asp.net 动态创建TextBox控件如何加载状态信息

接着上文Asp.net TextBox的TextChanged事件你真的清楚吗？这里我们来说说状态数据时如何加载的。
虽然在Control中有调用状态转存的方法，但是这里有一个判断条件 if (_controlState >= ControlState.ViewStateLoaded) 一般的get请求这里的条件是不满足的。

internal enum ControlState
{
    Constructed,
    FrameworkInitialized,
    ChildrenInitialized,
    Initialized,
    ViewStateLoaded,
    Loaded,
    PreRendered
}

我们知道在page的ProcessRequest中this.ControlState = ControlState.FrameworkInitialized; ProcessRequestMain方法中在Init后有调用this.InitRecursive(null);在这个方法里面有这么一句_controlState = ControlState.Initialized;，在LoadAllState()方法中有这么一句 base.LoadViewStateRecursive(second.Second);，而LoadViewStateRecursive中又有_controlState = ControlState.ViewStateLoaded这句带代码，所以我们在Page_load中动态条件控件时， if (_controlState >= ControlState.ViewStateLoaded)条件成立，如图：

所以在运行this.form1.Controls.Add(txt);这句以前，txt的值为demo1，

如图

但是运行以后之就发生变化了：

当然这里的txt.Text值也是我上次post过来的旧值，新值是在控件的LoadPostData方法中重新绑定。在默认的LoadViewStateRecursive方法中有一个很重要的判断

        internal void LoadViewStateRecursive(object savedState) {
            // nothing to do if we have no state
            if (savedState == null || flags[disableViewState])
                return;

。。。。。。。

_controlState = ControlState.ViewStateLoaded
}

大家看到我上面是一个CustTextBoxt : TextBox控件，如果我们直接添加TextBox控件的话，那么着这里的txt.Text一直都是demo1，可见控件动态添加的时候是否加载状态数据与状态数据的保存有关。而状态数据的保存主要就是SaveViewState完成的，这里我第一次post的时候SaveViewState返回数据：

所以第二次能取到上次post过来的数据。

其中与SaveViewState有关的方法主要有：

public class TextBox : WebControl, IPostBackDataHandler, IEditableTextControl {protected override object SaveViewState() {if (SaveTextViewState == false) {ViewState.SetItemDirty("Text", false);}return base.SaveViewState();}private bool SaveTextViewState {get {//// Must be saved when// 1. There is a registered event handler for SelectedIndexChanged// 2. Control is not enabled or visible, because the browser's post data will not include this control// 3. The instance is a derived instance, which might be overriding the OnTextChanged methodif (TextMode == TextBoxMode.Password) {return false;}if ((Events[EventTextChanged] != null) ||(IsEnabled == false) ||(Visible == false) ||(ReadOnly) ||(this.GetType() != typeof(TextBox))) {return true;}return false;}}}public class WebControl : Control, IAttributeAccessor {protected override object SaveViewState() {Pair myState = null;// Save values cached out of view stateif (_webControlFlags[disabledDirty]) {ViewState["Enabled"] = !flags[isWebControlDisabled];}if (ControlStyleCreated) {// the style shares the StateBag of its owner WebControl// call SaveViewState to let style participate in state management
                ControlStyle.SaveViewState();}object baseState = base.SaveViewState();object aState = null;if (attrState != null) {aState = attrState.SaveViewState();}if (baseState != null || aState != null) {myState = new Pair(baseState, aState);}return myState;}
}
public class Control : IComponent, IParserAccessor, IUrlResolutionService, IDataBindingsAccessor, IControlBuilderAccessor, IControlDesignerAccessor, IExpressionsAccessor {protected virtual object SaveViewState() {// Save values cached out of view stateif (flags[visibleDirty]) {ViewState["Visible"] = !flags[invisible];}if (flags[validateRequestModeDirty]) {ViewState["ValidateRequestMode"] = (int)ValidateRequestMode;}if (_viewState != null)return _viewState.SaveViewState();return null;}
}
public sealed class StateBag : IStateManager, IDictionary {internal object SaveViewState() {ArrayList data = null;if (bag.Count != 0) {IDictionaryEnumerator e = bag.GetEnumerator();while (e.MoveNext()) {StateItem item = (StateItem)(e.Value);if (item.IsDirty) {if (data == null) {data = new ArrayList();}
#if OBJECTSTATEFORMATTERdata.Add(new IndexedString((string)e.Key));
#elsedata.Add(e.Key);
#endifdata.Add(item.Value);}}}return data;}}