SQLite-SQLiteDatabase 数据库实例练习

今天趁着有时间，自己在网上找了相关的数据库操作代码，进行了一下练习，先上代码

main.xml文件

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="com.example.sqlittest.MainActivity" >

    <TextView
        android:id="@+id/tv"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/hello_world"
        android:textColor="#0000ff" />

    <LinearLayout
        android:id="@+id/l1"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_alignParentBottom="true"
        android:orientation="horizontal" >

        <Button
            android:id="@+id/bt1"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="创建数库"
            android:textColor="#0000ff" />

        <Button
            android:id="@+id/bt2"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="创建表格"
            android:textColor="#0000ff" />

        <Button
            android:id="@+id/bt3"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="插入数据"
            android:textColor="#0000ff" />
        </LinearLayout>
<LinearLayout
     android:id="@+id/l2"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"

        android:layout_above="@id/l1"
        android:orientation="horizontal" >
    >
        <Button
            android:id="@+id/bt4"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="删除数据"
            android:textColor="#0000ff" />

        <Button
            android:id="@+id/bt5"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="修改数据"
            android:textColor="#0000ff" />

        <Button
            android:id="@+id/bt6"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="查看表格"
            android:textColor="#0000ff" />
    </LinearLayout>

</RelativeLayout>

然后看练习代码

package com.example.sqlittest;

import android.R.string;
import android.support.v4.widget.SimpleCursorAdapter.ViewBinder;
import android.support.v7.app.ActionBarActivity;
import android.content.ContentValues;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.os.Bundle;
import android.util.Log;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.TextView;

public class MainActivity extends ActionBarActivity implements OnClickListener {
    TextView tv;
    Button bt1, bt2, bt3, bt4, bt5, bt6, bt7;
    SQLiteDatabase mDatabase;

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

        mDatabase = SQLiteDatabase.openOrCreateDatabase(
                "/data/data/com.example.sqlittest/test.db", null);

        initButton();

    }

    private void initButton() {
        tv = (TextView) findViewById(R.id.tv);
        bt1 = (Button) findViewById(R.id.bt1);
        bt2 = (Button) findViewById(R.id.bt2);
        bt3 = (Button) findViewById(R.id.bt3);
        bt4 = (Button) findViewById(R.id.bt4);
        bt5 = (Button) findViewById(R.id.bt5);
        bt6 = (Button) findViewById(R.id.bt6);
        bt1.setOnClickListener(this);
        bt2.setOnClickListener(this);
        bt3.setOnClickListener(this);
        bt4.setOnClickListener(this);
        bt5.setOnClickListener(this);
        bt6.setOnClickListener(this);

    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();
        if (id == R.id.action_settings) {
            return true;
        }
        return super.onOptionsItemSelected(item);
    }

    // 创建数据库
    private void createdb() {
        mDatabase = SQLiteDatabase.openOrCreateDatabase(
                "/data/data/com.example.sqlittest/test.db", null);

    }

    // 创建表格
    private void createtabe() {
        String stu_table = "create table testtable(_id integer primary key autoincrement,sname text,snumber text)";
        mDatabase.execSQL(stu_table);

    }

    // 插入数据方式1
    private void insert1() {
        ContentValues contentValues = new ContentValues();
        contentValues.put("sname", "zhangsan");
        contentValues.put("snumber", "13166111082");
        mDatabase.insert("testtable", null, contentValues);

    }

    // 插入数据方式2
    private void insert2() {
        String stu_sql = "insert into testtable(sname,snumber) values('xiaoming','01005')";
        mDatabase.execSQL(stu_sql);

    }

    // 删除数据方式1
    private void delete1() {
        String string = "_id=?";
        String[] string2 = { String.valueOf(1) };
        mDatabase.delete("testtable", string, string2);
    }

    // 删除数据方式2
    private void delete2() {
        String sql = "delete from testtable where _id = 2";
        mDatabase.execSQL(sql);

    }

    // 修改数据方式1
    private void change1() {
        String string = "_id=?";
        String[] string2 = { String.valueOf(1) };
        ContentValues contentValues = new ContentValues();
        contentValues.put("sname", "zhangsi");
        mDatabase.update("testtable", contentValues, string, string2);

    }

    // 修改数据方式2
    private void change2() {
        String sql = "update testtable set snumber = 654321 where _id = 1";
        mDatabase.execSQL(sql);

    }

    // 数据库查询
    private String squre() {
        StringBuffer stringBuffer = new StringBuffer();
        Cursor cursor = mDatabase.query("testtable", null, null, null, null,
                null, null);
        // 判断游标是否为空
        if (!cursor.moveToFirst()) {
            return null;
        }
        for (int i = 0; i < cursor.getCount() - 1; i++) {
            // 获得ID
            cursor.moveToNext();
            int id = cursor.getInt(0);
            // 获得用户名
            int name_id = cursor.getColumnIndexOrThrow("sname");
            String username = cursor.getString(name_id);
            // 获得密码
            int number_id = cursor.getColumnIndexOrThrow("snumber");
            Log.e("123",
                    "" + name_id + " " + number_id + " count"
                            + cursor.getCount());
            String password = cursor.getString(number_id);
            stringBuffer.append("name_id:" + name_id + "\n" + " name:"
                    + username + "\n" + " number:" + password + "\n");

        }

        return stringBuffer.toString();
    }

    @Override
    public void onClick(View arg0) {
        // TODO Auto-generated method stub
        switch (arg0.getId()) {
        case R.id.bt1:
            // createdb();
            break;
        case R.id.bt2:
            // createtabe();
            break;
        case R.id.bt3:
            insert1();
            insert2();
            break;
        case R.id.bt4:
            delete1();
            delete2();
            break;
        case R.id.bt5:
            change1();
            change2();
            break;
        case R.id.bt6:
            tv.setText(squre());
            break;
        default:
            break;
        }
    }
}

结果如下

在做练习的时候，遇到了以下几个问题：

1）当创建数据库的时候，刚开始使用的是

mDatabase = SQLiteDatabase.openOrCreateDatabase("test.db",null);

结果报错了。所以我们可以得出的结论是，这个数据库创建，必须是指定的应用路径

2）当进行遍历的时候，开始使用的是

for (int i = 0; i < cursor.getCount() - 1; i++) {
    cursor.move(i);
}

报错，后来发现问题了，原来是数据库并不会自动更新id，也就是说，如果你删除了id=3的行，那么这一行就永久消失了，id只会增加，不会自动重新排序

3）当我们删除一个数据的时候，我们查看数据库，会发现表格内容如下

|zhangsan|
|xiaoming|
|zhangsan|
|xiaoming|
|zhangsan|
|xiaoming|
|zhangsan|
|xiaoming|
|zhangsan|
|xiaoming|
|zhangsan|
|xiaoming|
|zhangsan|
|xiaoming|
|zhangsan|
|xiaoming|
|zhangsan|
|xiaoming|
|zhangsan|
|xiaoming|
|zhangsan|
|xiaoming|
|zhangsan|

另外，数据库id永远是从1开始，而不是0，这是问题2报错的原因