Win8.1應用開發之離線緩衝

標籤：win8   離線緩衝   

我們在開發市集應用時，需要app具有緩衝的功能，這樣在離線模式下，仍能工作。我們選擇的project為Hub。

這裡採取的策略是：在HubPage.xaml.cs（之所以不選擇App.xaml.cs，是為了能讓使用者一邊操作介面一邊進行下載）中，利用await非同步編程，避免阻塞UI，先讀取存有圖片路徑的JSON，然後解析該JSON得到每一張圖片的URI，再根據URI下載圖片，對於文字資源，直接下載JSON。這裡要特別注意檔案操作——檔案許可權，同時更要注意檔案流的選取——如果選擇不當會導致在下載圖片時偶然性僵死。

在HubPage.xaml.cs中：

using Bing.Maps;using demo02.Common;using demo02.Data;using demo02.DataModel;using demo02.DataStructure;using demo02.Entity;using demo02.Helper;using Newtonsoft.Json;using System;using System.Collections.Generic;using System.Collections.ObjectModel;using System.IO;using System.Linq;using System.Net.Http;using System.Runtime.InteropServices.WindowsRuntime;using System.Threading.Tasks;using WhereWeGo.Helper;using Windows.ApplicationModel.Search;using Windows.Foundation;using Windows.Foundation.Collections;using Windows.Storage;using Windows.UI;using Windows.UI.Popups;using Windows.UI.Xaml;using Windows.UI.Xaml.Controls;using Windows.UI.Xaml.Controls.Primitives;using Windows.UI.Xaml.Data;using Windows.UI.Xaml.Input;using Windows.UI.Xaml.Media;using Windows.UI.Xaml.Media.Animation;using Windows.UI.Xaml.Navigation;//“中心頁”項目範本在 http://go.microsoft.com/fwlink/?LinkID=321224 上有介紹namespace demo02{    public sealed partial class HubPage : Page    {        //一個容器，裡面存有每個圖片的url對象//將JSON中存的圖片的uri讀取到PicArray，然後通過PicArray下載圖片        private static OfflinePicArray PicArray { get; set; }         private NavigationHelper navigationHelper;        private ObservableDictionary defaultViewModel = new ObservableDictionary();        public HubPage()        {            this.InitializeComponent();            this.navigationHelper = new NavigationHelper(this);            this.navigationHelper.LoadState += navigationHelper_LoadState;        }         private async void navigationHelper_LoadState(object sender, LoadStateEventArgs e)        {            if (ConnectState.isConnected) //如果網路是串連的，進行緩衝下載            {                if (OfflineFirstFlag.isFirstEnter) //由於之後會多次進入HubPage頁面，我們只應當在第一次進入頁面時進行下載                {                    OfflineFirstFlag.isFirstEnter = false;//獲得圖片資源，先下載存有uri的JSON，再解析JSON，再通過解析出的uri下載圖片                    //擷取存有用於離線模式片uri的JSON                    await HttpGetOfflinePICSJSON();                    //擷取存有老師和地區圖片的url的JSON                    await HttpGetOfflineTeacherRegionJSON();                    //獲得第一部分圖片                    await HttpGetOfflingPicByUrl();//獲得第二部分圖片                    await HttpGetOfflingPicByUrl02();//獲得第三部分圖片                    await HttpGetOfflingPicByUrl03();//獲得第四部分圖片                    await HttpGetOfflingPicByUrl04();//獲得文字資源                    //獲得離線模式資料展示的來源JSON                    await HttpGetOfflineJSON();                }            }        }        //向伺服器請求最新的PICS JSON        private async static Task HttpGetOfflinePICSJSON()        {            XDownload xmen = new XDownload(ServiceUrl.URL_OFFLINE_PICSJSON, XDownload.App, OfflineSubFolder.Name, ServiceUrl.PICSJSON_LOCALNAME);            await xmen.GetDataAsync();        }        private async static Task HttpGetOfflingPicByUrl()        {            try {                StorageFolder storageFolder = Windows.ApplicationModel.Package.Current.InstalledLocation;                StorageFolder folder = await storageFolder.GetFolderAsync(OfflineSubFolder.Name);                StorageFile storageFile = await folder.GetFileAsync(ServiceUrl.PICSJSON_LOCALNAME);                if (storageFile != null)                {                    XDownload bigOverhead = new XDownload();                    bigOverhead.Library = XDownload.App;                    bigOverhead.Myfolder = OfflineSubFolder.Name;                    // 擷取指定的檔案中的常值內容                    string textContent = await FileIO.ReadTextAsync(storageFile, Windows.Storage.Streams.UnicodeEncoding.Utf8);                    PicArray = JsonConvert.DeserializeObject<OfflinePicArray>(textContent);                    foreach (OfflinePicUri onePic in PicArray.Images)                    {                        foreach (string picName in onePic.ShowImages)                        {                            if (picName != null)                            {                                bigOverhead.Uri = ServiceUrl.BASEURL_OFFLINE + onePic.ImageFolder + picName;                                System.Diagnostics.Debug.WriteLine(bigOverhead.Uri + "kakakakakakkakakak");                                bigOverhead.Filename = picName;                                await bigOverhead.GetDataAsync();                            }                        }                    }                 } catch(Exception ex) {                            }                  }        private async static Task HttpGetOfflingPicByUrl02()        {            try            {                StorageFolder storageFolder = Windows.ApplicationModel.Package.Current.InstalledLocation;                StorageFolder folder = await storageFolder.GetFolderAsync(OfflineSubFolder.Name);                StorageFile storageFile = await folder.GetFileAsync(ServiceUrl.PICSJSON_LOCALNAME);                if (storageFile != null)                {                    XDownload bigOverhead = new XDownload();                    bigOverhead.Library = XDownload.App;                    bigOverhead.Myfolder = OfflineSubFolder.Name;                    // 擷取指定的檔案中的常值內容                    string textContent = await FileIO.ReadTextAsync(storageFile, Windows.Storage.Streams.UnicodeEncoding.Utf8);                    PicArray = JsonConvert.DeserializeObject<OfflinePicArray>(textContent);                    foreach (OfflinePicUri onePic in PicArray.Images)                    {                        if (onePic.TileImagePath != null)                        {                            bigOverhead.Uri = ServiceUrl.BASEURL_OFFLINE + onePic.ImageFolder + onePic.TileImagePath;                            bigOverhead.Filename = onePic.TileImagePath;                            await bigOverhead.GetDataAsync();                        }                    }                }            }            catch (Exception ex) {                            }                }        private async static Task HttpGetOfflingPicByUrl03()        {            try {                StorageFolder storageFolder = Windows.ApplicationModel.Package.Current.InstalledLocation;                StorageFolder folder = await storageFolder.GetFolderAsync(OfflineSubFolder.Name);                StorageFile storageFile = await folder.GetFileAsync(ServiceUrl.PICSJSON_LOCALNAME);                if (storageFile != null)                {                    XDownload bigOverhead = new XDownload();                    bigOverhead.Library = XDownload.App;                    bigOverhead.Myfolder = OfflineSubFolder.Name;                    // 擷取指定的檔案中的常值內容                    string textContent = await FileIO.ReadTextAsync(storageFile, Windows.Storage.Streams.UnicodeEncoding.Utf8);                    PicArray = JsonConvert.DeserializeObject<OfflinePicArray>(textContent);                    foreach (OfflinePicUri onePic in PicArray.Images)                    {                        if (onePic.Badge != null)                        {                            bigOverhead.Uri = ServiceUrl.BASEURL_OFFLINE + onePic.ImageFolder + onePic.Badge;                            bigOverhead.Filename = onePic.Badge;                            await bigOverhead.GetDataAsync();                        }                    }                }            } catch(Exception ex) {                            }                 }        private async Task HttpGetOfflingPicByUrl04()        {            try {                StorageFolder storageFolder = Windows.ApplicationModel.Package.Current.InstalledLocation;                StorageFolder folder = await storageFolder.GetFolderAsync(OfflineSubFolder.Name);                //接著下載老師和地區的圖片                StorageFile storageFile01 = await folder.GetFileAsync(ServiceUrl.T_R_JSON_LOCALNAME);                if (storageFile01 != null)                {                    XDownload bigOverhead = new XDownload();                    bigOverhead.Library = XDownload.App;                    bigOverhead.Myfolder = OfflineSubFolder.Name;                    // 擷取指定的檔案中的常值內容                    string textContent = await FileIO.ReadTextAsync(storageFile01, Windows.Storage.Streams.UnicodeEncoding.Utf8);                    TRPic tr = new TRPic();                    tr = JsonConvert.DeserializeObject<TRPic>(textContent);                    foreach (string onePic in tr.TeacherImages)                    {                        //開始下載圖片                               bigOverhead.Uri = ServiceUrl.BASEURL_OFFLINE + onePic;                        bigOverhead.Filename = TeaRegFilter.GetPicName(onePic);                        await bigOverhead.GetDataAsync();                    }                }            }catch (Exception ex) {                            }        }        private async static Task HttpGetOfflineJSON()        {            XDownload xmen = new XDownload(ServiceUrl.URL_OFFLINE_JSON, XDownload.App, OfflineSubFolder.Name, ServiceUrl.JSON_LOCALNAME);            await xmen.GetDataAsync();        }        private async static Task HttpGetOfflineTeacherRegionJSON()        {            XDownload xmen = new XDownload(ServiceUrl.URL_OFFLINE_TEACHER_REGION_JSON, XDownload.App, OfflineSubFolder.Name, ServiceUrl.T_R_JSON_LOCALNAME);            await xmen.GetDataAsync();        }    }}using System;using System.Collections.Generic;using System.IO;using System.Linq;using System.Net.Http;using System.Text;using System.Threading.Tasks;using Windows.Networking.BackgroundTransfer;using Windows.Storage;using Windows.Storage.Streams;namespace demo02.Helper{    //該類的作用是將伺服器端的檔案uri通過http下載到本地指定目錄，並命名    public class XDownload    {        public static string Documents = "Documents";        public static string Pictures = "Pictures";        public static string Music = "Music";        public static string Videos = "Videos";        public static string App = "App";         public XDownload()        {            this.Uri = "";            this.Library = "";            this.Myfolder = "";            this.Filename = "";        }        public XDownload(String uri, String library, String myfolder, String filename)        {            this.Uri = uri;            this.Library = library;            this.Myfolder = myfolder;            this.Filename = filename;        }        //不帶傳回值的Task        public async Task GetDataAsync()        {            StorageFolder folder = null;            try            {                switch (this.Library)                {                     case "Documents":                        folder = KnownFolders.DocumentsLibrary;                        break;                    case "Pictures":                        folder = KnownFolders.PicturesLibrary;                        break;                    case "Music":                        folder = KnownFolders.MusicLibrary;                        break;                    case "Videos":                        folder = KnownFolders.VideosLibrary;                        break;                    case "App":folder = Windows.ApplicationModel.Package.Current.InstalledLocation; //C:\Users\tom\Documents\GitHub\wherewegov1\wherewego\demo02\bin\Debug\AppXbreak;                    default:                        System.Diagnostics.Debug.WriteLine("ERROR: Make sure you are using the four special library: Documents, Music, Videos, Pictures");                        return;                }                if (this.Myfolder == "")                {                    System.Diagnostics.Debug.WriteLine("ERROR: Make sure you input a valid subfolder");                    return;                }                StorageFolder childFolder = await folder.CreateFolderAsync(this.Myfolder, CreationCollisionOption.OpenIfExists);                    if (this.Filename == "")                {                    System.Diagnostics.Debug.WriteLine("ERROR: Make sure you input a valid filename");                    return;                }                //Creates a new file in the current folder, and specifies what to do if                 //a file with the same name already exists in the current folder.                StorageFile outputFile = await childFolder.CreateFileAsync(this.Filename, CreationCollisionOption.ReplaceExisting);              //選擇恰當的流，避免下載圖片過程中僵死var fs = await outputFile.OpenAsync(FileAccessMode.ReadWrite);                HttpClientHandler handler = new HttpClientHandler();                handler.ClientCertificateOptions = ClientCertificateOption.Automatic;                HttpClient hc = new HttpClient(handler);                HttpResponseMessage response = await hc.GetAsync(this.Uri, HttpCompletionOption.ResponseHeadersRead);                Stream stream = await response.Content.ReadAsStreamAsync();                IInputStream inputStream = stream.AsInputStream();                ulong totalBytesRead = 0;                while (true)                {                    // Read from the web.                      IBuffer buffer = new Windows.Storage.Streams.Buffer(1024);                    buffer = await inputStream.ReadAsync(                        buffer,                        buffer.Capacity,                        InputStreamOptions.None);                    if (buffer.Length == 0)                    {                        // 完成                          break;                    }                    // 進度                      totalBytesRead += buffer.Length;                    System.Diagnostics.Debug.WriteLine("Bytes read: {0}", totalBytesRead);                    // 寫檔案.                      await fs.WriteAsync(buffer);                }                inputStream.Dispose();                fs.Dispose();              }            catch (Exception)            {                System.Diagnostics.Debug.WriteLine("ERROR: file download failed, tai can le");            }        }        public string Uri { get; set; }        public string Library { get; set; }        public string Myfolder { get; set; }        public string Filename { get; set; }     }}