我尝试使用ListView
与服务器通信后,我的应用停止了。
我的布局:
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
android:paddingBottom="@dimen/activity_vertical_margin"
tools:context="com.ghhwer.pcremote.Main$PlaceholderFragment"
android:id="@+id/Layout">
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Refresh"
android:id="@+id/Refresh"
android:layout_alignParentBottom="true"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true" />
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Connect"
android:id="@+id/Connect"
android:layout_alignTop="@+id/Refresh"
android:layout_toLeftOf="@+id/Disconnect" />
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Disconnect"
android:id="@+id/Disconnect"
android:layout_alignTop="@+id/Connect"
android:layout_alignParentRight="true"
android:layout_alignParentEnd="true" />
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Please make sure you are connected to the same WiFi as your host computer"
android:id="@+id/Text"
android:textSize="15dp"
android:layout_alignParentTop="true"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true" />
<LinearLayout
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true"
android:layout_below="@+id/Text"
android:layout_above="@+id/Refresh">
<ListView
android:id="@+id/ComputerList"
android:layout_width="match_parent"
android:layout_height="wrap_content" >
</ListView>
</LinearLayout>
</RelativeLayout>
Main.java:
import android.app.Activity;
import android.app.Fragment;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.ListView;
import java.io.IOException;
import java.net.UnknownHostException;
import java.util.ArrayList;
public class Main extends Activity {
private ListView lvItem;
private Button btnRefresh;
private ArrayList<String> itemArrey;
private ArrayAdapter<String> itemAdapter;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
setUpView();
if (savedInstanceState == null) {
getFragmentManager().beginTransaction()
.add(R.id.container, new PlaceholderFragment())
.commit();
}
}
private void setUpView() {
btnRefresh = (Button)this.findViewById(R.id.Refresh);
lvItem = (ListView)this.findViewById(R.id.ComputerList);
itemArrey = new ArrayList<String>();
itemArrey.clear();
itemAdapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1,itemArrey);
lvItem.setAdapter(itemAdapter);
btnRefresh.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
addItemList();
}
});
}
protected void addItemList() {
ArrayList<String> newList = new ArrayList<String>();
try{
newList = RefreshList.GetServerRunningIps();
}
catch (UnknownHostException e){}
catch (IOException e){}
itemArrey = newList;
itemAdapter.notifyDataSetChanged();
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
return super.onOptionsItemSelected(item);
}
/**
* A placeholder fragment containing a simple view.
*/
public static class PlaceholderFragment extends Fragment {
public PlaceholderFragment() {
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_main, container, false);
return rootView;
}
}
}
RefreshList.java:
import java.io.IOException;
import java.net.UnknownHostException;
import java.util.ArrayList;
import java.net.DatagramSocket;
import java.net.DatagramPacket;
import java.net.SocketTimeoutException;
import java.net.SocketException;
import java.net.InetAddress;
public class RefreshList {
public static ArrayList<String> GetServerRunningIps() throws UnknownHostException, IOException
{
ArrayList<String> Res = new ArrayList<String>();
ArrayList<String> Ips = new ArrayList<String>();
Ips = ListIps();
for(int x = 0;x<Ips.size()-1;x++)
{
String CanUse = WaitResponce(Ips.get(x));
if(CanUse.contains("Here"))
{
Res.add(Ips.get(x));
}
else{
Res.add("NOTHING FOUND");
}
}
return Res;
}
private static ArrayList<String> ListIps() throws UnknownHostException, IOException
{
ArrayList<String> Res = new ArrayList<String>();
InetAddress localhost = InetAddress.getLocalHost();
byte[] ip = localhost.getAddress();
for (int i = 1; i <= 254; i++)
{
ip[3] = (byte)i;
InetAddress address = InetAddress.getByAddress(ip);
if (address.isReachable(1000))
{
Res.add(address.toString());
}
}
return Res;
}
private static String WaitResponce(String Ip)
{
DatagramSocket s;
try {
s = new DatagramSocket(5700);
byte[] buf = new byte[1000];
DatagramPacket dp = new DatagramPacket(buf, buf.length);
InetAddress hostAddress = InetAddress.getByName(Ip);
String outString = "ServerCheck_"+InetAddress.getLocalHost().getHostAddress();
buf = outString.getBytes();
DatagramPacket out = new DatagramPacket(buf, buf.length, hostAddress, 5600);
s.send(out);
s.setSoTimeout(2000);
while(true){
try {
s.receive(dp);
String rcvd = new String(dp.getData(), 0, dp.getLength());
return rcvd;
}
catch (SocketTimeoutException e) {
// timeout exception.
s.close();
return new String("Timeout reached!!! ");
}
}
} catch (SocketException e1) {
System.out.println("Socket closed " + e1);
} catch (IOException e) {
e.printStackTrace();
}
return null;
}
}
当我尝试运行它时只返回此错误:
04-06 22:51:32.680 31163-31163/? E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: com.ghhwer.pcremote, PID: 31163
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.ghhwer.pcremote/com.ghhwer.pcremote.Main}: java.lang.NullPointerException
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2209)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2269)
at android.app.ActivityThread.access$800(ActivityThread.java:139)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1210)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:136)
at android.app.ActivityThread.main(ActivityThread.java:5102)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.NullPointerException
at com.ghhwer.pcremote.Main.setUpView(Main.java:45)
at com.ghhwer.pcremote.Main.onCreate(Main.java:31)
at android.app.Activity.performCreate(Activity.java:5248)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1110)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2173)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2269)
at android.app.ActivityThread.access$800(ActivityThread.java:139)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1210)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:136)
at android.app.ActivityThread.main(ActivityThread.java:5102)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
at dalvik.system.NativeStart.main(Native Method)
答案 0 :(得分:0)
您的NullPointerException
是由错误的夸大布局引起的。正如你在这里看到的那样:
setContentView(R.layout.activity_main);
在您的活动中,您要将布局activity_main.xml
和不设置为问题fragment_main.xml
。您的活动尝试查找不在正确布局上的视图。
要避免这种情况,请尝试创建另一个名为activity_main.xml
的布局,然后复制/粘贴(或者应该剪切)其中的所有视图。