我正在使用以下代码为我的聊天应用程序使用适配器实现列表视图。但是当我执行apk时，应用程序退出时说不响应。请建议我改变。
Chatpage.java
public class chatpage extends Activity {
ArrayList<Message> messages;
ListView list;
ChatAdapter adapter;
static String sender = "9876543210";
String receiver;
EditText chatmessage;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.chat);
chatmessage = (EditText) findViewById(R.id.entermessage);
list = (ListView) findViewById(R.id.list);
try {
//adapter = new ChatAdapter(this, messages);
adapter = new ChatAdapter(this, messages);
list.setAdapter(adapter);
addNewMessage(new Message("test msg",false));
chatmessage.setText("hey");
} catch(Exception e) {
chatmessage.setText(e.getMessage());
}
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.start_page, menu);
return true;
}
public void sendMessage() {
chatmessage.setText("send btn clicked");
String msg = chatmessage.getText().toString(); addNewMessage(new
Message(msg, true));
int statusCode;
try {
SendMessageTask task = new SendMessageTask();
task.execute(sender,receiver, msg);
statusCode = task.get();
} catch(Exception e) {
statusCode = 0; // notify error??
}
if (statusCode == 1) { // show a 'check' mark to denote successfulv send
}
else {
// retry
}
// }
// } // remove after push messages feature is available
//receiveMessages();
}
void receiveMessages() {
ArrayList<String> msgs = new ArrayList<String>();
try{
ReceiveMessageTask task = new ReceiveMessageTask();
task.execute();
msgs = task.get();
} catch (Exception e) {
// notify error??
}
for (String m : msgs) {
addNewMessage(new Message(m, false));
}
}
void addNewMessage(Message m) {
messages.add(m);
adapter.notifyDataSetChanged();
list.setSelection(messages.size() - 1);
}
}
ChatAdapter.java
public class ChatAdapter extends BaseAdapter {
private Context mContext;
private ArrayList<Message> mMessages;
public ChatAdapter(Context context, ArrayList<Message> messages) {
super();
// super(context, android.R.layout.simple_list_item_1,messages);
this.mContext = context;
this.mMessages = messages;
}
@Override
public int getCount() {
return mMessages.size();
}
@Override
public Message getItem(int position) {
return mMessages.get(position);
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
Message message = this.getItem(position);
ViewHolder holder;
if (convertView == null) {
holder = new ViewHolder();
convertView = LayoutInflater.from(mContext).inflate(R.layout.bubbledesign, parent, false);
holder.message = (TextView) convertView.findViewById(R.id.message_text);
convertView.setTag(holder);
} else
holder = (ViewHolder) convertView.getTag();
holder.message.setText(message.getMessage());
LayoutParams lp = (LayoutParams) holder.message.getLayoutParams();
// check if it is a status message then remove background, and change
// text color.
if (message.isStatusMessage()) {
holder.message.setBackground(null);
lp.gravity = Gravity.LEFT;
// int c = R.color.textFieldColor;
// holder.message.setTextColor(c);
} else {
// Check whether message is mine to show green background and align
// to right
if (message.isMine()) {
holder.message.setBackgroundResource(R.drawable.bubblenormal);
lp.gravity = Gravity.RIGHT;
}
// If not mine then it is from sender to show orange background and
// align to left
else {
holder.message.setBackgroundResource(R.drawable.bubblenormal);
lp.gravity = Gravity.LEFT;
}
holder.message.setLayoutParams(lp);
// int c = R.color.textColor;
// holder.message.setTextColor(c);
}
return convertView;
}
private static class ViewHolder {
TextView message;
}
@Override
public long getItemId(int position) {
return position;
}
}
Chat.xml
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent" >
<ImageView
android:id="@+id/topImage"
android:layout_width="match_parent"
android:layout_height="60dp"
android:layout_alignParentTop="true"
android:background="#F1760C"
android:contentDescription="topimage"/>
<ImageView
android:id="@+id/bottomImage"
android:layout_width="match_parent"
android:layout_height="400dp"
android:layout_alignParentLeft="true"
android:layout_below="@+id/topImage"
android:background="@drawable/app_background"
android:tileMode="repeat"
android:contentDescription="bottomimage" />
<TextView
android:id="@+id/backtocontacts"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentLeft="true"
android:layout_alignParentTop="true"
android:layout_marginTop="15dp"
android:text="@string/contacts"
android:textAppearance="?android:attr/textAppearanceMedium"
android:textColor="#ffffff"
android:textStyle="bold" />
<TextView
android:id="@+id/usertochat"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentTop="true"
android:layout_centerHorizontal="true"
android:layout_marginTop="15dp"
android:text="Rajat"
android:textAppearance="?android:attr/textAppearanceLarge"
android:textColor="#ffffff"
android:textStyle="bold" />
<RelativeLayout
android:layout_width="match_parent"
android:layout_height="70dp"
android:layout_alignParentBottom="true"
android:layout_alignParentLeft="true"
android:background="#505050">
<TextView
android:id="@+id/add"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_centerVertical="true"
android:layout_marginRight="19dp"
android:text=" +"
android:textAppearance="?android:attr/textAppearanceLarge" />
<EditText
android:id="@+id/entermessage"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentLeft="true"
android:layout_centerVertical="true"
android:layout_marginLeft="22dp"
android:layout_toLeftOf="@+id/sendmessage"
android:background="@drawable/shapes2"
android:ems="10"
android:gravity="center"
android:hint="Type your message here"
android:textStyle="italic" />
<TextView
android:id="@+id/sendmessage"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentRight="true"
android:layout_alignTop="@+id/entermessage"
android:onClick="sendMessage"
android:text="Send"
android:textAppearance="?android:attr/textAppearanceMedium"
android:textSize="20dp" />
</RelativeLayout>
<ListView
android:id="@+id/list"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_centerHorizontal="true"
android:layout_marginBottom="80dp"
android:layout_marginTop="70dp"
app:listitem="@layout/bubbledesign">
</ListView>
</RelativeLayout>
Message.java
public class Message {
/**
* The content of the message
*/
String message;
/**
* Time when message was sent or received
*/
String timeStamp;
/**
* boolean to determine, who is sender of this message
*/
boolean isMine;
/**
* boolean to determine, whether the message is a status message or not. it
* reflects the changes/updates about the sender is writing, have entered
* text etc
*/
boolean isStatusMessage;
/**
* Constructor to make a Message object
*/
public Message(String message, boolean isMine) {
super();
this.message = message;
this.isMine = isMine;
this.isStatusMessage = false;
}
/**
* Constructor to make a status Message object consider the parameters are
* swaped from default Message constructor, not a good approach but have to
* go with it.
