public class ListDataAdapter extends ArrayAdapter {
List list = new ArrayList();
public ListDataAdapter(Context context, int resource) {
super(context, resource);
}
static class LayoutHandler{
TextView id,subject, assignment, dueDate, notes;
}
@Override
public long getItemId(int position) {
return super.getItemId(position);
}
@Override
public void add(Object object) {
super.add(object);
list.add(object);
}
@Override
public int getCount() {
return list.size();
}
@Override
public Object getItem(int position) {
return list.get(position);
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
View row = convertView;
LayoutHandler layoutHandler;
if(row==null){
LayoutInflater layoutInflater = (LayoutInflater)this.getContext().getSystemService(Context.LAYOUT_INFLATER_SERVICE);
row=layoutInflater.inflate(R.layout.row_layout_listview,parent,false);
layoutHandler = new LayoutHandler();
layoutHandler.id =(TextView)row.findViewById(R.id.TEXTid);
layoutHandler.subject = (TextView)row.findViewById(R.id.textSubject);
layoutHandler.assignment = (TextView)row.findViewById(R.id.textAssignment);
layoutHandler.dueDate = (TextView)row.findViewById(R.id.textDueDate);
layoutHandler.notes = (TextView)row.findViewById(R.id.notesTextField);
notifyDataSetChanged();
row.setTag(layoutHandler);
}
else{
layoutHandler = (LayoutHandler)row.getTag();
notifyDataSetChanged();
}
DataProvider dataProvider = (DataProvider)this.getItem(position);
layoutHandler.id.setText(dataProvider.getAssignmentValue());
layoutHandler.subject.setText(dataProvider.getSubject());
layoutHandler.assignment.setText(dataProvider.getAssignment());
layoutHandler.dueDate.setText(dataProvider.getDueDate());
layoutHandler.notes.setText(dataProvider.getNotes());
notifyDataSetChanged();
return row;
}
}
public class MainActivity extends Activity {
ListView listView;
SQLiteDatabase sqLiteDatabase;
DbHelper dbHelper;
ListDataAdapter listDataAdapter;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);//
dbHelper = new DbHelper(getApplicationContext());//
sqLiteDatabase = dbHelper.getWritableDatabase();//
listView = (ListView) findViewById(R.id.listView3);
listDataAdapter = new ListDataAdapter(getApplicationContext(), R.layout.row_layout_listview);
listView.setAdapter(listDataAdapter);
Cursor cursor = dbHelper.getUpcomingAssignment(sqLiteDatabase);
if (cursor.moveToFirst()) {
do {
final String module, assignment, dueDate, weighting, notes, thisid;
thisid = cursor.getString(0);
module = cursor.getString(1);
assignment = cursor.getString(3);
dueDate = cursor.getString(4);
weighting = cursor.getString(2);
notes = cursor.getString(5);
DataProvider dataProvider = new DataProvider(weighting, module, assignment, dueDate, notes, thisid);
listDataAdapter.add(dataProvider);
}while (cursor.moveToNext());
}
}
06-27 15:42:39.118 2988-2988/com.ulsteruniversity.eamonn.diary1905 I/art﹕ Late-enabling -Xcheck:jni
06-27 15:42:39.384 2988-2988/com.ulsteruniversity.eamonn.diary1905 E/Database Operations﹕ Database opened/created from constructor.
06-27 15:42:39.386 2988-2988/com.ulsteruniversity.eamonn.diary1905 D/AndroidRuntime﹕ Shutting down VM
06-27 15:42:39.387 2988-2988/com.ulsteruniversity.eamonn.diary1905 E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: com.ulsteruniversity.eamonn.diary1905, PID: 2988
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.ulsteruniversity.eamonn.diary1905/com.ulsteruniversity.eamonn.diary1905.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.database.Cursor android.database.sqlite.SQLiteDatabase.rawQuery(java.lang.String, java.lang.String[])' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2325)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2387)
at android.app.ActivityThread.access$800(ActivityThread.java:151)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1303)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5254)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.database.Cursor android.database.sqlite.SQLiteDatabase.rawQuery(java.lang.String, java.lang.String[])' on a null object reference
at com.ulsteruniversity.eamonn.diary1905.DbHelper.getUpcomingAssignment(DbHelper.java:186)
at com.ulsteruniversity.eamonn.diary1905.MainActivity.onCreate(MainActivity.java:63)
at android.app.Activity.performCreate(Activity.java:5990)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1106)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2278)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2387)
