我正在设计与Whatsapp应用程序（显示聊天）界面相同的布局...有一些错误我不知道发生了什么......
package com.example.coder;
import java.util.ArrayList;
import java.util.List;
import com.example.coder.Custom.Row;
import com.example.coder.CustomArrayAdapter.ViewHolder;
import com.example.coder.Whats.MessageData;
import android.app.Activity;
import android.app.ListActivity;
import android.content.Context;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.View.OnClickListener;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ImageView;
import android.widget.ListView;
import android.widget.TextView;
public class Whats extends Activity {
MessageAdapter<MessageData> adapter;
EditText message;
List<MessageData> msgs;
Button b;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.whats_helper);
message = (EditText) findViewById(R.id.enter_message);
ListView lv = (ListView) findViewById(R.id.list);
msgs = new ArrayList<MessageData>();
b=(Button)findViewById(R.id.send_button);
adapter=new MessageAdapter<MessageData>(this,R.layout.whats,msgs);
lv.setAdapter(adapter);
}
public void sendMessage() {
String mText = message.getText().toString();
msgs.add(new MessageData(mText));
adapter.notifyDataSetChanged();
message.setText("");
}
public class MessageData {
private String message;
public MessageData(String message) {
this.message = message;
}
public void setMessage(String message) {
this.message = message;
}
public String getMessage() {
return message;
}
}
public class MessageAdapter<T> extends ArrayAdapter<MessageData> {
Context context;
public MessageAdapter(Context context,int resource, List<MessageData> objs) {
super(context,resource,objs);
this.context=context;
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
MessageView msgView = null;
LayoutInflater mInflater = (LayoutInflater) context.getSystemService(Activity.LAYOUT_INFLATER_SERVICE);
if(convertView == null)
{
// Get a new instance of the row layout view
convertView = mInflater.inflate(R.layout.whats, null);
// Hold the view objects in an object,
// so they don't need to be re-fetched
msgView = new MessageView();
msgView.msg = (TextView) convertView.findViewById(R.id.message_text);
// Cache the view objects in the tag,
// so they can be re-accessed later
convertView.setTag(msgView);
} else {
msgView = (MessageView) convertView.getTag();
}
// Transfer the stock data from the data object
// to the view objects
MessageData currentMsg = getItem(position);
msgView.msg.setText(currentMsg.getMessage());
return convertView;
}
class MessageView {
TextView msg;
}
}
}
Whats活动的布局这是Whats活动使用的布局......
<LinearLayout 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"
tools:context=".MainActivity"
android:orientation="vertical">
<!--<FrameLayout-->
<!--android:background="@color/header_color"-->
<!--android:layout_width="match_parent"-->
<!--android:layout_height="0dp"-->
<!--android:layout_weight="1">-->
<!--</FrameLayout>-->
<LinearLayout
android:layout_width="match_parent"
android:orientation="vertical"
android:layout_height="0dp"
android:layout_weight="10">
<FrameLayout
android:layout_height="0dp"
android:layout_width="match_parent"
android:layout_weight="11">
<ListView
android:id="@+android:id/list"
android:drawSelectorOnTop="false"
android:layout_height="match_parent"
android:layout_width="match_parent"
android:footerDividersEnabled="true">
</ListView>
</FrameLayout>
<FrameLayout
android:layout_height="0dp"
android:layout_width="match_parent"
android:layout_weight="1">
<LinearLayout
android:layout_height="match_parent"
android:layout_width="match_parent"
android:id="@+id/linearLayout">
<EditText
android:id="@+id/enter_message"
android:layout_width="0dp"
android:layout_height="match_parent"
android:layout_weight="1"
android:hint="edit_text" />
<Button
android:id="@+id/send_button"
android:layout_width="45dp"
android:layout_height="30dp"
android:onClick="sendMessage"/>
</LinearLayout>
</FrameLayout>
</LinearLayout>
</LinearLayout>
单个文字的布局
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="fill_parent"
android:gravity="fill_horizontal"
android:layout_height="wrap_content">
<RelativeLayout
android:layout_height="wrap_content"
android:layout_width="match_parent">
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:gravity="right"
android:layout_marginTop="@dimen/activity_horizontal_margin"
android:id="@+id/message_text" />
</RelativeLayout>
</LinearLayout>
* 错误日志*
02-05 21:41:58.560: E/AndroidRuntime(2346): in writeCrashedAppName, pkgName :com.example.coder
02-05 21:41:58.560: D/AndroidRuntime(2346): file written successfully with content: com.example.coder StringBuffer : ;com.example.coder
02-05 21:41:58.570: I/Process(2346): Sending signal. PID: 2346 SIG: 9
02-05 21:41:58.570: E/AndroidRuntime(2346): FATAL EXCEPTION: main
02-05 21:41:58.570: E/AndroidRuntime(2346): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.coder/com.example.coder.Whats}: java.lang.NullPointerException
02-05 21:41:58.570: E/AndroidRuntime(2346): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1647)
02-05 21:41:58.570: E/AndroidRuntime(2346): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1663)
02-05 21:41:58.570: E/AndroidRuntime(2346): at android.app.ActivityThread.access$1500(ActivityThread.java:117)
02-05 21:41:58.570: E/AndroidRuntime(2346): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:931)
02-05 21:41:58.570: E/AndroidRuntime(2346): at android.os.Handler.dispatchMessage(Handler.java:99)
02-05 21:41:58.570: E/AndroidRuntime(2346): at android.os.Looper.loop(Looper.java:130)
02-05 21:41:58.570: E/AndroidRuntime(2346): at android.app.ActivityThread.main(ActivityThread.java:3683)
02-05 21:41:58.570: E/AndroidRuntime(2346): at java.lang.reflect.Method.invokeNative(Native Method)
02-05 21:41:58.570: E/AndroidRuntime(2346): at java.lang.reflect.Method.invoke(Method.java:507)
02-05 21:41:58.570: E/AndroidRuntime(2346): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:880)
02-05 21:41:58.570: E/AndroidRuntime(2346): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:638)
02-05 21:41:58.570: E/AndroidRuntime(2346): at dalvik.system.NativeStart.main(Native Method)
02-05 21:41:58.570: E/AndroidRuntime(2346): Caused by: java.lang.NullPointerException
02-05 21:41:58.570: E/AndroidRuntime(2346): at com.example.coder.Whats.onCreate(Whats.java:44)
02-05 21:41:58.570: E/AndroidRuntime(2346): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1049)
02-05 21:41:58.570: E/AndroidRuntime(2346): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1611)
答案 0 :(得分：1)
我会说你的ListView因此而为null：
<ListView
android:id="@+android:id/list"
将其替换为
android:id="@+id/list"