如何检查TCP套接字是否在Android应用程序中连接 [英] How to check if TCP socket is connected in android app
问题描述
我在写一个简短的测试应用程序来练习连接到服务器。所有的应用程序都是从editText框中获取一个IP，然后连接到服务器。看起来我可以连接到服务器，因为我可以发送数据到服务器，并让服务器打印它。
I'm writing a short test app to practice connecting to a server. All the app does is take an IP from an editText box, and then connect to the server. It looks like I can connect to the server because I am able to send data to the server and have the server print it.
我想添加一些错误检查确认我尝试发送任何东西到服务器之前连接。然而，问题是，每当我使用Socket.isConnected（）或isBound（）方法我的应用程序崩溃。
I wanted to add some error checking to confirm that I am connected before attempting to send anything to the server. However, the problem is, whenever I use the Socket.isConnected() or isBound() methods my app crashes.
那么如何检查如果我连接if这些方法似乎不工作。正如我所说，我知道我已连接，因为我可以发送东西到服务器。
So how do I check if I'm connected if these methods doesn't seem to work. As I said, I know I'm connected because I can send stuff to the server.
下面是代码，我按下按钮连接。我想做的是确认我已连接，然后启动一个线程，将工作在后台发送和接收来自服务器的数据。在说s.isBound（）的部分，程序崩溃。我甚至可以放在s.isConnected（），它也会崩溃。
Below is the code, I connect on the press of a button. What I want to do is confirm that I'm connected, and then kick off a thread that will work in the background sending and receiving data from the server. In the section that say's s.isBound() is where the program crashes. I can even put in s.isConnected() and it will crash also.
最后，isBound和isConnected有什么区别？
Last, what is the difference between isBound, and isConnected?
private OnClickListener connectListener = new OnClickListener() {
@Override
public void onClick(View v) {
if (!connected) {
serverIpAddress = serverIp.getText().toString();
if (!serverIpAddress.equals("")) {
try{
InetAddress serverAddr = InetAddress.getByName(serverIpAddress);
Log.d("ClientActivity", "Trying to Connect");
s = new Socket(serverAddr, SERVERPORT);
Log.d("ClientActivity", "Connected");
output = s.getOutputStream();
input = s.getInputStream();
}
catch (UnknownHostException e) {
e.printStackTrace();
}
catch (IOException e) {
e.printStackTrace();
}
if(s.isBound()){
connected = true;
cThread = new Thread(new ClientThread());
cThread.setName("Client Connection Thread");
cThread.start();
}
}
}
}
};
这是日志输出的内容。
11-13 17:03:56.718: D/ClientActivity(2039): Trying to Connect
11-13 17:03:56.757: W/System.err(2039): java.net.ConnectException: /192.168.16.1:6340 - Connection refused
11-13 17:03:56.757: W/System.err(2039): at org.apache.harmony.luni.net.PlainSocketImpl.connect(PlainSocketImpl.java:207)
11-13 17:03:56.757: W/System.err(2039): at org.apache.harmony.luni.net.PlainSocketImpl.connect(PlainSocketImpl.java:183)
11-13 17:03:56.757: W/System.err(2039): at java.net.Socket.startupSocket(Socket.java:705)
11-13 17:03:56.757: W/System.err(2039): at java.net.Socket.<init>(Socket.java:263)
11-13 17:03:56.757: W/System.err(2039): at com.AUIEE.client_test.Client_TestActivity$1.onClick(Client_TestActivity.java:88)
11-13 17:03:56.757: W/System.err(2039): at android.view.View.performClick(View.java:2485)
11-13 17:03:56.765: W/System.err(2039): at android.view.View$PerformClick.run(View.java:9089)
11-13 17:03:56.765: W/System.err(2039): at android.os.Handler.handleCallback(Handler.java:587)
11-13 17:03:56.765: W/System.err(2039): at android.os.Handler.dispatchMessage(Handler.java:92)
11-13 17:03:56.773: W/System.err(2039): at android.os.Looper.loop(Looper.java:130)
11-13 17:03:56.773: W/System.err(2039): at android.app.ActivityThread.main(ActivityThread.java:3859)
11-13 17:03:56.773: W/System.err(2039): at java.lang.reflect.Method.invokeNative(Native Method)
11-13 17:03:56.773: W/System.err(2039): at java.lang.reflect.Method.invoke(Method.java:507)
11-13 17:03:56.773: W/System.err(2039): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:840)
11-13 17:03:56.773: W/System.err(2039): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:598)
11-13 17:03:56.773: W/System.err(2039): at dalvik.system.NativeStart.main(Native Method)
11-13 17:03:56.781: D/AndroidRuntime(2039): Shutting down VM
11-13 17:03:56.781: W/dalvikvm(2039): threadid=1: thread exiting with uncaught exception (group=0x4001e560)
11-13 17:03:56.789: E/AndroidRuntime(2039): FATAL EXCEPTION: main
11-13 17:03:56.789: E/AndroidRuntime(2039): java.lang.NullPointerException
11-13 17:03:56.789: E/AndroidRuntime(2039): at com.AUIEE.client_test.Client_TestActivity$1.onClick(Client_TestActivity.java:103)
11-13 17:03:56.789: E/AndroidRuntime(2039): at android.view.View.performClick(View.java:2485)
11-13 17:03:56.789: E/AndroidRuntime(2039): at android.view.View$PerformClick.run(View.java:9089)
11-13 17:03:56.789: E/AndroidRuntime(2039): at android.os.Handler.handleCallback(Handler.java:587)
11-13 17:03:56.789: E/AndroidRuntime(2039): at android.os.Handler.dispatchMessage(Handler.java:92)
11-13 17:03:56.789: E/AndroidRuntime(2039): at android.os.Looper.loop(Looper.java:130)
11-13 17:03:56.789: E/AndroidRuntime(2039): at android.app.ActivityThread.main(ActivityThread.java:3859)
11-13 17:03:56.789: E/AndroidRuntime(2039): at java.lang.reflect.Method.invokeNative(Native Method)
11-13 17:03:56.789: E/AndroidRuntime(2039): at java.lang.reflect.Method.invoke(Method.java:507)
11-13 17:03:56.789: E/AndroidRuntime(2039): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:840)
11-13 17:03:56.789: E/AndroidRuntime(2039): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:598)
11-13 17:03:56.789: E/AndroidRuntime(2039): at dalvik.system.NativeStart.main(Native Method)
推荐答案
首先，
if(s.isBound()){
connected = true;
cThread = new Thread(new ClientThread());
cThread.setName("Client Connection Thread");
cThread.start();
}
如果任何catch块被触发，那么它将执行上面的块。但是，如果引发异常意味着 s 可能为null，因此您有一个特定的NullPointerException。 （应用程序崩溃）适当的位置在 try 块内。
block is at a wrong place. If any catch block triggered, then it will execute the above block. But if an exception is raised that means that s will probably be null, so you have a certain NullPointerException. (crash of the application) The appropriate place is inside the try block.
其次， logcat日志，您尝试建立的连接拒绝。可能是ip / port或防火墙有问题。
Secondly, as you can see from the logcat log, the connection that you are trying to establish refuses. Perhaps there is something wrong with the ip/port or a firewall.
还有logcat通知你可能有未捕获的异常。
Also logcat informs you that you probably have an uncaught exception.
1-13 17:03:56.781: W/dalvikvm(2039): threadid=1: thread exiting with uncaught exception (group=0x4001e560)
修复问题，如果问题仍然存在，请再次讨论。
Fix that problems and if the problem persist come again to discuss it.
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