asp.net 动态创建TextBox控件 怎么加载状态信息

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 method
 
                if (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 state
            if (_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 state
            if (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 OBJECTSTATEFORMATTER
                        data.Add(new IndexedString((string)e.Key));
#else
                        data.Add(e.Key);
#endif
                        data.Add(item.Value);
                    }
                }
            }

            return data;
        }
    }

到这里我们知道保存状态信息主要是在StateBag 的SaveViewState方法中，这里有一个检查  if (item.IsDirty) ，在TextBox的SaveViewState方法中有一个判断

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

与它的SaveTextViewState 属性有关。

那么我们可以总结一下：动态创建的控件默认是在被添加的时候加载器状态数据，如果是静态添加的数据那就是LoadAllState来处理状态数据的加载。状态数据的加载与控件的SaveViewState密切相关，如果该方法的返回值为null既没有状态信息，那也不需要加载什么状态信息了。