Question

我是android编程新手，我试图通过Android上的TCP客户端接收数据包数据。

我从raspberry pi获取流数据包后，数据包将被解析为变量，在我的Masukan（）函数中返回字符串值 filter 。

我可以在Adhrs Activity上获得Masukan（）的返回值，但是我无法从另一个活动中获取Masukan（）的返回值。

错误说Nullpointerexception，我将不胜感激任何帮助。这是我的代码：

 package com.uavgama;
 import java.io.BufferedReader;
 import java.io.IOException;
 import java.io.InputStreamReader;
 import java.net.Socket;
 import java.net.UnknownHostException;
 import android.app.Activity;
 import android.content.Intent;
 import android.os.Bundle;
 import android.os.Handler;
 import android.widget.TextView;
 public class Adhrsparse extends Activity {
 String[] parsing = null;
 private final String server = "192.168.43.20";

 Handler handler = new Handler();
 Runnable runnable = new Runnable() {
 public void run() {
 Keluar();

 }
 };

 //declaration of textview etc

 @Override
 public void onCreate(Bundle savedInstanceState) {
 super.onCreate(savedInstanceState);
 setContentView(R.layout.adahrs);
 status = (TextView) findViewById(R.id.textView16);
 paketdata = (TextView) findViewById(R.id.textView17);

 tvalt = (TextView) findViewById(R.id.textView18);
 tvasp = (TextView) findViewById(R.id.textView19);
 tvlat = (TextView) findViewById(R.id.textView20);
 tvlon = (TextView) findViewById(R.id.textView21);
 tvptc = (TextView) findViewById(R.id.textView22);
 tvrol = (TextView) findViewById(R.id.textView23);
 tvyaw = (TextView) findViewById(R.id.textView24);

 Keluar();

 }

 public String Keluar(){

  String masuk = new String();
  try {
  masuk = Masukan();
  status.setText(masuk);
  } catch (UnknownHostException e) {
  // TODO Auto-generated catch block
  e.printStackTrace();
  } catch (IOException e) {
  // TODO Auto-generated catch block
  //    Intent intentcam = new Intent(this,CameraView.class);
  //    intentcam.putExtra("filter", filter);
  //    startActivity(intentcam);
  e.printStackTrace();
  }

  handler.postDelayed(runnable, 100);
  return masuk;
  }

  public String Masukan() throws UnknownHostException, IOException{

  Socket s = new Socket(server,12345);
  //BufferedReader inp = null;
  BufferedReader inp = new BufferedReader(new InputStreamReader(s.getInputStream()));
  //String serverMsg = null;
  String serverMsg = inp.readLine();
  //filter keutuhan data kemudian diprint di var paketdata
  if ( serverMsg.endsWith("#")) {
  filter = serverMsg; 
  }
  paketdata.setText(filter);
  parsing = filter.split("\\|");

  parsing[0] = parsing[0].replace("$", "");
  tvalt.setText(parsing[0]);
  tvasp.setText(parsing[1]);
  tvlat.setText(parsing[2]);
  tvlon.setText(parsing[3]);
  tvptc.setText(parsing[4]);
  tvrol.setText(parsing[5]);
  parsing[6] = parsing[6].replace("#", "");
  tvyaw.setText(parsing[6]);

  s.close();

return filter; 

  };

  }

和我的另一项活动

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.Socket;
import java.net.UnknownHostException;
import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.os.Handler;
import android.widget.TextView;
import com.uavgama.Adhrsparse;

public class CameraView extends Activity{
String[] parsingcam = null;
private final String server = "192.168.43.20";
InetAddress


   /** Called when the activity is first created. */
Scanner scanner = new Scanner(System.in);
Handler handler = new Handler();
Runnable runnable = new Runnable() 
{
    public void run() {
        adhrspars();

 }
  };

TextView statuse;
TextView paketdata;
TextView data;
String latlon;
String filter;
String parse;



@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.camera);
      runnable.run();
    Intent fltr = getIntent();
    latlon = fltr.getStringExtra("filter");
    data.setText(latlon);


    adhrspars();
          adhrs();


}


public void adhrspars(){
adhrs();


}

public void adhrs() {
String parsed = new String();
    Adhrsparse adhrs = new Adhrsparse();
    try {
        parsed = adhrs.Masukan() ;
        data.setText(parsed);
    } catch (UnknownHostException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }

    handler.postDelayed(runnable, 100);


    };

