引言

學習《android第一行程式碼》根據書本開發的天氣預報app，主要用於熟練操作android開發（android studio3.0平臺）。

今天主要分享一下從伺服器上獲取天氣資訊，通過ListView繫結資料的操作（可以採用RecycleView），然後進行頁面點選跳轉。

一、 伺服器返回資料預覽

通過本書作者提供的訪問地址，guolin.tech/api/china，直接開啟可以訪問到全國各地的天氣資訊，guolin.tech/api/china/16/116

（如點選無法開啟，請直接複製連結在瀏覽器中訪問）

[
 {"id":1,"name":"北京"},{"id":2,"name":"上海"},{"id":3,"name":"天津"},{"id":4,"name":"重慶"},
 {"id":5,"name":"香港"},{"id":6,"name":"澳門"},{"id":7,"name":"臺灣"},{"id":8,"name":"黑龍江"},
 {"id":9,"name":"吉林"},{"id":10,"name":"遼寧"},{"id":11,"name":"內蒙古"},{"id":12,"name":"河北"},
 {"id":13,"name":"河南"},{"id":14,"name":"山西"},{"id":15,"name":"山東"},{"id":16,"name":"江蘇"},
 {"id":17,"name":"浙江"},{"id":18,"name":"福建"},{"id":19,"name":"江西"},{"id":20,"name":"安徽"},
 {"id":21,"name":"湖北"},{"id":22,"name":"湖南"},{"id":23,"name":"廣東"},{"id":24,"name":"廣西"},
 {"id":25,"name":"海南"},{"id":26,"name":"貴州"},{"id":27,"name":"雲南"},{"id":28,"name":"四川"},
 {"id":29,"name":"西藏"},{"id":30,"name":"陝西"},{"id":31,"name":"寧夏"},{"id":32,"name":"甘肅"},
 {"id":33,"name":"青海"},{"id":34,"name":"新疆"}
]

如上面看到的可以獲取到各省的資訊，通過id可以進一步的獲取市縣的資訊。

二、建立本地資料儲存

根據伺服器中獲取的資料屬性，建立Province、City、County三個資料表分別儲存省、市、縣的資訊。

建立資料表採用Litepal，這裡需要匯入外部庫，需要在build.gradle中新增

implementation 'org.litepal.android:core:1.4.1'
（注implemention為android3.0以上版本才有的，與compile並不完全一樣，這裡不多做解釋，2.0版本採用compile不影響
同時在載入外部庫時可能出現無法引用的問題，請清理專案後重新build）
 

後面1.4.1是版本號，可以查詢官網獲取最新版本

下面附上三個資料表類，由於是採用Litepal需要繼承DataSupport

public class Province extends DataSupport {

    private int id;
    private String provinceName;
    private int provinceCode;

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    
 
public String getProvinceName() {
        return provinceName;
    }

    public void setProvinceName(String provinceName) {
        this.provinceName = provinceName;
    }

    public int getProvinceCode() {
        return provinceCode;
    }

    public void setProvinceCode(int provinceCode) {
        this.provinceCode = provinceCode;
    }
}

public class City extends DataSupport {
    private int id;
    private String cityName;
    private int cityCode;
    private int provinceId;

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getCityName() {
        return cityName;
    }

    public void setCityName(String cityName) {
        this.cityName = cityName;
    }

    public int getCityCode() {
        return cityCode;
    }

    public void setCityCode(int cityCode) {
        this.cityCode = cityCode;
    }

    public int getProvinceId() {
        return provinceId;
    }

    public void setProvinceId(int provinceId) {
        this.provinceId = provinceId;
    }
}

public class County extends DataSupport {
    private int id;
    private String countyName;
    private String weatherId;
    private int cityId;


    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getCountyName() {
        return countyName;
    }

    public void setCountyName(String countyName) {
        this.countyName = countyName;
    }

    public String getWeatherId() {
        return weatherId;
    }

    public void setWeatherId(String weatherId) {
        this.weatherId = weatherId;
    }

    public int getCityId() {
        return cityId;
    }

    public void setCityId(int cityId) {
        this.cityId = cityId;
    }
}

這三個類用來生成本地資料庫

接下來新建一個litepal.xml配置檔案，在main目錄下新建assets配置資料夾，新增litepal.xml

<litepal>
    <dbname value ="cool_weather"/>
    <version value = "1"/>
    <list>
        <mapping class="com.coolweather2.db.Province"/>
        <mapping class="com.coolweather2.db.County"/>
        <mapping class="com.coolweather2.db.City"/>
    </list>
</litepal>

此檔案通過Litepal建立了cool_weather資料庫同時添加了三個資料表

最後在androidmanifest.xml中新增LitepalApplication，如下

這樣Litepal可以全域性呼叫Context，注意如果不加，預設啟動時會初始化Application類

三、編寫工具包類

3.1HttpUtil

public class HttpUtil {

    public static void sendOkHttpRequest(String address,okhttp3.Callback callback) {
        OkHttpClient client  = new OkHttpClient();
        //request屬於不能繼承的類初始化Builder靜態類呼叫url方法，最後呼叫Requset的build方法
        Request request = new Request.Builder().url(address).build();
        client.newCall(request).enqueue(callback);
    }
}

主要用來想伺服器傳送請求，建立request並設定好其地址，通過client發起請求並設定callback回撥請求

3.2Utility

public class Utillty {
    /*解析和處理伺服器返回的省級資料*/
    public static boolean handleProvinceResponse(String response) {
        if(!TextUtils.isEmpty(response)) {
            try
            {
                JSONArray allProvinces = new JSONArray(response);
                for(int i = 0;i < allProvinces.length(); i++) {
                    JSONObject privinceObject = allProvinces.getJSONObject(i);
                    Province province = new Province();
                    province.setProvinceName(privinceObject.getString("name"));
                    province.setProvinceCode(privinceObject.getInt("id"));
                    province.save();
                }
                return true;
            }
            catch (JSONException ex) {
                ex.printStackTrace();
            }


        }
        return false;
    }


    /**
     * 解析和處理伺服器返回的市級資料
     * */
    public static boolean handleCityResponse(String response,int provinceId) {
        if(!TextUtils.isEmpty(response)) {
            try
            {
                JSONArray allCities = new JSONArray(response);
                for(int i = 0;i < allCities.length(); i++) {
                    JSONObject cityObject = allCities.getJSONObject(i);
                    City city = new City();
                    city.setCityName(cityObject.getString("name"));
                    city.setCityCode(cityObject.getInt("id"));
                    city.setProvinceId(provinceId);
                    city.save();
                }
                return true;
            }
            catch (JSONException ex) {
                ex.printStackTrace();
            }


        }
        return false;
    }

    /**
     * 解析和處理服器返回的縣級資料
     * */
    public static boolean handleCountyResponse(String response,int cityId) {
        if(!TextUtils.isEmpty(response)) {
            try
            {
                JSONArray allCountries = new JSONArray(response);
                for(int i = 0;i < allCountries.length(); i++) {
                    JSONObject countyObject = allCountries.getJSONObject(i);
                    County county = new County();
                    county.setCountyName(countyObject.getString("name"));
                    county.setWeatherId(countyObject.getString("weather_id"));
                    county.setCityId(cityId);
                    county.save();
                }
                return true;
            }
            catch (JSONException ex) {
                ex.printStackTrace();
            }


        }
        return false;
    }

主要處理從伺服器返回的資料，根據最開始的資料預覽可以看到，伺服器返回的資料是以Json格式輸出的

那麼這個工具類就是對json資料的分析處理，通過JSONArray陣列將json資料儲存在本地資料庫

有這裡的json資料比較簡單，直接進行解析，不採用GSON

四、建立碎片佈局

碎片有利於程式碼的複用，可以嘗試將自己的很多功能都通過碎片進行封裝

建立碎片會生成兩個檔案，一個是碎片的佈局檔案choose_area.xml，一個是ChooseAreaFragment.class

4.1佈局檔案

<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:background="#fff">


    <RelativeLayout
        android:layout_width = "match_parent"
        android:layout_height = "?attr/actionBarSize"
        android:background="?attr/colorPrimary">
        <TextView
            android:id="@+id/title_text"
            android:layout_centerInParent="true"
            android:textColor="#fff"
            android:textSize="20sp"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content" />
        <Button
            android:id="@+id/back_button"
            android:layout_width="25dp"
            android:layout_marginLeft="10dp"
            android:layout_alignParentLeft="true"
            android:layout_centerVertical="true"
            android:layout_height="25dp"
            android:background="@drawable/ic_launcher_background"/>
    </RelativeLayout>


    <ListView
        android:id="@+id/list_view"
        android:layout_width="match_parent"
        android:layout_height="match_parent"></ListView>

</LinearLayout>

簡單的兩個佈局，整體用線性佈局垂直對齊方式，頭部標題欄採用RecycleLayout佈局，設定一個回撥按鈕和一個標題文字框

底部一個listview用來顯示天氣列表

4.2ChooseAreaFragment.class

public class ChooseAreaFragment extends Fragment {

    public static final int LEVEL_PROVINCE = 0;
    public static final int LEVEL_CITY = 1;
    public static final int LEVEL_COUNTY = 2;

    private ProgressDialog progressDialog;
    private TextView titleText;
    private Button backButton;
    private ListView listView;
    private ArrayAdapter<String> adapter;
    private List<String> dataList = new ArrayList<>();

    private List<Province> provinceList;
    private List<City> cityList;
    private List<County> countyList;

    private Province selectedProvince;
    private City selectedCity;
    private int currentLevel;



    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.choose_area,container,false);
        titleText = (TextView)view.findViewById(R.id.title_text);
        backButton = (Button)view.findViewById(R.id.back_button);
        listView = (ListView)view.findViewById(R.id.list_view);

        adapter = new ArrayAdapter<String>(getContext(), R.layout.support_simple_spinner_dropdown_item,dataList);
        listView.setAdapter(adapter);
        return view;
    }

    @Override
    public void onActivityCreated(@Nullable Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);


        queryProvinces();

        listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
                if(currentLevel == LEVEL_PROVINCE) {
                    selectedProvince = provinceList.get(position);
                    queryCities();
                }
                else if (currentLevel == LEVEL_CITY) {
                    selectedCity = cityList.get(position);
                    queryCountries();
                }
            }
        });

        backButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                if (currentLevel == LEVEL_COUNTY) {
                    queryCities();
                }
                else if (currentLevel == LEVEL_CITY) {
                    queryProvinces();
                }
            }
        });


    }


    /**
     * 查詢所有省，查資料庫，再查伺服器
     */
    private void queryProvinces() {
        titleText.setText("中國");
        backButton.setVisibility(View.GONE);
        provinceList = DataSupport.findAll(Province.class);
        if(provinceList.size()>0) {
            dataList.clear();
            for (Province province :
                    provinceList) {
                dataList.add(province.getProvinceName());
            }
            adapter.notifyDataSetChanged();
            listView.setSelection(0);
            currentLevel = LEVEL_PROVINCE;
        }
        else {
            //伺服器查詢
            String address = "http://guolin.tech/api/china";
            queryFromServer(address,"province");
        }
    }

    /**
     * 查詢市
     */

    private void queryCities() {
        titleText.setText(selectedProvince.getProvinceName());
        backButton.setVisibility(View.VISIBLE);
        cityList = DataSupport.where("provinceid = ?",String.valueOf(selectedProvince.getId()))
                .find(City.class);
        if (cityList.size()>0) {
            dataList.clear();
            for (City city :
                    cityList) {
                dataList.add(city.getCityName());
            }
            adapter.notifyDataSetChanged();
            listView.setSelection(0);
            currentLevel = LEVEL_CITY;
        }
        else {
            //查詢伺服器
            int provinceCode = selectedProvince.getProvinceCode();
            String address = "http://guolin.tech/api/china/" + provinceCode;
            queryFromServer(address,"city");
        }
    }

    /**
     * 查詢縣
     */

    private void queryCountries(){
        titleText.setText(selectedCity.getCityName());
        backButton.setVisibility(View.VISIBLE);
        countyList = DataSupport.where("cityid = ?",String.valueOf(selectedCity.getId()))
                .find(County.class);
        if (countyList.size()>0) {
            dataList.clear();
            for (County county :
                    countyList) {
                dataList.add(county.getCountyName());
            }
            adapter.notifyDataSetChanged();
            listView.setSelection(0);
            currentLevel = LEVEL_COUNTY;

        }
        else {
            //訪問伺服器
            int provinceCode = selectedProvince.getProvinceCode();
            int cityCode = selectedCity.getCityCode();
            String address = "http://guolin.tech/api/china/" + provinceCode + "/" + cityCode;
            Toast.makeText(getContext(),provinceCode +"/" +  cityCode,Toast.LENGTH_LONG).show();
            queryFromServer(address,"county ");
        }
    }


    /**
     * 從伺服器查詢
     */
    private void queryFromServer(String address,final String type) {
        showProgressDialog();
        Toast.makeText(getContext(),type,Toast.LENGTH_SHORT).show();
        HttpUtil.sendOkHttpRequest(address, new Callback() {
            @Override
            public void onFailure(Call call, IOException e) {
                getActivity().runOnUiThread(new Runnable() {
                    @Override
                    public void run() {
                        closeProgressDialog();
                        Toast.makeText(getContext(),"載入失敗!",Toast.LENGTH_SHORT).show();
                    }
                });
            }

            @Override
            public void onResponse(Call call, Response response) throws IOException {
                String responText = response.body().string();
                boolean result = false;
                if("province".equals(type)) {
                    result = Utillty.handleProvinceResponse(responText);
                }
                else if ("city".equals(type)) {
                    result = Utillty.handleCityResponse(responText,selectedProvince.getId());
                }
                else if ("county".equals(type)){
                    //Toast.makeText(getContext(),"aaaaa",Toast.LENGTH_LONG).show();
                    result = Utillty.handleCountyResponse(responText,selectedCity.getId());
                }
                //Toast.makeText(getContext(),"" + result,Toast.LENGTH_SHORT).show();
                if (result) {
                    getActivity().runOnUiThread(new Runnable() {
                        @Override
                        public void run() {
                            closeProgressDialog();
                            if("province".equals(type)) {
                                queryProvinces();
                            }
                            else if ("city".equals(type)) {
                                queryCities();
                            }
                            else if ("county".equals(type)){
                                queryCountries();
                            }
                        }
                    });
                }
            }
        });
    }

    /**
     * 顯示進度框
     */
    private void showProgressDialog() {
        if(progressDialog == null) {
            progressDialog = new ProgressDialog(getActivity());
            progressDialog.setMessage("正在載入");
            progressDialog.setCanceledOnTouchOutside(false);
        }
        progressDialog.show();
    }


    /**
     * 關閉進度對話方塊
     */
    private void closeProgressDialog() {
        if (progressDialog != null) {
            progressDialog.dismiss();
        }
    }

這裡我把不需要用到的方法刪除，只留下onCreateView和onActivityCreated這兩個方法

一個表示建立佈局，主要用來載入佈局同時對部分資料進行初始化

onActivityCreated顯然是在佈局載入完之後才觸發的，主要的功能都在這裡面實現

主要實現的是listview的跳轉功能，判斷當前是那一級別的資料從而點選時獲取下一級別的資料，

如當前點選“江蘇”，首先返回按鈕顯示，標題改為“江蘇”，然後優先查詢資料庫資訊，當沒有找到時再向伺服器傳送請求

五、主活動中載入碎片

修改main佈局中的檔案

通過name在初始化時執行碎片

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".activity.MainActivity">

    <fragment
        android:id="@+id/choose_area_fragment"
        android:name="com.coolweather2.fragment.ChooseAreaFragment"

        android:layout_width="match_parent"
        android:layout_height="match_parent">

    </fragment>

</FrameLayout>

注意由於碎片中設定過標題，需要在styles.xml中修改預設標題

最後需要設定網路訪問許可權（Androidmanifest.xml）