Silverlight的Data Bindings：Silverlight 與 ASP.NET Ajax
文/黃忠成
不可否認，對於網頁美工人員或是動畫設計師而言，Silverlight提供了Flash以外的一個畫布，令她們可盡情揮灑創意！但對於設計師而言，Silverlight如何結合資料庫來呈現資料則是更具吸引力的課題，很明顯的！Silverlight 1.0 RC與Silverlight 1.1並不支援Data Binding機制，而且目前對於中文顯示仍存在著問題(下載字型不算是個解法，因為有法律問題)，不過如果這個問題獲得解決，Silverlight結合資料庫後所呈現的效果，相信會給客戶完全不同的網頁操作感受，當然！前提得要Silverlight支援Data Bindings，否則一切都是紙上談兵罷了。要令Silverlight支援Data Bindings說來也不難，只要處理幾個關鍵問題即可。一、資料提供者為何？ASP.NET Ajax的PageMethods/Web Service可以勝任此工作，如下列程式片段所示。
|
private static DataTable BuildDataCache()
{
if (HttpRuntime.Cache["DataCache_Employees"] != null)
return HttpRuntime.Cache["DataCache_Employees"] as DataTable;
else
{
using (SqlConnection conn = new SqlConnection(ConfigurationManager.ConnectionStrings[
"NorthwindConnectionString"].ConnectionString))
{
SqlDataAdapter adapter = new SqlDataAdapter(
"SELECT * FROM Employees ORDER BY EmployeeID", conn);
DataTable table = new DataTable("Employees");
adapter.Fill(table);
HttpRuntime.Cache["DataCache_Employees"] = table;
return table;
}
}
}
[WebMethod]
public static Employee GetData(int index)
{
DataTable table = BuildDataCache();
return new Employee(table.DefaultView[index]);
}
[WebMethod]
public static int GetCount()
{
DataTable table = BuildDataCache();
return table.DefaultView.Count;
}
protected void Button1_Click(object sender, EventArgs e)
{
}
}
[Serializable]
public class Employee
{
[NonSerialized]
private DataRowView _rv = null;
public string EmployeeID
{
get
{
return (_rv.Row.IsNull("EmployeeID") ? string.Empty : _rv["EmployeeID"].ToString());
}
}
public string LastName
{
get
{
return (_rv.Row.IsNull("LastName") ? string.Empty : (string)_rv["LastName"]);
}
}
public string FirstName
{
get
{
return (_rv.Row.IsNull("FirstName") ? string.Empty : (string)_rv["FirstName"]);
}
}
public string Title
{
get
{
return (_rv.Row.IsNull("Title") ? string.Empty : (string)_rv["Title"]);
}
}
public string HireDate
{
get
{
return (_rv.Row.IsNull("HireDate") ?
string.Empty : ((DateTime)_rv["HireDate"]).ToShortDateString());
}
}
public Employee(DataRowView rv)
{
_rv = rv;
}
}
|
運用ASP.NET Ajax及JSON，我們可以輕易的用JavaScript來取得資料庫的資料，接著只要將資料設定給指定Silverlight控制項即可，這個工作可以簡單化也可以複雜化，簡單的作法是直接在JavaScript以findName來取得控制項，然後一一設定其屬性值。
|
handleLoad: function(plugIn, userContext, rootElement)
{
this.plugIn = plugIn;
this.dataContext = rootElement.children.getItem(0);
PageMethods.GetCount(this.OnSucceeded,this.OnFailed,this);
this.receiveData(this.currentDataIndex);
},
OnSucceeded: function(result, userContext, methodName)
{
if (methodName == "GetData")
{
userContext.displayData(result);
}
else if(methodName == "GetCount")
userContext.recordCount = result;
},
OnFailed:function(error, userContext, methodName)
{
if(error !== null)
{
alert(error.get_message());
}
},
displayData: function(data)
{
var idCtrl = this.dataContext.findName('txtEmployeeID');
var firstNameCtrl = this.dataContext.findName('txtLastName');
var lastNameCtrl = this.dataContext.findName('txtFirstName');
var titleCtrl = this.dataContext.findName('txtTitle');
var hireDateCtrl = this.dataContext.findName('txtHireDate');
var imgCtrl = this.dataContext.findName("imgPhoto");
idCtrl.text = data.EmployeeID;
firstNameCtrl.text = data.FirstName;
lastNameCtrl.text = data.LastName;
titleCtrl.text = data.Title;
hireDateCtrl.text = data.HireDate;
imgCtrl.source = "Default.aspx?ID="+idCtrl.text;
