在构建一个页面，用户将在我的Android应用程序上发送彼此的消息，并且我使用listview显示发送或接收的所有消息。对于初始测试，我试图给自己发送一条消息，但它崩溃了应用程序，错误消息让我感到困惑。它说
07-17 02:38:26.847: E/AndroidRuntime(2581): FATAL EXCEPTION: main
07-17 02:38:26.847: E/AndroidRuntime(2581): java.lang.NullPointerException
07-17 02:38:26.847: E/AndroidRuntime(2581): at android.widget.SimpleAdapter.getCount(SimpleAdapter.java:93)
07-17 02:38:26.847: E/AndroidRuntime(2581): at android.widget.ListView.setAdapter(ListView.java:460)
07-17 02:38:26.847: E/AndroidRuntime(2581): at android.app.ListActivity.setListAdapter(ListActivity.java:265)
07-17 02:38:26.847: E/AndroidRuntime(2581): at com.example.reflaptry1.SendMessage$1.onClick(SendMessage.java:39)
07-17 02:38:26.847: E/AndroidRuntime(2581): at android.view.View.performClick(View.java:4084)
07-17 02:38:26.847: E/AndroidRuntime(2581): at android.view.View$PerformClick.run(View.java:16966)
07-17 02:38:26.847: E/AndroidRuntime(2581): at android.os.Handler.handleCallback(Handler.java:615)
07-17 02:38:26.847: E/AndroidRuntime(2581): at android.os.Handler.dispatchMessage(Handler.java:92)
07-17 02:38:26.847: E/AndroidRuntime(2581): at android.os.Looper.loop(Looper.java:137)
07-17 02:38:26.847: E/AndroidRuntime(2581): at android.app.ActivityThread.main(ActivityThread.java:4745)
07-17 02:38:26.847: E/AndroidRuntime(2581): at java.lang.reflect.Method.invokeNative(Native Method)
07-17 02:38:26.847: E/AndroidRuntime(2581): at java.lang.reflect.Method.invoke(Method.java:511)
07-17 02:38:26.847: E/AndroidRuntime(2581): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
07-17 02:38:26.847: E/AndroidRuntime(2581): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
07-17 02:38:26.847: E/AndroidRuntime(2581): at dalvik.system.NativeStart.main(Native Method)
以下是sendMessage类的内容
import java.util.ArrayList;
import java.util.HashMap;
import android.app.ListActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ListAdapter;
import android.widget.SimpleAdapter;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemClickListener;
public class SendMessage extends ListActivity {
ArrayList<HashMap<String, String>> messageList;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_send_message);
Button sendText=(Button)findViewById(R.id.sendChat);
sendText.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
EditText editMsg=(EditText)findViewById(R.id.theMessage);
String msg=editMsg.getText().toString();
HashMap<String, String> msgList=new HashMap<String, String>();
msgList.put("yourMsg",msg);
ListAdapter adapter= new SimpleAdapter(
SendMessage.this, messageList,
R.layout.list_message, new String[]{"yourMsg"},
new int[]{R.id.senderMessage});
setListAdapter(adapter);
}
});
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.send_message, menu);
return true;
}
}
这是我的list_message.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:orientation="vertical" >
<!-- Product id (pid) - will be HIDDEN - used to pass to other activity -->
<TextView
android:id="@+id/pid"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:visibility="gone" />
<!-- Name Label -->
<TextView
android:id="@+id/senderName"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:paddingTop="16dip"
android:paddingBottom="16dip"
android:paddingLeft="16dip"
/>
<TextView
android:id="@+id/senderMessage"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
/>
</LinearLayout>
和我的activity_send_message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:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context=".SendMessage" >
<EditText
android:id="@+id/theMessage"
android:layout_width="220dp"
android:layout_height="wrap_content"
android:layout_alignParentBottom="true"
android:layout_marginBottom="15dp"
android:ems="10"
android:hint="@string/write" />
<ListView
android:id="@android:id/list"
android:layout_width="fill_parent"
android:layout_height="350dp"
android:layout_above="@+id/theMessage"
android:layout_alignLeft="@+id/theMessage"
android:layout_marginBottom="14dp" >
</ListView>
<Button
android:id="@+id/sendChat"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignTop="@+id/theMessage"
android:layout_toRightOf="@+id/theMessage"
android:text="@string/button_send" />
</RelativeLayout>
所以是的，我真的不会发生什么问题。
答案 0 :(得分：1)
答案 1 :(得分：1)
这可以帮助你..
SimpleAdapter的构造函数将参数2中的List视为：SimpleAdapter(Context context, List<? extends Map<String, ?>> data, int resource, String[] from, int[] to);
所以，这样做是为了在Adapter中添加值对：
List<HashMap<String, String>> aList = new ArrayList<HashMap<String, String>>();
HashMap<String, String> hm = new HashMap<String, String>();
HashMap<String, String> hm1 = new HashMap<String, String>();
hm.put("Name","abc");
hm1.put("Password","abc");
aList.add(hm);
答案 2 :(得分：0)
您正在将messageList传递给适配器，但您从未创建该列表ArrayList<HashMap<String, String>> messageList;，因此当您传递它时它将为null。