SQLite数据库增删改查

在安卓开发中不可避免的会遇到在手机中保存数据的时候，如果只是小量数据（如保存设置等）的话，用SharedPreferences是个极好的选择，它以键值对的形式保存数据，但是如果数据量比较多的话，比如一个键对应了一个集合的情况，此时再用SharedPreferences保存数据就显得吃力了，如果再需要对数据进行修改删除的操作，这个保存数据的方法明显不适合了，所以安卓本身也内置了sqlite数据库，对于保存app里面的数据已经够了。

新建安卓工程后新建一个类：SQLDatabase .java，该类继承自SQLiteOpenHelper，主要用于新建数据库，新建数据表和更新数据库：

public class SQLDatabase extends SQLiteOpenHelper{
    private Context context;
    private String CREAT_BOOK="create table Book(id integer primary key autoincrement,author text,price real,pages integer,name text)";
    public SQLDatabase(Context context, String name, SQLiteDatabase.CursorFactory factory, int version) {
        super(context, name, factory, version);
        this.context = context;
    }
    @Override
    public void onCreate(SQLiteDatabase db) {
        //建表
        db.execSQL(CREAT_BOOK);
        //插入一些数据
        Toast.makeText(context, "创建数据库成功", Toast.LENGTH_SHORT).show();
    }
    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        Toast.makeText(context, "数据库更新了", Toast.LENGTH_SHORT).show();
    }
}

布局文件：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/activity_main"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context="com.example.mydiyizho3_2.MainActivity">
<Button
    android:id="@+id/button1"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:onClick="onClick"
    android:text="增"/>
    <Button
        android:id="@+id/button2"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:onClick="onClick"
        android:text="删"/>
    <Button
        android:id="@+id/button3"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:onClick="onClick"
        android:text="改"/>
    <Button
        android:id="@+id/button4"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:onClick="onClick"
        android:text="查"/>

</LinearLayout>

接下来就是增加，删除，修改，查找数据：

public class MainActivity extends AppCompatActivity {

    private static final String TAG = "MainActivity";
    private SQLDatabase database;
    private SQLiteDatabase writableDatabase;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        database = new SQLDatabase(MainActivity.this, "BookStore.db", null, 1);
    }

    public void onClick(View view) {
        switch (view.getId()){
            case R.id.button1://增
                writableDatabase = database.getWritableDatabase();
                ContentValues values = new ContentValues();
                for (int i = 0; i <20 ; i++) {
                    values.put("author","homeng"+i);
                    values.put("price",10.5+i);
                    values.put("pages",1000+i);
                    values.put("name","杂技团"+i);
                    long book = writableDatabase.insert("Book", null, values);
                    Log.i(TAG,"每天的id="+book);
                }
                //关闭
                writableDatabase.close();
                break;
            case R.id.button2://删
                writableDatabase = database.getWritableDatabase();
                int book = writableDatabase.delete("Book", "id=?", new String[]{1 + ""});
                Log.i(TAG,"这是删除的"+book);
                writableDatabase.close();
                break;
            case R.id.button3://改
                writableDatabase = database.getWritableDatabase();
                ContentValues update = new ContentValues();
                update.put("price",10000);
                int update1 = writableDatabase.update("Book", update, "author=?", new String[]{"homeng5"});
                Log.i(TAG,"这是修改的"+update1);
                writableDatabase.close();
                break;
            case R.id.button4://查
                writableDatabase = database.getWritableDatabase();
                Cursor book1 = writableDatabase.query("Book", null, null, null, null, null, null);
                if (book1.moveToFirst()){
                    do {
                        String name = book1.getString(book1.getColumnIndex("name"));
                        float price = book1.getFloat(book1.getColumnIndex("price"));
                        int pages = book1.getInt(book1.getColumnIndex("pages"));
                        String author = book1.getString(book1.getColumnIndex("author"));
                        Log.i(TAG,"name"+name);
                        Log.i(TAG,"price"+price);
                        Log.i(TAG,"pages"+pages);
                        Log.i(TAG,"author"+author);
                    }while (book1.moveToNext());
                }
                writableDatabase.close();
                break;
        }
    }
}