android sqlite的简单应用（创建，插入，更新，查找，删除等）

sqlite作为跨平台的一种小型数据库，进行数据储存查找还是蛮方便的，但是不熟悉SQL语句还是挺烦人的，先记录下来，看看以后用得上不。

数据的更新与保存：

 /**
     * 保存数据
     * */
    protected void saveDate(){
        SimpleDateFormat sDateFormat = new SimpleDateFormat(
                "yyyy年MM月dd日HH时mm分", Locale.getDefault());
        String date = sDateFormat.format(new java.util.Date());
        //创建文件夹
        File file = new File("/sdcard/TreadWear");
        boolean isDirectoryCreated=file.exists();
        if (!isDirectoryCreated) {
            isDirectoryCreated= file.mkdir();
        }
        if(isDirectoryCreated) {
            SQLiteDatabase db = SQLiteDatabase.openOrCreateDatabase("/sdcard/TreadWear/date.db",null);
            //创建一个表
            try {
                db.execSQL("create table wheel_date(" +
                        "WheelId varchar(50) NOT NULL primary key," +
                        "TreadWear varchar(50) NULL," +
                        "WheelThick varchar(50) NULL," +
                        "RimWidth varchar(50) NULL," +
                        "RimThick varchar(50) NULL," +
                        "Time varchar(50) NOT NULL,"+
                        "AllDate varchar(50) NOT NULL)");
            }catch (Exception e) {
                //This happens on every launch that isn't the first one.
                Log.w("一般第一次不发生的错误", "Error while creating db: " + e.toString());
            }
            /**
             * 更新插入数据
             * */
            try {
                db.execSQL("REPLACE INTO wheel_date VALUES('"+
                        getIntent().getStringExtra("wheel_date") +"','"+
                        temp[0] +"','"+
                        temp[1] +"','"+
                        temp[2] +"','"+
                        temp[3] +"','"+
                        date +"','1')");
            }catch (Exception e) {
                //This happens on every launch that isn't the first one.
                Log.w("一般不会发生的错误", "Error while REPLACE INTO db: " + e.toString());
            }
            Toast.makeText(DateActivity.this, "数据已保存", Toast.LENGTH_SHORT).show();
            db.close();
            finish();
            overridePendingTransition(0, R.anim.zoomout);
        }else {
            Toast.makeText(DateActivity.this, "保存数据失败", Toast.LENGTH_SHORT).show();
        }
    }

需要权限：

    <!--SD卡读写权限-->
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
    <uses-permission android:name="android.permission.CHANGE_NETWORK_STATE" />
    <uses-permission android:name="android.permission.CHANGE_WIFI_STATE"/>
    <!--在sdcard中创建/删除文件的权限 -->
    <uses-permission android:name="android.permission.MOUNT_UNMOUNT_FILESYSTEMS"/>

通过string进行查找数据：

//读取数据
            Cursor c = db.rawQuery("SELECT* FROM wheel_date WHERE WheelId = ?", new String[]{string});
            int i = 0;
            while (c.moveToNext()) {
                i++;
            }
            if(i == 0){
                Toast.makeText(SearchDateActivity.this, "无数据", Toast.LENGTH_SHORT).show();
            }else {
                c.moveToFirst();
                date_1.setText(c.getString(c.getColumnIndex("TreadWear")));
                date_2.setText(c.getString(c.getColumnIndex("WheelThick")));
                date_3.setText(c.getString(c.getColumnIndex("RimWidth")));
                date_4.setText(c.getString(c.getColumnIndex("RimThick")));
                date_5.setText(c.getString(c.getColumnIndex("Time")));
            }
            c.close();

删除数据库数据，一条代码就够了：

db.delete("wheel_date","WheelId = ?",new String[]{s_date});

然后需要注意的是记得关闭数据库，要写在返回键跟销毁里面。

主要就是对于SQL语句的不熟悉而记录，作为程序员，SQL语句应该是基础的基础，还是需要加强学习啊！