at android.app.ActivityThread.access$800(ActivityThread.java:151)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1303)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5254)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)
我创建了一个小型应用程序来跟踪大学作业。使用sqlite数据库，用户可以存储分配名称，到期日期和分配注释等信息。我创建了一个列表视图，该列表视图将显示即将到来的作业，因此任何作业将在接下来的7天内到期。我似乎无法得到正确的查询，任何可以帮助的人？感谢
//My DbHelper class
public class DbHelper extends SQLiteOpenHelper {
public static final String ASSIGNMENT_ID = "_id";
public static final String ASSIGNMENT_VALUE = "assignment_value";
public static final String SUBJECT = "subject";
public static final String ASSIGNMENT_TITLE = "assignment_title";
public static final String DUE_DATE = "due_date";
public static final String NOTES_ASSIGNMENT = "notes";
public static final String TABLE_NAME_ASSIGNMENT = "assignment_information";
private static final String DATABASE_NAME = "assignment_info.db";
private static final String ADD_QUERY = "CREATE TABLE "+
TABLE_NAME_ASSIGNMENT+"("+
ASSIGNMENT_ID+" INTEGER PRIMARY KEY AUTOINCREMENT,"+
SUBJECT+" TEXT,"+
ASSIGNMENT_VALUE+" INTEGER,"+
ASSIGNMENT_TITLE+" TEXT,"+
DUE_DATE+" DATETIME,"+
NOTES_ASSIGNMENT+" TEXT);";
//My query (so far) to return a cursor with the selected assignments
public Cursor getUpcomingAssignment(SQLiteDatabase sqLiteDatabase){
GregorianCalendar gc = new GregorianCalendar();
SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
String today = sdf.format(gc.getTime());
String sql = "SELECT * FROM " + TABLE_NAME_ASSIGNMENT + " WHERE "+ DUE_DATE + " >= date('now', '+7 days')";
Cursor mycursor = sqLiteDatabase.rawQuery(sql, null);
return mycursor;
}
06-27 15:23:54.187 27174-27174/com.ulsteruniversity.eamonn.diary1905 D/AndroidRuntime﹕ Shutting down VM
06-27 15:23:54.188 27174-27174/com.ulsteruniversity.eamonn.diary1905 E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: com.ulsteruniversity.eamonn.diary1905, PID: 27174
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.ulsteruniversity.eamonn.diary1905/com.ulsteruniversity.eamonn.diary1905.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.database.Cursor com.ulsteruniversity.eamonn.diary1905.DbHelper.getUpcomingAssignment(android.database.sqlite.SQLiteDatabase)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2325)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2387)
at android.app.ActivityThread.access$800(ActivityThread.java:151)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1303)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5254)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.database.Cursor com.ulsteruniversity.eamonn.diary1905.DbHelper.getUpcomingAssignment(android.database.sqlite.SQLiteDatabase)' on a null object reference
at com.ulsteruniversity.eamonn.diary1905.MainActivity.onCreate(MainActivity.java:64)
at android.app.Activity.performCreate(Activity.java:5990)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1106)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2278)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2387)
at android.app.ActivityThread.access$800(ActivityThread.java:151)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1303)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5254)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)
答案 0 :(得分：0)
编辑：我发现您的适配器存在许多问题：
DataProvider正在做什么。我不是那种模式的粉丝，但我敢打赌你的编译器抱怨因为你有 public class ListDataAdapter extends ArrayAdapter {
而不是
public class ListDataAdapter extends ArrayAdapter<?> {
甚至
public class ListDataAdapter extends ArrayAdapter<Object> {
ArrayAdapter已有自己的内部列表，因此您不需要拥有自己的List字段，甚至可以覆盖getView()以外的任何方法，甚至是构造函数。如果您要使用所有这些方法，也可以扩展BaseAdapter。我建议取出List定义，构造函数和除getView()以外的所有覆盖。
您正在notifyDataSetChanged()中呼叫getView()。 notifyDataSetChanged()仅在列表实际更改时才会被调用。例如，它在super.add()方法中调用，这可能足以触发ListView的刷新。但它在getView()内部没有任何结果，你应该把它拿出来。
从这些更改开始并发布结果。如果您的DataProvider课程没有任何错误，那么您应该处于更好的状态。
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.database.Cursor com.ulsteruniversity.eamonn.diary1905.DbHelper.getUpcomingAssignment(android.database.sqlite.SQLiteDatabase)' on a null object reference
问题不在于您的方法，问题是您尚未初始化运行该方法的DBHelper实例。
答案 1 :(得分：0)
//My query to return a cursor with the selected assignments
public Cursor getUpcomingAssignment(SQLiteDatabase sqLiteDatabase){
String sql = "SELECT * FROM " + TABLE_NAME_ASSIGNMENT + " WHERE "+ DUE_DATE + " <= date('now','+7 days') AND date('now')";
Cursor mycursor = sqLiteDatabase.rawQuery(sql, null);
Log.e("Database Operations","Method getUpComingAssignment called ");
return mycursor;
}
知道了！