来源:网易云课堂GeekBand第七次作业

作业要求:
做一个天气应用

1. 接口参考： http://apistore.baidu.com/apiworks/servicedetail/880.html，只是参考API，可自行查找使用其他API接口
2. 考察内容：获取数据，解析JSON
3. 数据缓存在数据库中，使用ContentProvider来处理
4. 如果不强制刷新，则使用缓存数据每隔一定时间再刷新一次

前期准备

1.选择合适的API!选择合适的API!选择合适的API!(重要的话说三遍,中途变更API严重影响效率和心情).
2.gson.如何添加依赖库 http://www.cnblogs.com/happyhacking/p/5257002.html

目录结构

UI

注意:在布局的过程中weightSum和layout_weight要慎用,尤其是在内容长度可变的情况下,使用结果往往不符合预期.

主要逻辑

主要逻辑集中在查询按钮的点击事件上

(注意:cursor.moveToFirst(),Long.valueOf()和Long.getLong()的用法.)

 mQueryButton.setOnClickListener(new View.OnClickListener() {@Overridepublic void onClick(View v) {//判断用户是否输入了城市名称if (!TextUtils.isEmpty(mCityName.getText())) {//首先查询本地数据库Uri uri = Uri.parse("content://com.example.janiszhang.weatherdemo.provider/weatherdata");Cursor cursor = getContentResolver().query(uri, null, "cityname = ?", new String[]{mCityName.getText() + ""}, null);if (cursor.moveToFirst()) {// 查询成功    //这里不可以使用cursor!= null来判断!!!!Log.i("zhangbz", cursor.getString(cursor.getColumnIndex("savetime")));if ((System.currentTimeMillis() - Long.valueOf(cursor.getString(cursor.getColumnIndex("savetime")))) < (1000*60)) {//这里不可以使用Long.getLong(),因为它返回的是系统属性的值,其参数是被请求的系统属性的名称//如果数据库中的数据没有过期,就从数据库中查询updateUIfromDatabase(cursor);} else {//如果数据库中的数据过期了,则通过网络查询并update到数据库shouldUpdate = true;try {httpArg = "city=" + URLEncoder.encode(mCityName.getText().toString(), "UTF-8");//中文需要编码} catch (UnsupportedEncodingException e) {e.printStackTrace();}new MyAsyncTask().execute(httpArg);//使用asynctask}} else {//网络查询并insert到数据库shouldUpdate = false;//需要inserttry {httpArg = "city=" + URLEncoder.encode(mCityName.getText().toString(), "UTF-8");//中文需要编码} catch (UnsupportedEncodingException e) {e.printStackTrace();}new MyAsyncTask().execute(httpArg);}SharedPreferences sp = getSharedPreferences("last", Context.MODE_PRIVATE);SharedPreferences.Editor editor = sp.edit();editor.putString("cityname", mCityName.getText().toString());editor.apply();//开启自动更新Intent intent = new Intent(MainActivity.this, AutoUpdateService.class);startService(intent);}}});

重点记录

使用Gson解析数据

            Gson gson = new Gson();WeatherDataStatus weatherDataStatus = gson.fromJson(s, WeatherDataStatus.class);

这里注意两个问题:
1.使用gson解析json数据时,不需要为整个json数据创建实体类,只需要为需要解析的数据定义变量和提供getter/setter方法.
2.注意区分什么是json数组:

        //json数组:中括号[{"这是json数组": "这是json数组"}, {"这是json数组": "这是json数组"}, {"这是json数组": "这是json数组"}]//注意和这种情况区分开{"这不是json数组": [{"这才是json数组": "这才是json数组"}, {"这才是json数组": "这才是json数组"}, {"这才是json数组": "这才是json数组"}]}

自动更新的实现

service需要由Activity启动,之后由service和receiver配合相互唤醒.

AutoUpdateService.class

public class AutoUpdateService extends Service{private String mCityname;@Nullable@Overridepublic IBinder onBind(Intent intent) {return null;}@Overridepublic int onStartCommand(Intent intent, int flags, int startId) {//在子线程中发起网络请求,将请求结果保存到数据库中new Thread(new Runnable() {@Overridepublic void run() {updateWeather();}}).start();//使用AlarmManager实现定时任务AlarmManager manager = (AlarmManager) getSystemService(ALARM_SERVICE);int anHour = 8 * 60 *60 * 1000;//8小时long triggerAtTime = SystemClock.elapsedRealtime() + anHour;//service -> receiverIntent i = new Intent(this, AutoUpdateReceiver.class);PendingIntent pi = PendingIntent.getBroadcast(this, 0, i, 0);manager.set(AlarmManager.ELAPSED_REALTIME_WAKEUP, triggerAtTime, pi);return super.onStartCommand(intent, flags, startId);}//...}

AutoUpdateReceiver.class

public class AutoUpdateReceiver extends BroadcastReceiver{@Overridepublic void onReceive(Context context, Intent intent) {//receiver->serviceIntent i = new Intent(context, AutoUpdateService.class);context.startService(i);}
}

contentprovider的练习

虽然用在这里很牵强,但是目的是练习嘛.
很久没有使用contentprovider,以下为基本使用方法.

public class MyProvider extends ContentProvider{public static final int WEATHERDATA_DIR = 0;public static final String AUTHORITY = "com.example.janiszhang.weatherdemo.provider";private static UriMatcher sUriMatcher;private MyDBHelper mMyDBHelper;static {sUriMatcher = new UriMatcher(UriMatcher.NO_MATCH);sUriMatcher.addURI(AUTHORITY, "weatherdata", WEATHERDATA_DIR);}@Overridepublic boolean onCreate() {mMyDBHelper = new MyDBHelper(getContext(),  "weatherDataDB.db", null, 1);return true;}@Nullable@Overridepublic Cursor query(Uri uri, String[] projection, String selection, String[] selectionArgs, String sortOrder) {SQLiteDatabase db = mMyDBHelper.getReadableDatabase();Cursor cursor = null;switch (sUriMatcher.match(uri)) {case WEATHERDATA_DIR:cursor = db.query("weatherdata", projection, selection, selectionArgs, null, null, sortOrder);break;}return cursor;}@Nullable@Overridepublic String getType(Uri uri) {switch (sUriMatcher.match(uri)) {case WEATHERDATA_DIR:return "vnd.android.cursor.dir/vnd.com.example.janiszhang.weatherdemo.provider.weatherdata";}return null;}@Nullable@Overridepublic Uri insert(Uri uri, ContentValues values) {SQLiteDatabase db = mMyDBHelper.getReadableDatabase();Uri uriReturn = null;switch (sUriMatcher.match(uri)) {case WEATHERDATA_DIR:long newId = db.insert("weatherdata", null, values);uriReturn = Uri.parse("content://" + AUTHORITY + "/weatherdata/" + newId);break;}return uriReturn;}@Overridepublic int delete(Uri uri, String selection, String[] selectionArgs) {return 0;}@Overridepublic int update(Uri uri, ContentValues values, String selection, String[] selectionArgs) {SQLiteDatabase db = mMyDBHelper.getWritableDatabase();int updateRows = 0;switch (sUriMatcher.match(uri)) {case WEATHERDATA_DIR:updateRows = db.update("weatherdata", values, selection, selectionArgs);break;}return updateRows;}
}

github地址:https://github.com/zhangbz/WeatherDemo

总结:写这个demo,把四大组件都用到了,把基本用法复习了一遍,温故知新.