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:
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(ArrayListsisters) { 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 ArrayListdata; 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:
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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