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我的自定义适配器有一些问题ListView。我不确定我的问题出在 xml 文件、数据还是ListView. NullPointerException当我设置适配器时，我得到了一个。适配器类：

public class InboxAdapter extends BaseAdapter {

    private Context context;

    private List<MailInbox> mails;

    public InboxAdapter(Context context, List<MailInbox> mails)
    {
        this.context = context;
        this.mails = mails;
    }

    @Override
    public int getCount() {
        return mails.size();
    }

    @Override
    public Object getItem(int item) {
        return mails.get(item);
    }

    @Override
    public long getItemId(int position) {
        return position;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup viewGroup) {

        MailInbox entry = mails.get(position);

        if(convertView == null)
        {
            LayoutInflater inflater = (LayoutInflater)context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
            convertView = inflater.inflate(R.layout.mail_list_row, null);
        }

        ImageView mailImg = (ImageView)convertView.findViewById(R.id.mail_thumb);
        boolean read = entry.IsRead;

        if(read)
        {
            //Set "read" image
            mailImg.setImageResource(R.drawable.message);
        } else
        {
            //Set "unread" image
            mailImg.setImageResource(R.drawable.message);
        }

        TextView author = (TextView)convertView.findViewById(R.id.mail_text);
        TextView body = (TextView)convertView.findViewById(R.id.mail_detail);
        TextView date = (TextView)convertView.findViewById(R.id.mail_date);

        author.setText(entry.AuthorName);
        body.setText(entry.MessageBody);
        date.setText(entry.CreatedAt);

        return convertView;
    }
}

Activity我使用它的地方：

public class InboxActivity extends SherlockActivity 
{
    private ListView list;
    private GetMessagesConnection mMessages;

    public String kidID;

    public InboxActivity() {
        // TODO Auto-generated constructor stub
    }

    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        setContentView(R.layout.inbox_layout);        

        Bundle extras = getIntent().getExtras();
        if(extras != null)
        {
            kidID = extras.getString("kidID");
        }

        new GetMails().execute();
    }

    private void setUpList()
    {
        list = (ListView)findViewById(R.id.mail_list);      

        ArrayList<MailInbox> mails = new ArrayList<MailInbox>();

        for(int i = 0; i < mMessages.myMail.size(); i++)
        {
            MailInbox inbox = new MailInbox();

            inbox.AuthorName = mMessages.myMail.get(i).AuthorName;
            inbox.CreatedAt = mMessages.myMail.get(i).CreatedAt;
            inbox.MessageBody = mMessages.myMail.get(i).MessageBody;
            inbox.IsRead = mMessages.myMail.get(i).IsRead;

            System.out.println("Author: " + inbox.AuthorName);
            System.out.println("Time: " + inbox.CreatedAt);
            System.out.println("Message: " + inbox.MessageBody);
            System.out.println("Read: " + inbox.IsRead);

            mails.add(inbox);
        }

        int length = mails.size();
        System.out.println("Size: " + length);

        InboxAdapter adapter = new InboxAdapter(this, mails);

        // It crashes here with a Nullpointer Exception
        list.setAdapter(adapter);
    }

    private class GetMails extends AsyncTask<Void, Void, Void> implements DialogInterface.OnCancelListener
    {
        private ProgressDialog dialog;

        protected void onPreExecute()
        {
                dialog = ProgressDialog.show(InboxActivity.this, "", "Henter beskeder...", true);
        }

        protected Void doInBackground(Void... unused)
        {
                mMessages = new GetMessagesConnection();

                mMessages.kidID = kidID;

                mMessages.connection();

                return null;
        }

        protected void onPostExecute(Void unused)
        {           
            dialog.dismiss();
            setUpList();
        }

        public void onCancel(DialogInterface dialog)
        {
            cancel(true);
            dialog.dismiss();
        }
    }
}

*邮件列表*：

<?xml version="1.0" encoding="utf-8"?>
<ListView xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/mail_list"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:layout_weight="2" >    
</ListView>

*mail_list_row*:

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="48dip"
    android:background="@drawable/listselector"
    >
    <ImageView
        android:id="@+id/mail_thumb"
        android:layout_width="30dip"
        android:layout_height="30dip"
        android:layout_centerVertical="true"
        android:layout_alignParentLeft="true"
        android:contentDescription="@string/imgdesc"
        />
    <TextView
        android:id="@+id/mail_text"
        android:layout_toRightOf="@+id/mail_thumb"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textSize="14dip"
        android:layout_marginLeft="8dip"
        android:layout_centerVertical="false"
        android:singleLine="true"
        android:ellipsize="end"
        android:textStyle="bold"
        android:textColor="@android:color/white"
        />
    <TextView 
        android:id="@+id/mail_detail"
        android:layout_toRightOf="@+id/mail_thumb"
        android:layout_below="@+id/mail_text"
        android:layout_width="100dip"
        android:layout_height="wrap_content"
        android:textSize="12dip"
        android:layout_marginLeft="8dip"
        android:layout_centerVertical="false"
        android:singleLine="true"
        android:ellipsize="end"
        android:textColor="@color/grey"     
        />
    <TextView 
        android:id="@+id/mail_date"
        android:layout_toRightOf="@+id/mail_detail"
        android:layout_below="@+id/mail_text"
        android:layout_width="100dip"
        android:layout_height="wrap_content"
        android:textSize="12dip"
        android:singleLine="true"
        android:ellipsize="end"
        android:textColor="@color/grey"
        android:layout_alignParentRight="true"      
        />
</RelativeLayout>

我不知道可能是什么null。我已经尝试解决这个问题几个小时了。错误日志：

05-14 19:55:45.525: E/AndroidRuntime(2509): FATAL EXCEPTION: main
05-14 19:55:45.525: E/AndroidRuntime(2509): java.lang.NullPointerException
05-14 19:55:45.525: E/AndroidRuntime(2509):     at com.cim.daycare.InboxActivity.setUpList(InboxActivity.java:75)
05-14 19:55:45.525: E/AndroidRuntime(2509):     at com.cim.daycare.InboxActivity.access$2(InboxActivity.java:36)
05-14 19:55:45.525: E/AndroidRuntime(2509):     at com.cim.daycare.InboxActivity$GetMails.onPostExecute(InboxActivity.java:101)
05-14 19:55:45.525: E/AndroidRuntime(2509):     at com.cim.daycare.InboxActivity$GetMails.onPostExecute(InboxActivity.java:1)
05-14 19:55:45.525: E/AndroidRuntime(2509):     at android.os.AsyncTask.finish(AsyncTask.java:417)
05-14 19:55:45.525: E/AndroidRuntime(2509):     at android.os.AsyncTask.access$300(AsyncTask.java:127)
05-14 19:55:45.525: E/AndroidRuntime(2509):     at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:429)
05-14 19:55:45.525: E/AndroidRuntime(2509):     at android.os.Handler.dispatchMessage(Handler.java:99)
05-14 19:55:45.525: E/AndroidRuntime(2509):     at android.os.Looper.loop(Looper.java:123)
05-14 19:55:45.525: E/AndroidRuntime(2509):     at android.app.ActivityThread.main(ActivityThread.java:3683)
05-14 19:55:45.525: E/AndroidRuntime(2509):     at java.lang.reflect.Method.invokeNative(Native Method)
05-14 19:55:45.525: E/AndroidRuntime(2509):     at java.lang.reflect.Method.invoke(Method.java:507)
05-14 19:55:45.525: E/AndroidRuntime(2509):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
05-14 19:55:45.525: E/AndroidRuntime(2509):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
05-14 19:55:45.525: E/AndroidRuntime(2509):     at dalvik.system.NativeStart.main(Native Method)
4

2 回答 2

2

In the activity InboxActivity you set the content view to R.layout.inbox_layout(I don't see this file in your question) and you search for the ListView with the id R.id.mail_list. A ListView with this id exist in the mail_list.xml file. Are you sure that the content view for the InboxActivity isn't R.layout.mail_list:

//...
public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.mail_list);        
        Bundle extras = getIntent().getExtras();
//...

Also:

  • Please don't declare a constructor for the InboxActivity, initialize what you want in the onCreate method(this is how things work in the android world).

  • Do you handle the cases when extras is null? (If the extras is null then kidID will also be null and this could put you in trouble in the GetMessagesConnection class if you don't handle this scenario).

于 2012-05-14T18:19:57.433 回答
1

You get the instance to your list like this list = (ListView)findViewById(R.id.mail_list); which means you are checking your current layout for that ID, but your current layout is set to setContentView(R.layout.inbox_layout);

What is inbox_layout? You haven't showed us the XML?Did you mean to set it to setContentView(R.layout.mail_list); instead?

Edit: Also, you may want to look into using a ViewHolder in your custom adapter to avoid making repetitive calls to findViewByID(...). Take a look at this tutorial: http://xjaphx.wordpress.com/2011/06/16/viewholder-pattern-caching-view-efficiently/

于 2012-05-14T18:21:55.747 回答