*/
public Message(boolean status, String message) {
super();
this.message = message;
this.isMine = false;
this.isStatusMessage = status;
}
public String getMessage() {
return message;
}
public void setMessage(String message) {
this.message = message;
}
public boolean isMine() {
return isMine;
}
public void setMine(boolean isMine) {
this.isMine = isMine;
}
public boolean isStatusMessage() {
return isStatusMessage;
}
public void setStatusMessage(boolean isStatusMessage) {
this.isStatusMessage = isStatusMessage;
}
public String getTimeStamp() {
return timeStamp;
}
public void setTimeStamp(String timeStamp) {
this.timeStamp = timeStamp;
}
}
logcat的：
07-29 15:05:38.778: E/AndroidRuntime(942): FATAL EXCEPTION: main
07-29 15:05:38.778: E/AndroidRuntime(942): java.lang.NullPointerException
07-29 15:05:38.778: E/AndroidRuntime(942): at com.classes.ChatAdapter.getCount(ChatAdapter.java:29)
07-29 15:05:38.778: E/AndroidRuntime(942): at android.widget.AbsListView.onAttachedToWindow(AbsListView.java:2615)
07-29 15:05:38.778: E/AndroidRuntime(942): at android.view.View.dispatchAttachedToWindow(View.java:12125)
07-29 15:05:38.778: E/AndroidRuntime(942): at android.view.ViewGroup.dispatchAttachedToWindow(ViewGroup.java:2450)
07-29 15:05:38.778: E/AndroidRuntime(942): at android.view.ViewGroup.dispatchAttachedToWindow(ViewGroup.java:2457)
07-29 15:05:38.778: E/AndroidRuntime(942): at android.view.ViewGroup.dispatchAttachedToWindow(ViewGroup.java:2457)
07-29 15:05:38.778: E/AndroidRuntime(942): at android.view.ViewGroup.dispatchAttachedToWindow(ViewGroup.java:2457)
07-29 15:05:38.778: E/AndroidRuntime(942): at android.view.ViewGroup.dispatchAttachedToWindow(ViewGroup.java:2457)
07-29 15:05:38.778: E/AndroidRuntime(942): at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1207)
07-29 15:05:38.778: E/AndroidRuntime(942): at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1004)
07-29 15:05:38.778: E/AndroidRuntime(942): at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:5481)
07-29 15:05:38.778: E/AndroidRuntime(942): at android.view.Choreographer$CallbackRecord.run(Choreographer.java:749)
07-29 15:05:38.778: E/AndroidRuntime(942): at android.view.Choreographer.doCallbacks(Choreographer.java:562)
07-29 15:05:38.778: E/AndroidRuntime(942): at android.view.Choreographer.doFrame(Choreographer.java:532)
07-29 15:05:38.778: E/AndroidRuntime(942): at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:735)
07-29 15:05:38.778: E/AndroidRuntime(942): at android.os.Handler.handleCallback(Handler.java:730)
07-29 15:05:38.778: E/AndroidRuntime(942): at android.os.Handler.dispatchMessage(Handler.java:92)
07-29 15:05:38.778: E/AndroidRuntime(942): at android.os.Looper.loop(Looper.java:137)
07-29 15:05:38.778: E/AndroidRuntime(942): at android.app.ActivityThread.main(ActivityThread.java:5103)
07-29 15:05:38.778: E/AndroidRuntime(942): at java.lang.reflect.Method.invokeNative(Native Method)
07-29 15:05:38.778: E/AndroidRuntime(942): at java.lang.reflect.Method.invoke(Method.java:525)
07-29 15:05:38.778: E/AndroidRuntime(942): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
07-29 15:05:38.778: E/AndroidRuntime(942): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
07-29 15:05:38.778: E/AndroidRuntime(942): at dalvik.system.NativeStart.main(Native Method)
答案 0 :(得分：0)
问题在于您的ArrayList<Message> messages，因为它从未在您的代码中初始化。您可以在活动中定义它，然后将其传递给适配器而不进行初始化，这样当适配器运行getCount()方法时，它会尝试返回mMessages的大小，该大小在该点将为空，因此会导致空指针异常。
在活动的onCreate()方法中添加以下行
messages = new ArrayList<Message>();
将它传递给适配器之前。因此，您的onCreate()方法应如下所示。
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.chat);
chatmessage = (EditText) findViewById(R.id.entermessage);
list = (ListView) findViewById(R.id.list);
try {
/** You need the following line added to your code */
messages = new ArrayList<Message>();
adapter = new ChatAdapter(this, messages); //In this line the messages was not initialised in your code
list.setAdapter(adapter);
addNewMessage(new Message("test msg",false));
chatmessage.setText("hey");
} catch(Exception e) {
chatmessage.setText(e.getMessage());
}
}