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~
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="https://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); } }}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：
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！
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！