編輯：關於Android編程
???上節我們為DrySister編寫了一個異步圖片加載緩存框架——SisterLoader(妹子加載器)
成功的從網絡加載的圖片緩存到了磁盤和內存中，當我們斷開網絡後，仍然能夠查看這些圖片，但是，細心的你可能發現了一個很尴尬的地方，我們在有網的情況下進入APP，獲取到圖片相關的信息，比如URL，如果退出了，斷網，然後進來，圖片就加載不出來了，圖片已經緩存了，但是我們沒有圖片對應的URL，就顯得有些雞肋了。所以我們需要對後台接口返回的數據進行存儲，當每次加載的時候，把返回的數據信息存儲到本地，然後當無網的時候，可以讓他加載本地數據！所以本節我們為DrySister添加SQLite用於存儲相關數據。任務都說清楚了，搞起~
在develop上開辟一個新的db分支，來完成本節相關代碼的編寫。
首先，我們添加一個用來判斷網絡狀態的工具類：NetworkUtils.java，就一個簡單的判斷網絡是否可用的方法~這裡我們還需要在AndroidManifest.xml裡加一個權限：android.permission.ACCESS_NETWORK_STATE”的權限！
public class NetworkUtils {
/** 獲取網絡信息 */
private static NetworkInfo getActiveNetworkInfo(Context context) {
ConnectivityManager cm = (ConnectivityManager) context
.getSystemService(Context.CONNECTIVITY_SERVICE);
return cm.getActiveNetworkInfo();
}
/** 判斷網絡是否可用 */
public static boolean isAvailable(Context context) {
NetworkInfo info = getActiveNetworkInfo(context);
return info != null && info.isAvailable();
}
}
接著定義一個數據庫字段常量的類：TableDefine.java，
在裡面把數據庫名，字段寫上：
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";
}
再接著編寫數據庫的創建類：SisterOpenHelper.java，在裡面完成數據庫的創建
public class SisterOpenHelper extends SQLiteOpenHelper{
private static final String DB_NAME = "sister.db"; //數據庫名
private static final int DB_VERSION = 1; //數據庫版本號
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) { }
}
再接著，我們需要編寫一個數據庫的操作類，就是做增刪改查，分頁查詢等操作的類，
這裡我們把這個類寫成單例的：SisterDBHelper.java，裡面的編寫的方法有這些：
![\](https://android.yunyiwangluo.com/Android/UploadFiles_5356/201702/2017022217301172.png "\")
具體代碼：
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());
}
/** 單例 */
public static SisterDBHelper getInstance() {
if(dbHelper == null) {
synchronized (SisterDBHelper.class) {
if(dbHelper == null) {
dbHelper = new SisterDBHelper();
}
}
}
return dbHelper;
}
/** 插入一個妹子 */
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(使用事務) */
public void insertSisters(ArrayList 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);
}
}
}
/** 刪除妹子(根據_id) */
public void deleteSister(String _id) {
db = getWritableDB();
db.delete(TableDefine.TABLE_FULI,"_id =?",new String[]{_id});
closeIO(null);
}
/** 刪除所有妹子 */
public void deleteAllSisters() {
db = getWritableDB();
db.delete(TableDefine.TABLE_FULI,null,null);
closeIO(null);
}
/** 更新妹子信息(根據_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);
}
/** 查詢當前表中有多少個妹子 */
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;
}
/** 分頁查詢妹子，參數為當前頁和每一個的數量，頁數從0開始算 */
public List getSistersLimit(int curPage,int limit) {
db = getReadableDB();
List sisters = new ArrayList<>();
String startPos = String.valueOf(curPage * limit); //數據開始位置
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;
}
/** 查詢所有妹子 */
public List getAllSisters() {
db = getReadableDB();
List 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;
}
/** 獲得可寫數據庫的方法 */
private SQLiteDatabase getWritableDB() {
return sqlHelper.getWritableDatabase();
}
/** 獲得可讀數據庫的方法 */
private SQLiteDatabase getReadableDB() {
return sqlHelper.getReadableDatabase();
}
/** 關閉cursor和數據庫的方法 */
private void closeIO(Cursor cursor) {
if(cursor != null) {
cursor.close();
}
if(db != null) {
db.close();
}
}
}
嗯，還是蠻簡單的，都是一些SQLite的方法調用而已，接著我們對布局做一下更改，
把activity_main.xml改成下面的代碼，就是換成上一個和下一個這樣：
最後就是對MainActivity.java的一些邏輯更改了，核心的要點如下：
1.curPos和page的控制以及處理邏輯
2.根據網絡是否可用加載網絡還是數據庫數據
3.加載網絡數據時存儲到數據庫需要避免重復插入 等等。
代碼實現：
public class MainActivity extends AppCompatActivity implements View.OnClickListener {
private Button previousBtn;
private Button nextBtn;
private ImageView showImg;
private ArrayList data;
private int curPos = 0; //當前顯示的是哪一張
private int page = 1; //當前頁數
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> {
public SisterTask() {
}
@Override
protected ArrayList doInBackground(Void... params) {
ArrayList result = new ArrayList<>();
if (page < (curPos + 1) / 10 + 1) {
++page;
}
//判斷是否有網絡
if (NetworkUtils.isAvailable(getApplicationContext())) {
result = sisterApi.fetchSister(10, page);
//查詢數據庫裡有多少個妹子，避免重復插入
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 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);
}
}
}
操作步驟：
把項目跑起來後，一直按下一頁下一頁緩存一堆圖片，接著斷開網絡，進入DrySister，Duang~，神奇的發現，有妹子出現了，按下一頁或者上一頁也可以切換圖片，媽媽再也不用擔心我在沒網的時候不可以看DrySister了！
運行截圖：
![\](https://android.yunyiwangluo.com/Android/UploadFiles_5356/201702/2017022217301103.gif "\")
好的，本節在上節的基礎上行添加了SQlite保存後台數據，當無網的時候也可以查看妹子圖片，代碼的大的改動如上述，還有一些小改，具體看代碼。
最後把db分支的代碼合並到develop分支上，然後刪除db分支，把更新後的develop分支推送到Github！
代碼下載：https://github.com/coder-pig/DrySister/tree/develop
歡迎follow，star，覺得有什麼想加進來的可以提下issues！
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