我制作了一个片段，它往往显示数据库中的注释列表视图，每个项目都有3个文本视图：主题，内容和所有者，但是当按下列表按钮显示列表视图时出错，似乎我的函数showList出现了问题但是没有不知道为什么，这是我的logcat和代码。感谢任何提前帮助我的坏英语！
12-11 00:36:13.961: E/AndroidRuntime(779): FATAL EXCEPTION: main
12-11 00:36:13.961: E/AndroidRuntime(779): java.lang.NullPointerException
12-11 00:36:13.961: E/AndroidRuntime(779): at com.bblackbb.jotdownv2.WhiteNote.showNoteList(WhiteNote.java:117)
12-11 00:36:13.961: E/AndroidRuntime(779): at com.bblackbb.jotdownv2.WhiteNote.access$1(WhiteNote.java:109)
12-11 00:36:13.961: E/AndroidRuntime(779): at com.bblackbb.jotdownv2.WhiteNote$2.onClick(WhiteNote.java:92)
12-11 00:36:13.961: E/AndroidRuntime(779): at android.view.View.performClick(View.java:4084)
12-11 00:36:13.961: E/AndroidRuntime(779): at android.view.View$PerformClick.run(View.java:16966)
12-11 00:36:13.961: E/AndroidRuntime(779): at android.os.Handler.handleCallback(Handler.java:615)
12-11 00:36:13.961: E/AndroidRuntime(779): at android.os.Handler.dispatchMessage(Handler.java:92)
2-11 00:36:13.961: E/AndroidRuntime(779): at android.os.Looper.loop(Looper.java:137)
12-11 00:36:13.961: E/AndroidRuntime(779): at android.app.ActivityThread.main(ActivityThread.java:4745)
12-11 00:36:13.961: E/AndroidRuntime(779): at java.lang.reflect.Method.invokeNative(Native Method)
WhiteNote.java
public class WhiteNote extends Fragment {
private NoteDatabase note_database;
private int i=0;
public Context context;
public NoteListAdapter noteListAdapter;
public ListView note_listview_container;
static SQLiteDatabase note_db;
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
final View rootView = inflater.inflate(R.layout.white_note, container, false);
context=getActivity();
note_database = new NoteDatabase(context);
final EditText text_ed_1;
final EditText text_ed_2;
Button button_addNote;
Button button_listallNote;
Button button_delallNote;
//final TextView note_list;
//final LinearLayout note_container;
text_ed_1 = (EditText)rootView.findViewById(R.id.textedit1);
text_ed_2 = (EditText)rootView.findViewById(R.id.textedit2);
button_addNote = (Button)rootView.findViewById(R.id.button1);
button_listallNote = (Button)rootView.findViewById(R.id.button2);
button_delallNote = (Button)rootView.findViewById(R.id.button3);
//note_list=(TextView)rootView.findViewById(R.id.textview1);
//note_container = (LinearLayout)rootView.findViewById(R.id.listcontainer);
note_listview_container=(ListView)rootView.findViewById(R.id.note_listview);
//showNoteList();
button_addNote.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
note_database.open();
note_database.createData(text_ed_1.getText().toString(),text_ed_2.getText().toString());
//i++;
note_database.close();
}
});
button_listallNote.setOnClickListener(new OnClickListener(){
@Override
public void onClick(View v) {
note_database.open();
//String ds = note_database.getData();
showNoteList();
note_database.close();
//note_list.setText(ds);
}
});
button_delallNote.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
note_database.open();
note_database.deleteAllNote();
note_database.close();
}
});
return rootView;
}
private void showNoteList() {
ArrayList<NoteItems> noteList = new ArrayList<NoteItems>();
noteList.clear();
note_database.open();
String[] columns = new String[] {note_database.COLUMN_ID,note_database.COLUMN_TOPIC,note_database.COLUMN_NOTECONTENT,note_database.COLUMN_NAME};
Cursor c = note_db.query(note_database.TABLE_NOTE, columns, null, null, null, null, null);
int iRow = c.getColumnIndex(note_database.COLUMN_ID);
int iTopic = c.getColumnIndex(note_database.COLUMN_TOPIC);
int iContent = c.getColumnIndex(note_database.COLUMN_NOTECONTENT);
int iOwner = c.getColumnIndex(note_database.COLUMN_NAME);
for(c.moveToFirst(); !c.isAfterLast(); c.moveToNext()){
NoteItems one_rowItems = new NoteItems();
one_rowItems.set_rowTopic(c.getString(iTopic));
one_rowItems.set_rowContent(c.getString(iContent));
one_rowItems.set_rowOwner(c.getString(iOwner));
noteList.add(one_rowItems);
}
c.close();
note_database.close();
noteListAdapter = new NoteListAdapter(getActivity(), noteList);
note_listview_container.setAdapter(noteListAdapter);
}
}
NoteDatabase.java
public class NoteDatabase {
private static final String DATABASE_NAME = "DB_NOTE";
private static final int DATABASE_VERSION = 1;
public static final String TABLE_NOTE = "NOTE";
public static final String COLUMN_ID = "_id";
public static final String COLUMN_TOPIC = "Topic";
public static final String COLUMN_NOTECONTENT = "Content";
