12.4 DrySister看妹子应用(第一版)——4.添加数据缓存(加入SQLite)

1.一些BB

上节我们为DrySister编写了一个异步图片加载缓存框架——SisterLoader(妹子加载器) 成功的从网络加载的图片缓存到了磁盘和内存中，当我们断开网络后，仍然能够查看这些图片， 但是，细心的你可能发现了一个很尴尬的地方，我们在有网的情况下进入APP，获取到图片相关 的信息，比如URL，如果退出了，断网，然后进来，图片就加载不出来了，图片已经缓存了，但是 我们没有图片对应的URL，就显得有些鸡肋了。所以我们需要对后台接口返回的数据进行存储， 当每次加载的时候，把返回的数据信息存储到本地，然后当无网的时候，可以让他加载本地 数据！所以本节我们为DrySister添加SQLite用于存储相关数据。任务都说清楚了，搞起~

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2.开始编写程序

在develop上开辟一个新的db分支，来完成本节相关代码的编写。

首先，我们添加一个用来判断网络状态的工具类：NetworkUtils.java， 就一个简单的判断网络是否可用的方法~这里我们还需要在AndroidManifest.xml 里加一个权限：android.permission.ACCESSNETWORKSTATE"的权限！

public class NetworkUtils {

    /** 获取网络信息 */

    private static NetworkInfo getActiveNetworkInfo(Context context) {

        ConnectivityManager cm = (ConnectivityManager) context

                .getSystemService(Context.CONNECTIVITY_SERVICE);

        return cm.getActiveNetworkInfo();

    }

    

    /** 判断网络是否可用 */

    public static boolean isAvailable(Context context) {

        NetworkInfo info = getActiveNetworkInfo(context);

        return info != null && info.isAvailable();

    }

}

接着定义一个数据库字段常量的类：TableDefine.java， 在里面把数据库名，字段写上：

public class TableDefine {

    public static final String TABLE_FULI = "fuli";

    public static final String COLUMN_ID = "id";

    public static final String COLUMN_FULI_ID = "_id";

    public static final String COLUMN_FULI_CREATEAT = "createAt";

    public static final String COLUMN_FULI_DESC = "desc";

    public static final String COLUMN_FULI_PUBLISHEDAT = "publishedAt";

    public static final String COLUMN_FULI_SOURCE = "source";

    public static final String COLUMN_FULI_TYPE = "type";

    public static final String COLUMN_FULI_URL = "url";

    public static final String COLUMN_FULI_USED = "used";

    public static final String COLUMN_FULI_WHO = "who";

}

再接着编写数据库的创建类：SisterOpenHelper.java，在里面完成数据库的创建

public class SisterOpenHelper extends SQLiteOpenHelper{



    private static final String DB_NAME = "sister.db";  //数据库名

    private static final int DB_VERSION = 1;    //数据库版本号



    public SisterOpenHelper(Context context) {

        super(context, DB_NAME, null, DB_VERSION);

    }



    @Override

    public void onCreate(SQLiteDatabase db) {

        String createTableSql = "CREATE TABLE IF NOT EXISTS " + TableDefine.TABLE_FULI + " ("

                + TableDefine.COLUMN_ID + " INTEGER PRIMARY KEY AUTOINCREMENT, "

                + TableDefine.COLUMN_FULI_ID + " TEXT, "

                + TableDefine.COLUMN_FULI_CREATEAT + " TEXT, "

                + TableDefine.COLUMN_FULI_DESC + " TEXT, "

                + TableDefine.COLUMN_FULI_PUBLISHEDAT + " TEXT, "

                + TableDefine.COLUMN_FULI_SOURCE + " TEXT, "

                + TableDefine.COLUMN_FULI_TYPE + " TEXT, "

                + TableDefine.COLUMN_FULI_URL + " TEXT, "

                + TableDefine.COLUMN_FULI_USED + " BOOLEAN, "

                + TableDefine.COLUMN_FULI_WHO + " TEXT"

                + ")";

        db.execSQL(createTableSql);

    }



    @Override

    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) { }

}

再接着，我们需要编写一个数据库的操作类，就是做增删改查，分页查询等操作的类， 这里我们把这个类写成单例的：SisterDBHelper.java，里面的编写的方法有这些：

具体代码：

public class SisterDBHelper {



    private static final String TAG = "SisterDBHelper";



    private static SisterDBHelper dbHelper;

    private SisterOpenHelper sqlHelper;

    private SQLiteDatabase db;



    private SisterDBHelper() {

        sqlHelper = new SisterOpenHelper(DrySisterApp.getContext());

    }



    /** 单例 */

    public static SisterDBHelper getInstance() {

        if(dbHelper == null) {

            synchronized (SisterDBHelper.class) {

                if(dbHelper == null) {

                    dbHelper = new SisterDBHelper();

