android - 如何在 android 中创建和设置 List 以从 SQLite 检索数据？

Question

我正在尝试为地址簿制作一个列表，其中包括名字、姓氏等。在这种情况下，我想从 SQLite 中检索名字中的所有值并将其放入列表中。不是 SQLite 专家，但很努力却一无所获....出现空指针异常：/ 有人可以帮忙吗？公共类 List_fname 扩展 ListActivity {

public String [] list = get_name(); 

public String [] get_name(){
    int i = 0;
    String [] lista;
    lista = new String [100]; 
    DBAdapter db = new DBAdapter(this);
    db.open();
    Cursor c = db.getAllContacts();
    if (c.moveToFirst()) {
        do {

            lista[i] = c.getString(0);
            i++;

        } while (c.moveToNext());
    }
    db.close();
    return lista;

}

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

    //ArrayList<String> list = new ArrayList<String>();
    String [] listb = list;
    setListAdapter(new ArrayAdapter<String>(this,
            android.R.layout.simple_list_item_2, listb));

}}

Answer 1

要使用 SQLite DB，您可以从 SQLiteOpenHelper 扩展。这是第一步。类创建和使用 DB：

import android.content.ContentValues;
    import android.content.Context;
    import android.database.Cursor;
    import android.database.sqlite.SQLiteDatabase;
    import android.database.sqlite.SQLiteOpenHelper;
    import android.provider.BaseColumns;

public class DBHelper extends SQLiteOpenHelper {
public static interface CONTACT extends BaseColumns {
            String TABLE_NAME = "human";
            String FIRST_NAME = "first_name";
            String LAST_NAME = "last_name";
        }
private static final String CREATE_TABLE = "CREATE TABLE IF NOT EXISTS ";
        private static final String DATABASE_NAME = "someDataBase";
        private static final int DATABASE_VERSION = 1;
private static final String CREATE_TABLE_CONTACT = CREATE_TABLE + CONTACT.TABLE_NAME + " (" + CONTACT._ID
                + " INTEGER PRIMARY KEY," + CONTACT.FIRST_NAME + " TEXT, " + CONTACT.LAST_NAME + " TEXT);";
public DBHelper(Context context) {
            super(context, DATABASE_NAME, null, DATABASE_VERSION);
        }
@Override
        public void onCreate(SQLiteDatabase db) {
            db.execSQL(CREATE_TABLE_CONTACT);
        }
@Override
        public void onUpgrade(SQLiteDatabase db, int arg1, int arg2) {
            db.execSQL("DROP TABLE IF EXISTS " + CONTACT.TABLE_NAME);
            onCreate(db);
}
public Cursor getAllContacts() {
            return getReadableDatabase().query(CONTACT.TABLE_NAME, null, null, null, null, null, null);
        }
public void insertContact(String firstName, String lastName) {
            final ContentValues values = new ContentValues();
            values.put(CONTACT.FIRST_NAME, firstName);
            values.put(CONTACT.LAST_NAME, lastName);
            getWritableDatabase().insert(CONTACT.TABLE_NAME, null, values);
        }
    }

ListView 的简单布局：

xmlns:tools="http://schemas.android.com/tools"

android:layout_width="match_parent"

android:layout_height="match_parent"

安卓：方向=“垂直”>

<ListView
        android:id="@+id/testList" 
        android:layout_width="fill_parent" 
        android:layout_height="fill_parent" />

以及使用它的活动：

import java.util.Random;
    import android.app.Activity;
    import android.database.Cursor;
    import android.os.Bundle;
    import android.widget.ListView;
    import android.widget.SimpleCursorAdapter;
public class MainActivity extends Activity {
private DBHelper db;
@Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_main);
            db = new DBHelper(this);
//useless part to insert some data
            Random rand = new Random();
            for (int i = 0; i < 20; i++) {
                db.insertContact("" + i, "" + rand.nextInt(100));
            }
Cursor allContacts = db.getAllContacts();
            ListView testList = (ListView) findViewById(R.id.testList);
            testList.setAdapter(new SimpleCursorAdapter(this, android.R.layout.two_line_list_item, allContacts,
                    new String[] { DBHelper.CONTACT.FIRST_NAME, DBHelper.CONTACT.LAST_NAME }, new int[] {
                            android.R.id.text1, android.R.id.text2 }));
        }
    }