this.dataContext.findName("imgAnimation").begin();
}
|
這種做法的缺點是設計師得用JavaScript寫下許多程式碼。另一種做法是利用Silverlight控制項的Tag屬性，指定Binding Expression，然後於JavaScript中巡覽她們來一一指定值，如下列片段所示。
|
<Canvasxmlns="http://schemas.microsoft.com/client/2007"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
<CanvasName="DataDemo"Height="600"Width="800"Tag="BindingContext:GetData,GetCount">
<Canvas.Background>
<LinearGradientBrush>
<GradientStopColor="Yellow"Offset="0.0" />
<GradientStopColor="Orange"Offset="0.5" />
<GradientStopColor="Red"Offset="1.0" />
</LinearGradientBrush>
</Canvas.Background>
<TextBlockTag="BindingField:EmployeeID;BindingProperty:Text"Name="txtEmployeeID"Width="144"Height="24"Canvas.Left="166"Canvas.Top="23"Text="A00001"TextWrapping="Wrap"/>
<TextBlockTag="BindingField:LastName;BindingProperty:Text"Name="txtLastName"Width="320"Height="24"Canvas.Left="500"Canvas.Top="23"Text="Alean Company"TextWrapping="Wrap"/>
<TextBlockTag="BindingField:FirstName;BindingProperty:Text"Name="txtFirstName"Width="320"Height="24"Canvas.Left="166"Canvas.Top="72"Text="Jeffray"TextWrapping="Wrap"/>
<TextBlockTag="BindingField:Title;BindingProperty:Text"Name="txtTitle"Width="576"Height="24"Canvas.Left="166"Canvas.Top="122"Text="Taipen 101"TextWrapping="Wrap"/>
<TextBlockTag="BindingField:HireDate;BindingProperty:Text"Name="txtHireDate"Width="576"Height="24"Canvas.Left="166"Canvas.Top="171"Text="2005/3/4"TextWrapping="Wrap"/>
<ImageName="imgPhoto" Tag="BindingField:EmployeeID;BindingProperty:Source;Format:Default.aspx?ID={0}"Width="357"Height="206"Canvas.Left="400"Canvas.Top="301">
<Image.Triggers>
<EventTriggerRoutedEvent="Image.Loaded">
<BeginStoryboard>
<StoryboardName="imgAnimation">
<DoubleAnimation
Storyboard.TargetName="imgPhoto"
Storyboard.TargetProperty="Opacity"
From="0.0"To="1.0"Duration="0:0:6"/>
</Storyboard>
</BeginStoryboard>
</EventTrigger>
</Image.Triggers>
</Image>
<TextBlockName="txtLabel1"Width="114"Height="24"Canvas.Left="18"Canvas.Top="23"Text="Employee ID:"TextWrapping="Wrap"/>
<TextBlockName="txtLabel1_Copy"Width="120"Height="24"Canvas.Left="349"Canvas.Top="23"Text="Last Name:"TextWrapping="Wrap"/>
<TextBlockName="txtLabel1_Copy1"Width="130"Height="24"Canvas.Left="18"Canvas.Top="72"Text="First Name:"TextWrapping="Wrap"/>
<TextBlockName="txtLabel1_Copy2"Width="104"Height="24"Canvas.Left="18"Canvas.Top="122"Text="Title :"TextWrapping="Wrap"/>
<TextBlockName="txtLabel1_Copy3"Width="93"Height="24"Canvas.Left="18"Canvas.Top="171"Text="Hire Date:"TextWrapping="Wrap"/>
</Canvas>
</Canvas>
|
那如何解析Tag的Binding Expression並指定值呢？答案是利用Silverlight的JavaScript支援，一一巡覽所有控制項，一一解析Tag，然後再指定值。
|
/////////////////////////////////////////////////////////////////////////
// Silverlight Data Binding Helper 0.1
/////////////////////////////////////////////////////////////////////////
if (!window.SilverlightBinding)
window.SilverlightBinding = {};
SilverlightBinding.BindingData = function(ctrl,bindingExpression)
{
var bindings = bindingExpression.split(';');
this.bindingComplete = false;
this.ctrl = ctrl;
for(var i = 0; i < bindings.length; i++)
{
var temp = bindings[i].split(':');
if(temp.length != 2)
{
this.bindingComplete = false;
return;
}
if(temp[0] == 'BindingField')
this.bindingField = temp[1];
else if(temp[0] == 'BindingProperty')
this.bindingProperty = temp[1];
else if(temp[0] == 'Format')
this.format = temp[1];
}
this.bindingComplete = true;
}
SilverlightBinding.BindingData.prototype =
{
updateValue : function(dataItem)
{
if(this.bindingComplete)
{
if(this.format)
eval('this.ctrl.'+this.bindingProperty+
" = this.format.replace('{0}',dataItem."+this.bindingField+');');
else
eval('this.ctrl.'+this.bindingProperty+' = dataItem.'+this.bindingField+';');
}
}
}
SilverlightBinding.BindingContext = function(bindingContainer)
{
var parseBinding = bindingContainer.tag.split(':');
this.bindingComplete = false;
this.bindingContainer = bindingContainer;
this.bindingControls = new Array();
this.currentDataIndex = 0;
this.recordCount = 0;
if(parseBinding.length == 2 && parseBinding[0] == "BindingContext")
{
var bindingMethods = parseBinding[1].split(',');
if(bindingMethods.length == 2)
{
this.bindingMethod = bindingMethods[0];
this.bindingCountMethod = bindingMethods[1];
this.bindingComplete = true;
}
}
if(!this.bindingComplete) alert('ERROR,Binding Failed.');
}
SilverlightBinding.BindingContext.prototype =
{
_childWorker : function(parent,parseParent)
{
if(parent.tag && parent.tag != '')
{
if(parseParent)
{
var bindingData = new SilverlightBinding.BindingData(parent,parent.tag);
if(bindingData.bindingComplete)
{
this.bindingControls.length++;
this.bindingControls[this.bindingControls.length-1] = bindingData;
}
else
delete bindingData;
}
try
{
var temp = parent.children;
}
catch(err)
{
return;
}
for(var i = 0; i < parent.children.count; i++)
this._childWorker(parent.children.getItem(i),true);
}
},
initialize:function()
{
this._childWorker(this.bindingContainer,false);
this._receiveCount();
this._receiveData(0);
},
OnSucceeded: function(result, userContext, methodName)
{
if (methodName == userContext.bindingMethod)
{
for(var i = 0; i < userContext.bindingControls.length; i++)
userContext.bindingControls[i].updateValue(result);
}
else if(methodName == userContext.bindingCountMethod)
userContext.recordCount = result;
},
OnFailed:function(error, userContext, methodName)
{
if(error !== null)
{
alert(error.get_message());
}
},
_receiveData: function(index)
{
eval('PageMethods.'+this.bindingMethod+
'(index,this.OnSucceeded,this.OnFailed,this);');
},
_receiveCount: function()
{
eval('PageMethods.'+this.bindingCountMethod+
'(this.OnSucceeded,this.OnFailed,this);');
},
next:function()
{
if(this.currentDataIndex+1 >= this.recordCount)
return;
this._receiveData(++this.currentDataIndex);
},
prev:function()
{
if(this.currentDataIndex -1 < 0)
return;
this._receiveData(--this.currentDataIndex);
}
}
|
使用此JavaScript物件的方法很簡單，只要於handleLoad中建立此物件，然後將Silverlight的根控制項傳入即可。
|
handleLoad: function(plugIn, userContext, rootElement)
{
this.plugIn = plugIn;
this.dataContext = rootElement.children.getItem(0);
this.bindingContext =
new SilverlightBinding.BindingContext(rootElement.children.getItem(0));
this.bindingContext.initialize();
}
|
切換上下筆時也很簡單。
|
function Next()
{
window.Silverlight.current_DataContext.bindingContext.next();
window.Silverlight.current_DataContext.dataContext.findName("imgAnimation").begin();
}
function Prev()
{
window.Silverlight.current_DataContext.bindingContext.prev();
window.Silverlight.current_DataContext.dataContext.findName("imgAnimation").begin();
}
|
下圖為執行畫面。
看不到炫麗效果啊？哈~~~我承認，我的美工細胞粉差！
本例下載位址：
http://www.dreams.idv.tw/~code6421/files/SLDataDemo1.zip