DrySister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~

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);
 }
 }
}

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！