Android 数据库管理— — —删除数据

package com.example.datebasetest;

import android.content.ContentValues;
import android.database.sqlite.SQLiteDatabase;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.Toast;

public class MainActivity extends AppCompatActivity {

    private Button btn;
    private DatabaseHelper dbHelper;
    private Button addButton;
    private Button updateData;
    private Button deleteData;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        btn = (Button)findViewById(R.id.create_database);
        dbHelper = new DatabaseHelper(this,"BookStore.db",null,2);
        addButton = (Button)findViewById(R.id.add_data);
        updateData = (Button)findViewById(R.id.update_data);
        deleteData = (Button)findViewById(R.id.delete_data);

        btn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                dbHelper.getWritableDatabase();
            }
        });

        addButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                SQLiteDatabase db = dbHelper.getWritableDatabase();
                ContentValues values = new ContentValues();
                values.put("name","wz");
                values.put("author","xx");
                values.put("price",1.0);
                values.put("pages",156);
                db.insert("Book",null,values);
                values.clear();
                values.put("name","wz2");
                values.put("author","xx2");
                values.put("price",2.0);
                values.put("pages",122);
                db.insert("Book",null,values);


            }
        });

        updateData.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                SQLiteDatabase db = dbHelper.getWritableDatabase();
                ContentValues values = new ContentValues();
                values.put("price",10.99);
                db.update("Book", values, "name=?", new String[]{"wz"});
            }
        });

        deleteData.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                SQLiteDatabase db = dbHelper.getWritableDatabase();
db.delete("Book","pages > ?", new String[]{"120"});
                Toast.makeText(MainActivity.this,"删除成功",Toast.LENGTH_SHORT).show();
            }
        });
    }
}