asp.net 動態創建TextBox控件 如何加載狀態信息

接著上文Asp.net TextBox的TextChanged事件你真的清楚嗎？ 這里我們來說說狀態數據時如何加載的。
雖然在Control中有調用狀態轉存的方法，但是這里有一個判斷條件 if (_controlState >= ControlState.ViewStateLoaded)? 一般的get請求這里的條件是不滿足的。

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

我們知道在page的ProcessRequest中this.ControlState = ControlState.FrameworkInitialized; ProcessRequestMain方法中在Init后有調用this.InitRecursive(null);在這個方法里面有這么一句_controlState = ControlState.Initialized;，在LoadAllState()方法中有這么一句?base.LoadViewStateRecursive(second.Second);，而LoadViewStateRecursive中又有_controlState = ControlState.ViewStateLoaded這句帶代碼，所以我們在Page_load中動態條件控件時， if (_controlState >= ControlState.ViewStateLoaded)條件成立，如圖：

所以在運行this.form1.Controls.Add(txt);這句以前，txt的值為demo1，

如圖

但是運行以后之就發生變化了：

當然這里的txt.Text值也是我上次post過來的舊值，新值是在控件的LoadPostData方法中重新綁定。在默認的LoadViewStateRecursive方法中有一個很重要的判斷

??????? 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個CustTextBoxt : TextBox控件，如果我們直接添加TextBox控件的話，那么著這里的txt.Text一直都是demo1，可見控件動態添加的時候是否加載狀態數 據與狀態數據的保存有關。而狀態數據的保存主要就是SaveViewState完成的，這里我第一次post的時候SaveViewState返回數據：

所以第二次能取到上次post過來的數據。

其中與SaveViewState有關的方法主要有：

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;}}

到這里我們知道保存狀態信息主要是在StateBag 的SaveViewState方法中，這里有一個檢查? if (item.IsDirty) ，在TextBox的SaveViewState方法中有一個判斷

??? if (SaveTextViewState == false) {
??????????????? ViewState.SetItemDirty("Text", false);
??????????? }?

與它的SaveTextViewState 屬性有關。

那么我們可以總結一下：動態創建的控件默認是在被添加的時候加載器狀態數據，如果是靜態添加的數據那就是LoadAllState來處理狀態數據的加載。狀態數據的加載與控件的SaveViewState密切相關，如果該方法的返回值為null既沒有狀態信息，那也不需要加載什么狀態信息了。