                }

            }

        }

        return dbHelper;

    }



    /** 插入一个妹子 */

    public void insertSister(Sister sister) {

        db = getWritableDB();

        ContentValues contentValues = new ContentValues();

        contentValues.put(TableDefine.COLUMN_FULI_ID,sister.get_id());

        contentValues.put(TableDefine.COLUMN_FULI_CREATEAT,sister.getCreateAt());

        contentValues.put(TableDefine.COLUMN_FULI_DESC,sister.getDesc());

        contentValues.put(TableDefine.COLUMN_FULI_PUBLISHEDAT,sister.getPublishedAt());

        contentValues.put(TableDefine.COLUMN_FULI_SOURCE,sister.getSource());

        contentValues.put(TableDefine.COLUMN_FULI_TYPE,sister.getType());

        contentValues.put(TableDefine.COLUMN_FULI_URL,sister.getUrl());

        contentValues.put(TableDefine.COLUMN_FULI_USED,sister.getUsed());

        contentValues.put(TableDefine.COLUMN_FULI_WHO,sister.getWho());

        db.insert(TableDefine.TABLE_FULI,null,contentValues);

        closeIO(null);

    }



    /** 插入一堆妹子(使用事务) */

    public void insertSisters(ArrayList<Sister> sisters) {

        db = getWritableDB();

        db.beginTransaction();

        try{

            for (Sister sister: sisters) {

                ContentValues contentValues = new ContentValues();

                contentValues.put(TableDefine.COLUMN_FULI_ID,sister.get_id());

                contentValues.put(TableDefine.COLUMN_FULI_CREATEAT,sister.getCreateAt());

                contentValues.put(TableDefine.COLUMN_FULI_DESC,sister.getDesc());

                contentValues.put(TableDefine.COLUMN_FULI_PUBLISHEDAT,sister.getPublishedAt());

                contentValues.put(TableDefine.COLUMN_FULI_SOURCE,sister.getSource());

                contentValues.put(TableDefine.COLUMN_FULI_TYPE,sister.getType());

                contentValues.put(TableDefine.COLUMN_FULI_URL,sister.getUrl());

                contentValues.put(TableDefine.COLUMN_FULI_USED,sister.getUsed());

                contentValues.put(TableDefine.COLUMN_FULI_WHO,sister.getWho());

                db.insert(TableDefine.TABLE_FULI,null,contentValues);

            }

            db.setTransactionSuccessful();

        } finally {

            if(db != null && db.isOpen()) {

                db.endTransaction();

                closeIO(null);

            }

        }

    }



    /** 删除妹子(根据_id) */

    public void deleteSister(String _id) {

        db = getWritableDB();

        db.delete(TableDefine.TABLE_FULI,"_id =?",new String[]{_id});

        closeIO(null);

    }



    /** 删除所有妹子 */

    public void deleteAllSisters() {

        db = getWritableDB();

        db.delete(TableDefine.TABLE_FULI,null,null);

        closeIO(null);

    }



    /** 更新妹子信息(根据_id) */

    public void deleteSister(String _id,Sister sister) {

        db = getWritableDB();

        ContentValues contentValues = new ContentValues();

        contentValues.put(TableDefine.COLUMN_FULI_ID,sister.get_id());

        contentValues.put(TableDefine.COLUMN_FULI_CREATEAT,sister.getCreateAt());

        contentValues.put(TableDefine.COLUMN_FULI_DESC,sister.getDesc());

        contentValues.put(TableDefine.COLUMN_FULI_PUBLISHEDAT,sister.getPublishedAt());

        contentValues.put(TableDefine.COLUMN_FULI_SOURCE,sister.getSource());

        contentValues.put(TableDefine.COLUMN_FULI_TYPE,sister.getType());

        contentValues.put(TableDefine.COLUMN_FULI_URL,sister.getUrl());

        contentValues.put(TableDefine.COLUMN_FULI_USED,sister.getUsed());

        contentValues.put(TableDefine.COLUMN_FULI_WHO,sister.getWho());

        db.update(TableDefine.TABLE_FULI,contentValues,"_id =?",new String[]{_id});

        closeIO(null);

    }



    /** 查询当前表中有多少个妹子 */

    public int getSistersCount() {

        db = getReadableDB();

        Cursor cursor = db.rawQuery("SELECT COUNT (*) FROM " + TableDefine.TABLE_FULI,null);

        cursor.moveToFirst();

        int count = cursor.getInt(0);

        Log.v(TAG,"count：" + count);

        closeIO(cursor);

        return count;

    }



    /** 分页查询妹子，参数为当前页和每一个的数量，页数从0开始算 */

    public List<Sister> getSistersLimit(int curPage,int limit) {

        db =  getReadableDB();

        List<Sister> sisters = new ArrayList<>();

