android - 当我开始一个新线程时，我会强制关闭!

Question

我在 android 中有一个应用程序，它类似于客户端服务器应用程序，在我的程序中的某个时刻，我启动了一个新线程，用于将客户端连接到服务器。

我的问题是，当我开始这个新线程时，我不知道会发生什么，但是当我尝试与我的 GUI 交互时(按下一个按钮将我带到另一个 Activity )，我会强制关闭。

这有点令人困惑，因为我在不同的网页上阅读时，我开始的新线程与我的 GUI 没有任何关系，所以即使客户端尝试连接或失败，我也应该能够“玩”我的界面。

这是我的代码:

public class screen1 extends Activity {

private TextView clientState;
private String serverIpAddress="10.0.2.2";
public static final int ClientPort = 8080;
String message="Hello Server!";
int longitude;
int latitude;
private PrintWriter out=null;
DBAdapter db;
private Handler handler=new Handler();
Socket socket;
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.screen1);
    clientState = (TextView) findViewById(R.id.client_Status);

//这是让我进入另一个 Activity 的按钮，当按下它时，它会给我 FC

    Button b = (Button)findViewById(R.id.mainMenu);
    b.setOnClickListener(new View.OnClickListener() {
       public void onClick(View arg0) {
       Intent i = new Intent(screen1.this, screen2.class);
       startActivity(i);
       } 
    });

//这里我开始一个下面定义的新线程

  Thread cThread=new Thread(new ClientThread()); 

  cThread.start();  
db=new DBAdapter(this);

}

//这是我的客户端尝试连接

public class ClientThread implements Runnable{


    public void run()
    {
        try
        {
            InetAddress serverAddr=InetAddress.getByName(serverIpAddress);
            handler.post(new Runnable(){
                public void run(){
                    clientState.setText(" try to connect!");
                }
            });
            socket=new Socket(serverAddr,ClientPort);

            //connected=true;
        handler.post(new Runnable(){
                public void run(){
                    clientState.setText("Connected!");
                }
            });

        PrintWriter out=new PrintWriter(socket.getOutputStream(),true);
        db.createDatabase();
         db.openDataBase();
           Cursor c=db.getAllData();

           if(c.moveToFirst()) 
             {
              do{

                  longitude=Integer.parseInt(c.getString(1));
                  out.println(longitude);
                  latitude=Integer.parseInt(c.getString(2));
                  out.println(latitude);

              }while(c.moveToNext());

             }




        }
        catch(Exception e){
            handler.post(new Runnable(){
                public void run(){
                    clientState.setText("Error");
                    }
            });

            e.printStackTrace();
        }

    }

}

和 onStop() 方法:

protected void onStop() {

 super.onStop();

  try {

        out.close();
        socket.close();

     } catch (IOException e) {
         e.printStackTrace();
     }
 }
}

好吧，就是这样，更多细节我在这里解释。提前谢谢你:)

0

4-16 03:51:25.045: ERROR/AndroidRuntime(242): Uncaught handler: thread main exiting due to uncaught exception

04-16 03:51:25.074: ERROR/AndroidRuntime(242): java.lang.RuntimeException: Unable to stop activity {test.android/test.android.screen1}: java.lang.NullPointerException

04-16 03:51:25.074: ERROR/AndroidRuntime(242):     at android.app.ActivityThread.performStopActivityInner(ActivityThread.java:3227)

04-16 03:51:25.074: ERROR/AndroidRuntime(242):     at android.app.ActivityThread.handleStopActivity(ActivityThread.java:3272)

04-16 03:51:25.074: ERROR/AndroidRuntime(242):     at android.app.ActivityThread.access$2500(ActivityThread.java:119)

04-16 03:51:25.074: ERROR/AndroidRuntime(242):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1880)

04-16 03:51:25.074: ERROR/AndroidRuntime(242):     at android.os.Handler.dispatchMessage(Handler.java:99)

04-16 03:51:25.074: ERROR/AndroidRuntime(242):     at android.os.Looper.loop(Looper.java:123)

04-16 03:51:25.074: ERROR/AndroidRuntime(242):     at android.app.ActivityThread.main(ActivityThread.java:4363)

04-16 03:51:25.074: ERROR/AndroidRuntime(242):     at java.lang.reflect.Method.invokeNative(Native Method)

04-16 03:51:25.074: ERROR/AndroidRuntime(242):     at java.lang.reflect.Method.invoke(Method.java:521)

04-16 03:51:25.074: ERROR/AndroidRuntime(242):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:860)

04-16 03:51:25.074: ERROR/AndroidRuntime(242):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:618)

04-16 03:51:25.074: ERROR/AndroidRuntime(242):     at dalvik.system.NativeStart.main(Native Method)

04-16 03:51:25.074: ERROR/AndroidRuntime(242): Caused by: java.lang.NullPointerException

04-16 03:51:25.074: ERROR/AndroidRuntime(242):     at 
test.android.screen1.onStop(screen1.java:106)

04-16 03:51:25.074: ERROR/AndroidRuntime(242):     at 
android.app.Instrumentation.callActivityOnStop(Instrumentation.java:1169)

04-16 03:51:25.074: ERROR/AndroidRuntime(242):     at android.app.Activity.performStop(Activity.java:3797)

04-16 03:51:25.074: ERROR/AndroidRuntime(242):     at android.app.ActivityThread.performStopActivityInner(ActivityThread.java:3224)

04-16 03:51:25.074: ERROR/AndroidRuntime(242):     ... 11 more

04-16 03:51:25.144: INFO/Process(51): Sending signal. PID: 242 SIG: 3

04-16 03:51:25.154: INFO/dalvikvm(242): threadid=7: reacting to signal 3

04-16 03:51:25.204: INFO/dalvikvm(242): Wrote stack trace to '/data/anr/traces.txt'

04-16 03:51:41.604: INFO/Process(242): Sending signal. PID: 242 SIG: 9

04-16 03:51:41.714: INFO/ActivityManager(51): Process test.android (pid 242) has died.

04-16 03:51:41.753: INFO/WindowManager(51): WIN DEATH: Window{43e0eb10 test.android/test.android.screen2 paused=false}

04-16 03:51:41.765: INFO/WindowManager(51): WIN DEATH: Window{43e068b0 test.android/test.android.screen1 paused=false}

04-16 03:51:41.974: INFO/ActivityManager(51): Start proc test.android for activity test.android/.screen1: pid=249 uid=10030 gids={3003}

04-16 03:51:42.433: DEBUG/ddm-heap(249): Got feature list request

04-16 03:51:42.704: INFO/UsageStats(51): Unexpected resume of test.android while already resumed in test.android

04-16 03:51:43.294: WARN/InputManagerService(51): Got RemoteException sending setActive(false) notification to pid 242 uid 10030

04-16 03:51:43.513: INFO/ActivityManager(51): Displayed activity test.android/.screen1: 1736 ms (total 1736 ms)

好吧，亲爱的 friend 们，我已经从我的代码中删除了 onStop() 函数，一切似乎都正常工作了!

protected void onStop() {

    super.onStop();

    try {

        out.close();


        socket.close();

     } catch (IOException e) {

         e.printStackTrace();

     }
}

它有什么问题？:-S

Answer 1

我假设线程的onStop 方法中的变量out 为null。您声明了该变量，但您使用 null 对其进行了初始化，并且永远不会为其初始化另一个值。

你会

PrintWriter out=new PrintWriter(socket.getOutputStream(),true);

在线程的 run 方法中，但此变量的作用域与 onStop 方法中使用的变量不同。这就是您得到 NullPointerException 的原因。