以上按12個(gè)場景進(jìn)行代碼分析，下面從技術(shù)點(diǎn)的角度來分析代碼：
技術(shù)點(diǎn)1：這個(gè)應(yīng)用中，在表示層大量使用了一種自定義控件，繼承了Repeater類。先看看全文檢索寵物調(diào)用Simplepager的方式：
Part 1 頁面代碼，先引入標(biāo)簽，后使用標(biāo)簽。使用標(biāo)簽時(shí)，先設(shè)置屬性，后設(shè)置模板。這個(gè)標(biāo)簽可以設(shè)置頁面大小，當(dāng)沒有條目時(shí)，給出提示，分頁時(shí)用了一個(gè)onpageindexchanged事件。
<PetsControl:simplepager id="products" runat="server" pagesize="4" emptytext="No products found." onpageindexchanged="PageChanged">
<headertemplate>
<table cellpadding="0" cellspacing="0">
<tr class="gridHead">
<td>Product ID</td>
<td>Name</td>
<td>Description</td>
</tr>
</headertemplate>
<itemtemplate>
<tr class="gridItem">
<td><%
# DataBinder.Eval(Container.DataItem, "Id") %></td>
<td><a href='Items.aspx?productId=<%# DataBinder.Eval(Container.DataItem, "Id") %>'><%# DataBinder.Eval(Container.DataItem, "Name") %></a></td>
<td><%# DataBinder.Eval(Container.DataItem, "Description") %></td>
</tr>
</itemtemplate>
<footertemplate>
</tbody>
</table>
</footertemplate>
</PetsControl:simplepager>在
onpageindexchanged事件中，綁定數(shù)據(jù)源。
protected void PageChanged(object sender, DataGridPageChangedEventArgs e) {
products.CurrentPageIndex = e.NewPageIndex;
// Get the search terms from the query string
string searchKey = WebComponents.CleanString.InputText(Request["keywords"], 100);
if (searchKey != ""){
// Create a data cache key
string cacheKey = "search" + searchKey;
// Check if the objects are in the cache
if(Cache[cacheKey] != null){
products.DataSource = (IList)Cache[cacheKey];
}else{
// If that data is not in the cache then use the business logic tier to fetch the data
Product product = new Product();
IList productsBySearch = product.GetProductsBySearch(searchKey);
// Store the results in a cache
Cache.Add(cacheKey, productsBySearch, null, DateTime.Now.AddHours(12), Cache.NoSlidingExpiration , CacheItemPriority.High, null);
products.DataSource = productsBySearch;
}
// Databind the data to the controls
products.DataBind();
}
}
Part 2 看看SimplePager的源代碼。在源代碼中，SimplePager繼承了Repeater，主要增添了分頁功能，大部分是屬性的定義，增加了OnPageIndexChanged事件，重寫了OnLoad、Render和OnDataBinding方法。Onload獲取請求參數(shù)，激發(fā)分頁事件。Render描述了如何渲染這個(gè)控件，OnDataBinding告訴控件要綁定哪些數(shù)據(jù)。
public class SimplePager : Repeater {
//Static constants
protected const string HTML1 = "<table cellpadding=0 cellspacing=0><tr><td colspan=2>";
protected const string HTML2 = "</td></tr><tr class=gridNav><td>";
protected const string HTML3 = "</td><td align=right>";
protected const string HTML4 = "</td></tr></table>";
private static readonly Regex RX = new Regex(@"^&page=\d+", RegexOptions.Compiled);
private const string LINK_PREV = "<a href=?page={0}><img src=Images/buttonPrev.gif alt=Previous border=\"0\"></a>";
private const string LINK_MORE = "<a href=?page={0}><img src=Images/buttonMore.gif alt=More border=\"0\"></a>";
private const string KEY_PAGE = "page";
private const string COMMA = "?";
private const string AMP = "&";
protected string emptyText;
private IList dataSource;
private int pageSize = 10;
private int currentPageIndex;
private int itemCount;
override public object DataSource {
set {
//This try catch block is to avoid issues with the VS.NET designer
//The designer will try and bind a datasource which does not derive from ILIST
try{
dataSource = (IList)value;
ItemCount = dataSource.Count;
}catch{
dataSource = null;
ItemCount = 0;
}
}
}
public int PageSize {
get { return pageSize; }
set { pageSize = value; }
}
protected int PageCount {
get { return (ItemCount - 1) / pageSize; }
}
virtual protected int ItemCount {
get { return itemCount; }
set { itemCount = value; }
}
virtual public int CurrentPageIndex {
get { return currentPageIndex; }
set { currentPageIndex = value; }
}
public string EmptyText {
set { emptyText = value; }
}
public void SetPage(int index) {
OnPageIndexChanged(new DataGridPageChangedEventArgs(null, index));
}
override protected void OnLoad(EventArgs e) {
if (Visible) {
string page = Context.Request[KEY_PAGE];
int index = (page != null) ? int.Parse(page) : 0;
SetPage(index);
}
}
/**//// <summary>
/// Overriden method to control how the page is rendered
/// </summary>
/// <param name="writer"></param>
override protected void Render(HtmlTextWriter writer) {
//Check there is some data attached
if (ItemCount == 0) {
writer.Write(emptyText);
return;
}
//Mask the query
string query = Context.Request.Url.Query.Replace(COMMA, AMP);
query = RX.Replace(query, string.Empty);
// Write out the first part of the control, the table header
writer.Write(HTML1);
// Call the inherited method
base.Render(writer);
// Write out a table row closure
writer.Write(HTML2);
//Determin whether next and previous buttons are required
//Previous button?
if (currentPageIndex > 0)
writer.Write(string.Format(LINK_PREV, (currentPageIndex - 1) + query));
//Close the table data tag
writer.Write(HTML3);
//Next button?
if (currentPageIndex < PageCount)
writer.Write(string.Format(LINK_MORE, (currentPageIndex + 1) + query));
//Close the table
writer.Write(HTML4);
}
override protected void OnDataBinding(EventArgs e) {
//Work out which items we want to render to the page
int start = CurrentPageIndex * pageSize;
int size = Math.Min(pageSize, ItemCount - start);
IList page = new ArrayList();
//Add the relevant items from the datasource
for (int i = 0; i < size; i++)
page.Add(dataSource[start + i]);
//set the base objects datasource
base.DataSource = page;
base.OnDataBinding(e);
}
public event DataGridPageChangedEventHandler PageIndexChanged;
virtual protected void OnPageIndexChanged(DataGridPageChangedEventArgs e) {
if (PageIndexChanged != null)
PageIndexChanged(this, e);
}
}
Part 3 從上面的代碼你可以看出SimplePager有一個(gè)致命的缺點(diǎn)就是：如果一個(gè)頁面內(nèi)有兩個(gè)SimplePager控件怎么辦？如果他們還依賴于請求的URL附帶參數(shù)的話，兩個(gè)控件豈不是會沖突？ViewStatePager正是為解決這個(gè)問題的，在ViewStatePager中用ViewState記住各自控件的記錄數(shù)和當(dāng)前頁數(shù)。調(diào)用這個(gè)控件的地方是購物車頁面。
public class ViewStatePager : SimplePager {
private const string KEY_ITEM_COUNT = "ItemCount";
private const string KEY_CURRENT_PAGE_INDEX = "CurrentPageIndex";
private const string IMG_PREV = "Images/buttonPrev.gif";
private const string IMG_MORE = "Images/buttonMore.gif";
private const string ALT_PREV = "Previous";
private const string ALT_MORE = "More";
private ImageButton btnPrev;
private ImageButton btnMore;
override protected int ItemCount {
get { return (int)ViewState[KEY_ITEM_COUNT]; }
set { ViewState[KEY_ITEM_COUNT] = value; }
}
override public int CurrentPageIndex {
get { return (int)ViewState[KEY_CURRENT_PAGE_INDEX]; }
set { ViewState[KEY_CURRENT_PAGE_INDEX] = value; }
}
override protected void OnLoad(EventArgs e) {
if (!Page.IsPostBack && Visible) {
CurrentPageIndex = 0;
SetPage(0);
}
}
private void PreviousClicked(object sender, ImageClickEventArgs e) {
OnPageIndexChanged(new DataGridPageChangedEventArgs(sender, CurrentPageIndex - 1));
}
private void MoreClicked(object sender, ImageClickEventArgs e) {
OnPageIndexChanged(new DataGridPageChangedEventArgs(sender, CurrentPageIndex + 1));
}
override protected void CreateControlHierarchy(bool useDataSource) {
base.CreateControlHierarchy(useDataSource);
btnPrev = new ImageButton();
btnPrev.ImageUrl = IMG_PREV;
btnPrev.AlternateText = ALT_PREV;
btnPrev.Click += new ImageClickEventHandler(PreviousClicked);
Controls.Add(btnPrev);
btnMore = new ImageButton();
btnMore.ImageUrl = IMG_MORE;
btnMore.AlternateText = ALT_MORE;
btnMore.Click += new ImageClickEventHandler(MoreClicked);
Controls.Add(btnMore);
}
override protected void OnPreRender(EventArgs e) {
btnPrev.Visible = CurrentPageIndex > 0;
btnMore.Visible = CurrentPageIndex < PageCount;
}
override protected void Render(HtmlTextWriter writer) {
if (ItemCount == 0) {
writer.Write(emptyText);
return;
}
writer.Write(HTML1);
for (int i = 0, j = Controls.Count - 2; i < j; i++)
Controls[i].RenderControl(writer);
writer.Write(HTML2);
btnPrev.RenderControl(writer);
writer.Write(HTML3);
btnMore.RenderControl(writer);
writer.Write(HTML4);
}
} 未完待續(xù)