一、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~
二、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：
- curPos和page的控制以及处理逻辑
- 根据网络是否可用加载网络还是数据库数据
- 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);
}
}
}
三、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：
四、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！
五、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！