这是我的logcat：

 07-23 20:00:14.708: E/AndroidRuntime(24895): FATAL EXCEPTION: main
 07-23 20:00:14.708: E/AndroidRuntime(24895): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.uavgama/com.uavgama.CameraView}:      java.lang.NullPointerException
 07-23 20:00:14.708: E/AndroidRuntime(24895):   at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2063)
 07-23 20:00:14.708: E/AndroidRuntime(24895):   at android.app.ActivityThread.startActivityNow(ActivityThread.java:1904)
 07-23 20:00:14.708: E/AndroidRuntime(24895):   at android.app.LocalActivityManager.moveToState(LocalActivityManager.java:135)
 07-23 20:00:14.708: E/AndroidRuntime(24895):   at android.app.LocalActivityManager.startActivity(LocalActivityManager.java:347)
 07-23 20:00:14.708: E/AndroidRuntime(24895):   at android.widget.TabHost$IntentContentStrategy.getContentView(TabHost.java:753)
 07-23 20:00:14.708: E/AndroidRuntime(24895):   at android.widget.TabHost.setCurrentTab(TabHost.java:417)
 07-23 20:00:14.708: E/AndroidRuntime(24895):   at android.widget.TabHost$2.onTabSelectionChanged(TabHost.java:158)
 07-23 20:00:14.708: E/AndroidRuntime(24895):   at android.widget.TabWidget$TabClickListener.onClick(TabWidget.java:546)
 07-23 20:00:14.708: E/AndroidRuntime(24895):   at android.view.View.performClick(View.java:4103)
 07-23 20:00:14.708: E/AndroidRuntime(24895):   at android.view.View$PerformClick.run(View.java:17117)
 07-23 20:00:14.708: E/AndroidRuntime(24895):   at android.os.Handler.handleCallback(Handler.java:615)
 07-23 20:00:14.708: E/AndroidRuntime(24895):   at android.os.Handler.dispatchMessage(Handler.java:92)
 07-23 20:00:14.708: E/AndroidRuntime(24895):   at android.os.Looper.loop(Looper.java:137)
 07-23 20:00:14.708: E/AndroidRuntime(24895):   at android.app.ActivityThread.main(ActivityThread.java:4744)
 07-23 20:00:14.708: E/AndroidRuntime(24895):   at java.lang.reflect.Method.invokeNative(Native Method)
 07-23 20:00:14.708: E/AndroidRuntime(24895):   at java.lang.reflect.Method.invoke(Method.java:511)
 07-23 20:00:14.708: E/AndroidRuntime(24895):   at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
 07-23 20:00:14.708: E/AndroidRuntime(24895):   at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
 07-23 20:00:14.708: E/AndroidRuntime(24895):   at dalvik.system.NativeStart.main(Native Method)
 07-23 20:00:14.708: E/AndroidRuntime(24895): Caused by: java.lang.NullPointerException
 07-23 20:00:14.708: E/AndroidRuntime(24895):   at com.uavgama.CameraView.onCreate(CameraView.java:48)
 07-23 20:00:14.708: E/AndroidRuntime(24895):   at android.app.Activity.performCreate(Activity.java:5008)
 07-23 20:00:14.708: E/AndroidRuntime(24895):   at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1079)
 07-23 20:00:14.708: E/AndroidRuntime(24895):   at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2027)
 07-23 20:00:14.708: E/AndroidRuntime(24895):   ... 18 more

感谢您的帮助

Answer 1

我看到了几个问题。首先，如果您没有通过Intent发送数据

 Intent intent = new Intent(FirstActivity.this, SecondActivity.class);
 intent.putExtra("key", value);   // this line here adds the extra data

然后latlon将是null，但不一定会抛出NPE。

其次，我相信这是您获取NPE的地方，您从未初始化TextView data，因此当您尝试拨打NPE时，您会收到setText()它。将您的onCreate()更改为

    @Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.camera);
      runnable.run();
    Intent fltr = getIntent();
    latlon = fltr.getStringExtra("filter");

    data = (TextView) findViewById(R.id.idOfTextView);   // YOU NEED TO INITAILIZE IT LIKE THIS

    data.setText(latlon);

由于您的Masukan()方法在多个地方使用，您可能需要取出获取数据的部分并将它们放在单独的Java类中的static方法中，然后在需要时String只需运行

   String variableName = SomeClassName.Masukan();

来自哪里

将try catch的返回值传递给另一个活动

1 个答案: