SQLite—homework

主要的界面布局：

 <EditText
        android:id="@+id/edt"
        android:textSize="20dp"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"/>
    <LinearLayout
            android:orientation="horizontal"
            android:layout_width="match_parent"
            android:layout_height="wrap_content">
        <Button
            android:id="@+id/add"
            android:textSize="10sp"
            android:layout_width="0dp"
            android:layout_weight="1"
            android:onClick="onClick"
            android:layout_height="wrap_content"
            android:text="增加一条新记录"/>
        <Button
            android:id="@+id/delete"
            android:textSize="10sp"
            android:layout_width="0dp"
            android:layout_weight="1"
            android:onClick="onClick"
            android:layout_height="wrap_content"
            android:text="删除第一条记录"/>
    </LinearLayout>
        <ListView
            android:id="@+id/list_item"
            android:layout_width="match_parent"
            android:layout_height="wrap_content">

              

第二个布局：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent">
    <TextView
        android:textSize="20dp"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/tv_list"/>

</LinearLayout>
首先要进行数据库表的创建：
跟之前的一样  只是没那么复杂

public class MyDBHelper extends SQLiteOpenHelper {
    private String sql = "create table student(_id integer primary key autoincrement," + "name text not null," +
            "classmate text not null,"+"age integer)";


    public MyDBHelper(Context context) {
        super(context, "studentInfo", null, 1);

    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        db.execSQL(sql);
    }


    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        db.execSQL("drop table if exists student");
        onCreate(db);
    }
}

DAO部分：

public class DAO {
    private MyDBHelper dbHelper;
    private SQLiteDatabase sqLiteDatabase;

    public DAO(Context context){
        dbHelper = new MyDBHelper(context);
    }
    //向数据库中插入数据
    public void insert(String name){
        sqLiteDatabase = dbHelper.getWritableDatabase();
        String sql = "insert into person(name) values('"+name+"')";
        sqLiteDatabase.execSQL(sql);
    }

    public Cursor selectAll() {
        sqLiteDatabase = dbHelper.getReadableDatabase();
        Cursor cursor = sqLiteDatabase.query("person", null, null, null, null, null, null);
        return cursor;
    }

    public void delete(String id){
        sqLiteDatabase = dbHelper.getWritableDatabase();
        String sql = "delete from person where _id="+String.valueOf(id);//"delete from student where _id="+id
        sqLiteDatabase.execSQL(sql);
    }
}
Adapter部分：

public class MyCursorAdapter extends CursorAdapter {


        public MyCursorAdapter(Context context, Cursor cursor) {
            super(context, cursor, 0);
        }

        @Override
        public View newView(Context context, Cursor cursor, ViewGroup viewGroup) {
            return LayoutInflater.from(context).inflate(R.layout.listview_mian,viewGroup,false);
        }

        @Override
        public void bindView(View view, Context context, Cursor cursor) {
            TextView name = (TextView) view.findViewById(R.id.tv_list);
            name.setText(cursor.getString(cursor.getColumnIndex("name")));
        }
    }
MainActivity Java代码：

public class MainActivity extends AppCompatActivity {
    private EditText edt;
    private ListView listView;
    private MyCursorAdapter adapter;
    private DAO DAO;
    private Cursor cursor;
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        edt = (EditText)findViewById(R.id.edt);

        listView = (ListView)findViewById(R.id.list_item);
        DAO = new DAO(this);
        cursor = DAO.selectAll();
        if(cursor!=null){
            adapter = new MyCursorAdapter(MainActivity.this,cursor);
            listView.setAdapter(adapter);
        }


    }

    public void onClick(View view) {
        switch(view.getId()){
            case R.id.add:

                String name = edt.getText().toString();
                DAO.insert(name);
                cursor = DAO.selectAll();
                if(cursor!=null){
                    adapter = new MyCursorAdapter(this,cursor);
                    listView.setAdapter(adapter);
                }
                break;
            case R.id.delete:

                if(cursor!=null){
                    if(cursor.moveToFirst()){
                        DAO.delete(cursor.getString(cursor.getColumnIndex("_id")));
                        cursor = DAO.selectAll();
                    }
                }
                adapter = new MyCursorAdapter(this,cursor);
                listView.setAdapter(adapter);
                break;
        }

    }
}

但不幸的是 运行起来依然存在问题 。。。