务器的价值。我只得到一个输出。我做了循环运行它5次。它运行一次并在android上输出一次然后崩溃。它应该给android输出5次。在每次输出之后，它应该将值传递给java桌面服务器。

我正在做什么以及我想要的是什么：我正在获得信号强度。我想要5个样本。所以我运行代码5次。只要我获得一次该值，我就会将其传递给Java Desktop Server代码。我已经用java编写了server.java，它运行得非常好。

客户代码：

public class MainActivity extends Activity {  
        protected static final long TIME_DELAY = 1000;
        TextView mTextView;
        private WifiManager wifiManager;
        Handler handler=new Handler();  
        int count =0; String data ="";

        private String messsage;

        private static final IntentFilter FILTER = new IntentFilter(
                WifiManager.SCAN_RESULTS_AVAILABLE_ACTION);

        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_main);
            mTextView = (TextView) findViewById(R.id.text_id);          
            wifiManager = (WifiManager) getSystemService(WIFI_SERVICE);         
            wifiManager.startScan();

        }


        @Override
        public void onStart() {
            super.onStart();
            // Register the scan receiver
            registerReceiver(scanReceiver, FILTER);
        }

        @Override
        public void onStop() {
            super.onStop();
            // Unregister the receiver
            unregisterReceiver(scanReceiver);
        }

        public void onClickRefresh(View v) {
            count=0;
            wifiManager.startScan();

            //Log.d(TAG, "onClickRefresh");
        }


        BroadcastReceiver scanReceiver = new BroadcastReceiver() {
            @Override
            public void onReceive(Context context, Intent intent) {
            //  Log.d(TAG, "scanReceiver received!");
                // Refreshes the chart once we have scan results

                // Request a scan again

                if(count<5){
                 final StringBuilder sb = new StringBuilder();

                 List<ScanResult> wifiScanList = wifiManager.getScanResults();
                 for (ScanResult result : wifiScanList) {
                        if (result.SSID.equals("Khosla ka Ghosla")) {
                            sb.append(""+result.level);
                        }
                        if (result.SSID.equals("panny")) {
                            sb.append(""+result.level);
                        }
                        if (result.SSID.equals("ferbora")) {
                            sb.append(""+result.level);
                        }   

                  //      mTextView.setText("getting called " +count + sb);                   
                        messsage=sb.toString();
                        mTextView.setText(messsage);

                    } count++;
                    new Asynctask1().execute(messsage);
                wifiManager.startScan();
                }
            }
        };

          public class Asynctask1 extends AsyncTask<String, Void, Void> {
              private PrintWriter printwriter;
            private static final String IP_ADDRESS = "192.168.0.8";  
            private static final int DEST_PORT = 4444;
            private EditText mTextField;
            protected Void doInBackground(String... messages) {
                String message = messages[0];
                Socket client = null;
                try {
                    client = new Socket(IP_ADDRESS, DEST_PORT); // connect to server
                } catch (UnknownHostException e) {
                    e.printStackTrace();
                } catch (IOException e) {
                    e.printStackTrace();
                }
                // Write to server.
                try {
                    printwriter = new PrintWriter(client.getOutputStream(), true);
                    printwriter.write(messsage); // write the message to output stream
                    printwriter.flush();
                    printwriter.close();
                }
                catch (IOException e) {
                    e.printStackTrace();
                } finally {
                    try {
                        client.close();
                    } catch (IOException e) {
                        e.printStackTrace();
                    }
                }
                return null;
            }
        }
}

我得到的错误是nullpointer异常。我不知道为什么它有空。它给出了错误：finally {try {client.close（）;.

除此之外，log cat没有显示太多东西。你能指导我吗？

Answer 1

你在doInBackground方法中返回null。

错误：空指针异常

1 个答案: