我们在开发应用商店应用时，需要app具有缓存的功能，这样在离线模式下，仍能工作。我们选择的project为Hub。
这里采取的策略是：在HubPage.xaml.cs（之所以不选择App.xaml.cs，是为了能让用户一边操作界面一边进行下载）中，利用await异步编程，避免阻塞UI，先读取存有图片路径的JSON，然后解析该JSON得到每一张图片的URI，再根据URI下载图片，对于文字资源，直接下载JSON。这里要特别注意文件操作——文件权限，同时更要注意文件流的选取——如果选择不当会导致在下载图片时偶然性僵死。
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;
//“中心页”项模板在 http://go.microsoft.com/fwlink/?LinkID=321224 上有介绍
namespace demo02
{
public sealed partial class HubPage : Page
{
//一个容器，里面存有每个图片的url对象
//将JSON中存的图片的uri读取到PicArray，然后通过PicArray下载图片
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) //如果网络是连接的，进行缓存下载
{
if (OfflineFirstFlag.isFirstEnter) //由于之后会多次进入HubPage页面，我们只应当在第一次进入页面时进行下载
{
OfflineFirstFlag.isFirstEnter = false;
//获得图片资源，先下载存有uri的JSON，再解析JSON，再通过解析出的uri下载图片
//获取存有用于离线模式下图片uri的JSON
await HttpGetOfflinePICSJSON();
//获取存有老师和地域图片的url的JSON
await HttpGetOfflineTeacherRegionJSON();
//获得第一部分图片
await HttpGetOfflingPicByUrl();
//获得第二部分图片
await HttpGetOfflingPicByUrl02();
//获得第三部分图片
await HttpGetOfflingPicByUrl03();
//获得第四部分图片
await HttpGetOfflingPicByUrl04();
//获得文字资源
//获得离线模式数据展示的来源JSON
await HttpGetOfflineJSON();
}
}
}
//向服务器请求最新的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;
// 获取指定的文件中的文本内容
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;
// 获取指定的文件中的文本内容
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;
// 获取指定的文件中的文本内容
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);
//接着下载老师和地域的图片
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;
// 获取指定的文件中的文本内容
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)
{
//开始下载图片
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
{
//该类的作用是将服务器端的文件uri通过http下载到本地指定目录，并命名
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;
}
//不带返回值的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\AppX
break;
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);
//选择恰当的流，避免下载图片过程中僵死
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;
}
// 进度
totalBytesRead += buffer.Length;
System.Diagnostics.Debug.WriteLine("Bytes read: {0}", totalBytesRead);
// 写文件.
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; }
}
}