| ASP.NET2.0服务器控件之类型化样式属性 |
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| 来源:天极yesky 作者: 加入时间：2006-10-27 访问次数:4 [大 中 小] |
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如上代码所示，MyPanel继承自WebControl基类，其中定义了3个属性BackImageUrl、HorizontalAlign和Wrap。关于这3个属性的说明，读者可参考前面的内容。另外，MyPanel重写了CreateControlStyle方法，返回一个MyPanelStyle对象。这样返回的MyPanelStyle实例间接的赋值给ControlStyle属性。这种实现方法的原因是由于ControlStyle属性是只读属性，且它的访问操作需要调用CreateControlStyle方法时间接进行设置。需要读者注意的是，CreateControlStyle将MyPanel控件的ViewState传递给MyPanelStyle的构造函数。当在CreateControlStyle中为控件创建新样式时，必须将控件的ViewState传给Style构造函数，那么样式对象则使用和控件相同的StateBag。
下面列举了实现MyPanelStyle类的源代码，它们来自MyPanelStyle.cs文件。
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Text;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
namespace WebControlLibrary{
public class MyPanelStyle : Style {
// 定义内部常量
internal const int PROP_BACKIMAGEURL = 1;
internal const int PROP_HORIZONTALALIGN = 2;
internal const int PROP_WRAP = 3;
//构造函数一
public MyPanelStyle() { }
// 构造函数二
public MyPanelStyle(StateBag bag) : base(bag) { }
// 创建BackImageUrl属性
[ Bindable(true), Category("Appearance"), DefaultValue(""), Description("背景图片的URL"), NotifyParentProperty(true) ]
public virtual string BackImageUrl {
get {
if (IsSet(PROP_BACKIMAGEURL)) {
return (string)ViewState["BackImageUrl"];
}
return String.Empty;
}
set {
ViewState["BackImageUrl"] = value;
}
}
// 实现HorizonalAlign属性
[ Bindable(true), Category("Layout"), DefaultValue(HorizontalAlign.NotSet), Description("所添加内容的水平对其方式"), NotifyParentProperty(true) ]
public virtual HorizontalAlign HorizonalAlign {
get {
if (IsSet(PROP_HORIZONTALALIGN)) {
return (HorizontalAlign)ViewState["HorizontalAlign"];
}
return HorizontalAlign.NotSet;
}
set {
if (value ＜ HorizontalAlign.NotSet || value ＞ HorizontalAlign.Justify) {
throw new ArgumentOutOfRangeException("value");
}
ViewState["HorizontalAlign"] = value;
}
}
// 实现IsEmpty
protected new internal bool IsEmpty {
get {
return base.IsEmpty && !IsSet(PROP_BACKIMAGEURL) && !IsSet(PROP_HORIZONTALALIGN) && !IsSet(PROP_WRAP);
}
}
//实现Wrap属性
[ Bindable(true), Category("Layout"), DefaultValue(true), Description("是否允许对所添加的内容换行"), NotifyParentProperty(true) ]
public virtual bool Wrap {
get {
if (IsSet(PROP_WRAP)) { return (bool)ViewState["Wrap"]; }
return true;
}
set { ViewState["Wrap"] = value; }
}
//辅助方法IsSet
internal bool IsSet(int propNumber) {
string key = null;
switch (propNumber) {
case PROP_BACKIMAGEURL: key = "BackImageUrl";
break;
case PROP_HORIZONTALALIGN: key = "HorizontalAlign";
break;
case PROP_WRAP: key = "Wrap";
break;
}
if (key != null) {
return ViewState[key] != null;
}
return false;
}
//重写AddAttributesToRender方法
public override void AddAttributesToRender(HtmlTextWriter writer, WebControl owner) {
if (IsSet(PROP_BACKIMAGEURL)) {
string s = BackImageUrl;
if (s.Length ＞ 0) {
if (owner != null) {
s = owner.ResolveUrl(s);
}
writer.AddStyleAttribute(HtmlTextWriterStyle.BackgroundImage, "url(" + s + ")");
}
}
if (IsSet(PROP_HORIZONTALALIGN)) {
System.Web.UI.WebControls.HorizontalAlign hAlign = this.HorizonalAlign;
if (hAlign != System.Web.UI.WebControls.HorizontalAlign.NotSet) {
TypeConverter hac = TypeDescriptor.GetConverter(typeof(HorizontalAlign));
writer.AddAttribute(HtmlTextWriterAttribute.Align, hac.ConvertToInvariantString(hAlign));
}
}
if (IsSet(PROP_WRAP)) {
bool wrap = Wrap;
if (!Wrap) {
writer.AddAttribute(HtmlTextWriterAttribute.Nowrap, "nowwrap");
}
}
base.AddAttributesToRender(writer, owner);
}
//重写CopyFrom方法
public override void CopyFrom(Style s) {
if (s != null) {
base.CopyFrom(s);
if (s is MyPanelStyle) {
MyPanelStyle mps = (MyPanelStyle)s;
if (!mps.IsEmpty) {
if (mps.IsSet(PROP_BACKIMAGEURL))
this.BackImageUrl = mps.BackImageUrl;
if (mps.IsSet(PROP_HORIZONTALALIGN))
this.HorizonalAlign = mps.HorizonalAlign;
if (mps.IsSet(PROP_WRAP))
this.Wrap = mps.Wrap;
}
}
}
}
// 重写MergeWith方法
public override void MergeWith(Style s) {
if (s != null) {
if (IsEmpty) {
CopyFrom(s);
return;
}
base.MergeWith(s);
if (s is MyPanelStyle) {
MyPanelStyle mps = (MyPanelStyle)s;
if (!mps.IsEmpty) {
if (mps.IsSet(PROP_BACKIMAGEURL) && !this.IsSet(PROP_BACKIMAGEURL))
this.BackImageUrl = mps.BackImageUrl;
if (mps.IsSet(PROP_HORIZONTALALIGN) && !this.IsSet(PROP_HORIZONTALALIGN))
this.HorizonalAlign = mps.HorizonalAlign;
if (mps.IsSet(PROP_WRAP) && !this.IsSet(PROP_WRAP))
this.Wrap = mps.Wrap;
}
}
}
}
//重写Reset方法
public override void Reset() {
base.Reset();
if (IsEmpty) return;
if (IsSet(PROP_BACKIMAGEURL))
ViewState.Remove("BackImageUrl");
if (IsSet(PROP_HORIZONTALALIGN))
ViewState.Remove("HorizontalAlign");
if (IsSet(PROP_WRAP)) ViewState.Remove("Wrap");
}
}
} |
下面列举了MyPanelStyle类图。
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