Android 从数据库显示listview时出错
我试图显示数据库中的listview项。但我的应用程序不断崩溃。我用我过去的项目代码来指导我,但仍然没有运气 Module.javaAndroid 从数据库显示listview时出错,android,database,sqlite,android-listview,Android,Database,Sqlite,Android Listview,我试图显示数据库中的listview项。但我的应用程序不断崩溃。我用我过去的项目代码来指导我,但仍然没有运气 Module.java @Override protected void onResume() { super.onResume(); ArrayList<String> labels = new ArrayList<String>(); ListView lstDine = (ListView) this.findViewById(R.
@Override
protected void onResume() {
super.onResume();
ArrayList<String> labels = new ArrayList<String>();
ListView lstDine = (ListView) this.findViewById(R.id.lst_module);
dbhelper.onCreate(null);
Cursor dinners = (Cursor) dbhelper.getAllLabels();
dinners.close();
lstDine.setAdapter(new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, labels));
lstDine.setOnItemClickListener(this);
}
public class DBHelper extends SQLiteOpenHelper {
// Database Version
private static final int DATABASE_VERSION = 1;
// Database Name
private static final String DATABASE_NAME = "spinnerExample";
// Labels table name
private static final String TABLE_LABELS = "labels";
// Labels Table Columns names
private static final String KEY_ID = "id";
private static final String KEY_NAME = "name";
public DBHelper(Context context) {
super(context, DATABASE_NAME, null, DATABASE_VERSION);
}
// Creating Tables
@Override
public void onCreate(SQLiteDatabase db) {
// Category table create query
String CREATE_CATEGORIES_TABLE = "CREATE TABLE " + TABLE_LABELS + "("
+ KEY_ID + " INTEGER PRIMARY KEY," + KEY_NAME + " TEXT)";
db.execSQL(CREATE_CATEGORIES_TABLE);
}
// Upgrading database
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
// Drop older table if existed
db.execSQL("DROP TABLE IF EXISTS " + TABLE_LABELS);
// Create tables again
onCreate(db);
}
/**
* Inserting new lable into lables table
* */
public void insertLabel(String label){
SQLiteDatabase db = this.getWritableDatabase();
ContentValues values = new ContentValues();
values.put(KEY_NAME, label);
// Inserting Row
db.insert(TABLE_LABELS, null, values);
db.close(); // Closing database connection
}
/**
* Removing label
* */
public void removeLabel(String label){
SQLiteDatabase db = this.getWritableDatabase();
ContentValues values = new ContentValues();
values.put(KEY_NAME, label);
// Removing Row
db.delete(TABLE_LABELS, KEY_NAME + "=?", new String[] {label});
db.close(); // Closing database connection
}
/**
* Getting all labels
* returns list of labels
* */
public List<String> getAllLabels(){
List<String> labels = new ArrayList<String>();
// Select All Query
String selectQuery = "SELECT * FROM " + TABLE_LABELS;
SQLiteDatabase db = this.getReadableDatabase();
Cursor cursor = db.rawQuery(selectQuery, null);
// looping through all rows and adding to list
if (cursor.moveToFirst()) {
do {
labels.add(cursor.getString(1));
} while (cursor.moveToNext());
}
// closing connection
cursor.close();
db.close();
// returning lables
return labels;
}
}
我不确定哪一部分出了问题。谢谢你的帮助。如果你能帮我编辑代码,我将不胜感激。我已经有好几次头痛了。由于这个原因,我无法进入下一部分
dbhelper.onCreate(null);
在上一行中,您传递的是空引用,因此您得到的是
原因:
java.lang.NullPointerException
07-25 08:36:42.937: E/AndroidRuntime(463): at sg.edu.tp.iit.mns.DBHelper.onCreate(DBHelper.java:36)
您可以传递DBHelper类对象
dbhelper.onCreate(dbhelper);
在上一行中,您传递的是空引用,因此您得到的是
原因:
java.lang.NullPointerException
07-25 08:36:42.937: E/AndroidRuntime(463): at sg.edu.tp.iit.mns.DBHelper.onCreate(DBHelper.java:36)
您可以传递DBHelper类对象
dbhelper.onCreate(dbhelper);
首先,您应该打开数据库-您将从数据库中获得数据:
db=openOrCreateDatabase(DATABASE_NAME, MODE_WORLD_WRITEABLE, null);
首先,您应该打开数据库-您将从数据库中获得数据:
db=openOrCreateDatabase(DATABASE_NAME, MODE_WORLD_WRITEABLE, null);
为什么要调用dbhelper.onCreate(null)?为什么要调用dbhelper.onCreate(null)?他正在实现SQLiteOpenHelper。在这种情况下,不需要自己打开数据库。他正在实现SQLiteOpenHelper。在这种情况下,不需要自己打开数据库。