        String startPos = String.valueOf(curPage * limit);  //数据开始位置

        if(db != null) {

            Cursor cursor = db.query(TableDefine.TABLE_FULI,new String[] {

                    TableDefine.COLUMN_FULI_ID, TableDefine.COLUMN_FULI_CREATEAT,

                    TableDefine.COLUMN_FULI_DESC, TableDefine.COLUMN_FULI_PUBLISHEDAT,

                    TableDefine.COLUMN_FULI_SOURCE, TableDefine.COLUMN_FULI_TYPE,

                    TableDefine.COLUMN_FULI_URL, TableDefine.COLUMN_FULI_USED,

                    TableDefine.COLUMN_FULI_WHO,

            },null,null,null,null,TableDefine.COLUMN_ID,startPos + "," + limit);

            while (cursor.moveToNext()) {

                Sister sister = new Sister();

                sister.set_id(cursor.getString(cursor.getColumnIndex(TableDefine.COLUMN_FULI_ID)));

                sister.setCreateAt(cursor.getString(cursor.getColumnIndex(TableDefine.COLUMN_FULI_CREATEAT)));

                sister.setDesc(cursor.getString(cursor.getColumnIndex(TableDefine.COLUMN_FULI_DESC)));

                sister.setPublishedAt(cursor.getString(cursor.getColumnIndex(TableDefine.COLUMN_FULI_PUBLISHEDAT)));

                sister.setSource(cursor.getString(cursor.getColumnIndex(TableDefine.COLUMN_FULI_SOURCE)));

                sister.setType(cursor.getString(cursor.getColumnIndex(TableDefine.COLUMN_FULI_TYPE)));

                sister.setUrl(cursor.getString(cursor.getColumnIndex(TableDefine.COLUMN_FULI_URL)));

                sister.setUsed(cursor.getInt(cursor.getColumnIndex(TableDefine.COLUMN_FULI_USED)));

                sisters.add(sister);

            }

            closeIO(cursor);

        }

        return sisters;

    }



    /** 查询所有妹子 */

    public List<Sister> getAllSisters() {

        db = getReadableDB();

        List<Sister> sisters = new ArrayList<>();

        Cursor cursor = db.rawQuery("SELECT * FROM "+TableDefine.TABLE_FULI,null);

        cursor.moveToFirst();

        while (cursor.moveToNext()) {

            Sister sister = new Sister();

            sister.set_id(cursor.getString(cursor.getColumnIndex(TableDefine.COLUMN_FULI_ID)));

            sister.setCreateAt(cursor.getString(cursor.getColumnIndex(TableDefine.COLUMN_FULI_CREATEAT)));

            sister.setDesc(cursor.getString(cursor.getColumnIndex(TableDefine.COLUMN_FULI_DESC)));

            sister.setPublishedAt(cursor.getString(cursor.getColumnIndex(TableDefine.COLUMN_FULI_PUBLISHEDAT)));

            sister.setSource(cursor.getString(cursor.getColumnIndex(TableDefine.COLUMN_FULI_SOURCE)));

            sister.setType(cursor.getString(cursor.getColumnIndex(TableDefine.COLUMN_FULI_TYPE)));

            sister.setUrl(cursor.getString(cursor.getColumnIndex(TableDefine.COLUMN_FULI_URL)));

            sister.setUsed(cursor.getInt(cursor.getColumnIndex(TableDefine.COLUMN_FULI_USED)));

            sisters.add(sister);

        }

        closeIO(cursor);

        return sisters;

    }



    /** 获得可写数据库的方法 */

    private SQLiteDatabase getWritableDB() {

        return sqlHelper.getWritableDatabase();

    }



    /** 获得可读数据库的方法 */

    private SQLiteDatabase getReadableDB() {

        return sqlHelper.getReadableDatabase();

    }



    /** 关闭cursor和数据库的方法 */

    private void closeIO(Cursor cursor) {

        if(cursor != null) {

            cursor.close();

        }

        if(db != null) {

            db.close();

        }

    }



}

嗯，还是蛮简单的，都是一些SQLite的方法调用而已，接着我们对布局做一下更改， 把activity_main.xml改成下面的代码，就是换成上一个和下一个这样：