public static final String COLUMN_NAME = "Name";
private static Context my_context;
static SQLiteDatabase note_sqldb;
private OpenHelper noteopenHelper;
public NoteDatabase(Context c){
NoteDatabase.my_context = c;
}
public NoteDatabase open() throws SQLException{
noteopenHelper = new OpenHelper(my_context);
note_sqldb = noteopenHelper.getWritableDatabase();
return this;
}
public void close(){
noteopenHelper.close();
}
public long createData(String chude_note, String noidung_note) {
ContentValues cv = new ContentValues();
cv.put(COLUMN_TOPIC, chude_note);
cv.put(COLUMN_NOTECONTENT, noidung_note);
cv.put(COLUMN_NAME, "by Black");
return note_sqldb.insert(TABLE_NOTE, null, cv);
}
public String getData() {
String[] columns = new String[] {COLUMN_ID,COLUMN_TOPIC,COLUMN_NOTECONTENT,COLUMN_NAME};
Cursor c = note_sqldb.query(TABLE_NOTE, columns, null, null, null, null, null);
/*if(c==null)
Log.v("Cursor", "C is NULL");*/
String result="";
int iRow = c.getColumnIndex(COLUMN_ID);
int iTopic = c.getColumnIndex(COLUMN_TOPIC);
int iContent = c.getColumnIndex(COLUMN_NOTECONTENT);
int iOwner = c.getColumnIndex(COLUMN_NAME);
for(c.moveToFirst(); !c.isAfterLast(); c.moveToNext()){
result = result +" \n"+ c.getString(iRow)
+ "\n - Topic: " + c.getString(iTopic)
+ "\n - Content: " + c.getString(iContent)
+ "\n - Owner: " + c.getString(iOwner) + "\n";
}
c.close();
//Log.v("Result", result);
return result;
}
public Cursor selectQuery(String query) {
Cursor c1 = null;
try {
if (note_sqldb.isOpen()) {
note_sqldb.close();
}
note_sqldb = noteopenHelper.getWritableDatabase();
c1 = note_sqldb.rawQuery(query, null);
} catch (Exception e) {
System.out.println("DATABASE ERROR " + e);
}
return c1;
}
/*Ham xoa 1 note */
public int deleteNote(String topic) {
return note_sqldb.delete(TABLE_NOTE, COLUMN_TOPIC + "='" + topic + "'", null);
}
/*Ham xoa toan bo table NOTE*/
public int deleteAllNote() {
return note_sqldb.delete(TABLE_NOTE, null, null);
}
//---------------- class OpenHelper ------------------
private static class OpenHelper extends SQLiteOpenHelper {
public OpenHelper(Context context) {
super(context, DATABASE_NAME, null, DATABASE_VERSION);
}
@Override
public void onCreate(SQLiteDatabase arg0) {
arg0.execSQL("CREATE TABLE " + TABLE_NOTE + " ("
+ COLUMN_ID + " INTEGER PRIMARY KEY, "
+ COLUMN_TOPIC + " TEXT NOT NULL, "
+ COLUMN_NOTECONTENT + " TEXT NOT NULL, "
+ COLUMN_NAME + " TEXT NOT NULL);");
}
@Override
public void onUpgrade(SQLiteDatabase arg0, int arg1, int arg2) {
arg0.execSQL("DROP TABLE IF EXISTS " + TABLE_NOTE);
onCreate(arg0);
}
}
}
NoteItems.java
public class NoteItems {
private String note_row_topic;
private String note_row_content;
private String note_row_owner;
public String get_rowTopic() {
return note_row_topic;
}
public void set_rowTopic(String topic) {
this.note_row_topic = topic;
}
public String get_rowContent() {
return note_row_content;
}
public void set_rowContent(String content) {
this.note_row_content = content;
}
public String get_rowOwner() {
return note_row_owner;
}
public void set_rowOwner(String owner) {
this.note_row_owner = owner;
}
@Override
public String toString() {
return "[ Topic=" + note_row_topic + ", content =" +
note_row_content + " , owner=" + note_row_owner + "]";
}
}
NoteListAdapter.java
public class NoteListAdapter extends BaseAdapter {
Context mcontext;
ArrayList<NoteItems> noteList;
public NoteListAdapter(Context context, ArrayList<NoteItems> list) {
this.mcontext = context;
noteList = list;
}
@Override
public int getCount() {
return noteList.size();
}
@Override
public Object getItem(int position) {
return noteList.get(position);
}
@Override
public long getItemId(int position) {
return position;
}
@Override
public View getView(int position, View convertView, ViewGroup arg2) {
NoteItems noteListItems = noteList.get(position);
if (convertView == null) {
LayoutInflater inflater = (LayoutInflater) mcontext.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
convertView = inflater.inflate(R.layout.listview_row, null);
}
TextView noteTopic = (TextView) convertView.findViewById(R.id.row_topic);
noteTopic.setText(noteListItems.get_rowTopic());
TextView noteContent = (TextView) convertView.findViewById(R.id.row_content);
noteContent.setText(noteListItems.get_rowContent());
TextView noteOwner = (TextView) convertView.findViewById(R.id.row_owner);
noteOwner.setText(noteListItems.get_rowOwner());
return convertView;
}
}