<?xml version="1.0" encoding="utf-8"?>

<RelativeLayout

    xmlns:android="http://schemas.android.com/apk/res/android"

    android:layout_width="match_parent"

    android:layout_height="match_parent">



    <Button

        android:id="@+id/btn_previous"

        android:layout_width="wrap_content"

        android:layout_height="wrap_content"

        android:layout_alignParentBottom="true"

        android:visibility="invisible"

        android:text="上一个"/>



    <Button

        android:id="@+id/btn_next"

        android:layout_width="wrap_content"

        android:layout_height="wrap_content"

        android:layout_alignParentBottom="true"

        android:layout_toRightOf="@id/btn_previous"

        android:text="下一个"/>



    <ImageView

        android:id="@+id/img_show"

        android:layout_width="wrap_content"

        android:layout_height="wrap_content"

        android:layout_above="@+id/btn_previous"/>



</RelativeLayout>

最后就是对MainActivity.java的一些逻辑更改了，核心的要点如下：

• 1.curPos和page的控制以及处理逻辑
• 2.根据网络是否可用加载网络还是数据库数据
• 3.加载网络数据时存储到数据库需要避免重复插入 等等。

代码实现：

public class MainActivity extends AppCompatActivity implements View.OnClickListener {

    private Button previousBtn;

    private Button nextBtn;

    private ImageView showImg;



    private ArrayList<Sister> data;

    private int curPos = 0; //当前显示的是哪一张

    private int page = 1;   //当前页数

    private PictureLoader loader;

    private SisterApi sisterApi;

    private SisterTask sisterTask;

    private SisterLoader mLoader;

    private SisterDBHelper mDbHelper;



    @Override

    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_main);

        sisterApi = new SisterApi();

        loader = new PictureLoader();

        mLoader = SisterLoader.getInstance(MainActivity.this);

        mDbHelper = SisterDBHelper.getInstance();

        initData();

        initUI();

    }



    private void initData() {

        data = new ArrayList<>();

        sisterTask = new SisterTask();

        sisterTask.execute();

    }



    private void initUI() {

        previousBtn = (Button) findViewById(R.id.btn_previous);

        nextBtn = (Button) findViewById(R.id.btn_next);

        showImg = (ImageView) findViewById(R.id.img_show);



        previousBtn.setOnClickListener(this);

        nextBtn.setOnClickListener(this);

    }



    @Override

    public void onClick(View v) {

        switch (v.getId()) {

            case R.id.btn_previous:

                --curPos;

                if (curPos == 0) {

                    previousBtn.setVisibility(View.INVISIBLE);

                }

                if (curPos == data.size() - 1) {

                    sisterTask = new SisterTask();

                    sisterTask.execute();

                } else if(curPos < data.size()) {

                    mLoader.bindBitmap(data.get(curPos).getUrl(), showImg, 400, 400);

                }

                break;

            case R.id.btn_next:

                previousBtn.setVisibility(View.VISIBLE);

                if(curPos < data.size()) {

                    ++curPos;

                }

                if (curPos > data.size() - 1) {

                    sisterTask = new SisterTask();

                    sisterTask.execute();

                } else if(curPos < data.size()){

                    mLoader.bindBitmap(data.get(curPos).getUrl(), showImg, 400, 400);

                }

                break;

        }

    }



    private class SisterTask extends AsyncTask<Void, Void, ArrayList<Sister>> {



        public SisterTask() {

        }



        @Override

        protected ArrayList<Sister> doInBackground(Void... params) {

            ArrayList<Sister> result = new ArrayList<>();

            if (page < (curPos + 1) / 10 + 1) {

                ++page;

            }

            //判断是否有网络

            if (NetworkUtils.isAvailable(getApplicationContext())) {

                result = sisterApi.fetchSister(10, page);

                //查询数据库里有多少个妹子，避免重复插入

                if(mDbHelper.getSistersCount() / 10 < page) {

                    mDbHelper.insertSisters(result);

                }

            } else {

                result.clear();

                result.addAll(mDbHelper.getSistersLimit(page - 1, 10));

            }

            return result;

        }



        @Override

        protected void onPostExecute(ArrayList<Sister> sisters) {

            super.onPostExecute(sisters);

            data.addAll(sisters);

            if (data.size() > 0 && curPos + 1 < data.size()) {

                mLoader.bindBitmap(data.get(curPos).getUrl(), showImg, 400, 400);

            }

        }



        @Override

        protected void onCancelled() {

            super.onCancelled();

            sisterTask = null;

        }

    }





    @Override

    protected void onDestroy() {

        super.onDestroy();

        if (sisterTask != null) {

            sisterTask.cancel(true);

        }

    }

}

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3.运行效果图

操作步骤：

把项目跑起来后，一直按下一页下一页缓存一堆图片，接着断开网络，进入DrySister， Duang~，神奇的发现，有妹子出现了，按下一页或者上一页也可以切换图片，妈妈再也 不用担心我在没网的时候不可以看DrySister了！

运行截图：

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4.小结

好的，本节在上节的基础上行添加了SQlite保存后台数据，当无网的时候也可以查看 妹子图片，代码的大的改动如上述，还有一些小改，具体看代码。 最后把db分支的代码合并到develop分支上，然后删除db分支，把更新后的 develop分支推送到Github！

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代码下载：

https://github.com/coder-pig/DrySister/tree/develop 欢迎follow，star，觉得有什么想加进来的可以提下issues！