asp.net mvc源码分析-EditorFor

在我们的mvc日常开发会经常遇到什么LabelFor、EditorFor、Editor等等，这个扩展方法有很多是相似的。这里我们以EditorFor来说说吧，我觉得这个相对要复杂一点。

首先我们来看看EditorFor的定义：

public static MvcHtmlString EditorFor<TModel,
TValue>(this HtmlHelper<TModel> html,
Expression<Func<TModel, TValue>> expression, object
additionalViewData) {

return TemplateHelpers.TemplateFor(html, expression, null /* templateName */, null /* htmlFieldName */, DataBoundControlMode.Edit, additionalViewData);

}

虽然EditorFor有很多定义，但是实际上都是调用 TemplateHelpers.TemplateFor方法。

internal static MvcHtmlString TemplateFor<TContainer, TValue>(this HtmlHelper<TContainer> html, Expression<Func<TContainer, TValue>> expression,

string templateName, string htmlFieldName, DataBoundControlMode mode,

object additionalViewData) {

return MvcHtmlString.Create(TemplateFor(html, expression, templateName, htmlFieldName, mode, additionalViewData, TemplateHelper));

}

现在大家应该知道TemplateFor方法的主要参数都有哪些了吧，但是在实际开发中我们的templateName、htmlFieldName、additionalViewData通常都是null，mode是DataBoundControlMode.Edit

我们还是举一个例子来说说吧：

public class UserInfo

{

[StringLength(100, MinimumLength = 10)]

[Required]

public string UserName { set; get; }

}

@Html.EditorFor(model => model.UserName)

这个代码是不是很简单。

现在我们来看看TemplateFor的实现

return templateHelper(html,

ModelMetadata.FromLambdaExpression(expression, html.ViewData),

htmlFieldName ?? ExpressionHelper.GetExpressionText(expression),

templateName,

mode,

additionalViewData);

首先我们来看看 ModelMetadata.FromLambdaExpression(expression, html.ViewData)这句是如何获取ModelMetadata的，具体实现如下：

public static ModelMetadata FromLambdaExpression<TParameter, TValue>(Expression<Func<TParameter, TValue>> expression,
ViewDataDictionary<TParameter> viewData) {
if (expression == null) {
throw new ArgumentNullException("expression");
}
if (viewData == null) {
throw new ArgumentNullException("viewData");
}

string propertyName = null;
Type containerType = null;
bool legalExpression = false;

// Need to verify the expression is valid; it needs to at least end in something
// that we can convert to a meaningful string for model binding purposes

switch (expression.Body.NodeType) {
// ArrayIndex always means a single-dimensional indexer; multi-dimensional indexer is a method call to Get()
case ExpressionType.ArrayIndex:
legalExpression = true;
break;

// Only legal method call is a single argument indexer/DefaultMember call
case ExpressionType.Call:
legalExpression = ExpressionHelper.IsSingleArgumentIndexer(expression.Body);
break;

// Property/field access is always legal
case ExpressionType.MemberAccess:
MemberExpression memberExpression = (MemberExpression)expression.Body;
propertyName = memberExpression.Member is PropertyInfo ? memberExpression.Member.Name : null;
containerType = memberExpression.Expression.Type;
legalExpression = true;
break;

// Parameter expression means "model => model", so we delegate to FromModel
case ExpressionType.Parameter:
return FromModel(viewData);
}

if (!legalExpression) {
throw new InvalidOperationException(MvcResources.TemplateHelpers_TemplateLimitations);
}

TParameter container = viewData.Model;
Func<object> modelAccessor = () => {
try {
return CachedExpressionCompiler.Process(expression)(container);
}
catch (NullReferenceException) {
return null;
}
};

return GetMetadataFromProvider(modelAccessor, typeof(TValue), propertyName, containerType);
}

如果我们调用的是Editor那么之力调用就是FromStringExpression方法而不是FromLambdaExpression方法，这2个方法相差不大。我们还是来看看FromLambdaExpression这个方法吧：



看了这张图 那么 return GetMetadataFromProvider(modelAccessor, typeof(TValue), propertyName, containerType);这句代码里面的参数相信大家都应该是到了吧。

propertyName=“UserName” containerType=MvcApp.Controllers.UserInfo，modelAccessor就是创建一个实例，实例的创建是通过 model => model.UserName这句。至于GetMetadataFromProvider这个方法就没什么好讲的了，前面的文章已经讲过了，它实际是创建 了一个DataAnnotationsModelMetadata实例。

至于ExpressionHelper.GetExpressionText(expression)这句说白了默认就是返回一个属性名称，具体实现：

public static string GetExpressionText(LambdaExpression expression) {
// Split apart the expression string for property/field accessors to create its name
Stack<string> nameParts = new Stack<string>();
Expression part = expression.Body;

while (part != null) {
if (part.NodeType == ExpressionType.Call) {
MethodCallExpression methodExpression = (MethodCallExpression)part;

if (!IsSingleArgumentIndexer(methodExpression)) {
break;
}

nameParts.Push(
GetIndexerInvocation(
methodExpression.Arguments.Single(),
expression.Parameters.ToArray()
)
);

part = methodExpression.Object;
}
else if (part.NodeType == ExpressionType.ArrayIndex) {
BinaryExpression binaryExpression = (BinaryExpression)part;

nameParts.Push(
GetIndexerInvocation(
binaryExpression.Right,
expression.Parameters.ToArray()
)
);

part = binaryExpression.Left;
}
else if (part.NodeType == ExpressionType.MemberAccess) {
MemberExpression memberExpressionPart = (MemberExpression)part;
nameParts.Push("." + memberExpressionPart.Member.Name);
part = memberExpressionPart.Expression;
}
else if (part.NodeType == ExpressionType.Parameter) {
// Dev10 Bug #907611
// When the expression is parameter based (m => m.Something...), we'll push an empty
// string onto the stack and stop evaluating. The extra empty string makes sure that
// we don't accidentally cut off too much of m => m.Model.
nameParts.Push(String.Empty);
part = null;
}
else {
break;
}
}

// If it starts with "model", then strip that away
if (nameParts.Count > 0 && String.Equals(nameParts.Peek(), ".model", StringComparison.OrdinalIgnoreCase)) {
nameParts.Pop();
}

if (nameParts.Count > 0) {
return nameParts.Aggregate((left, right) => left + right).TrimStart('.');
}

return String.Empty;
}

这里的循环执行两次，第一次是执行

else if (part.NodeType == ExpressionType.MemberAccess) {

MemberExpression memberExpressionPart = (MemberExpression)part;

nameParts.Push("." + memberExpressionPart.Member.Name);

part = memberExpressionPart.Expression;

}

第二次执行

else if (part.NodeType == ExpressionType.Parameter) {

// Dev10 Bug #907611

// When the expression is parameter based (m => m.Something...), we'll push an empty

// string onto the stack and stop evaluating. The extra empty string makes sure that

// we don't accidentally cut off too much of m => m.Model.

nameParts.Push(String.Empty);

part = null;

}

当然这个方法默认的返回结果这里就是UserName了,它默认就是生成html是的id和name属性的值。

现在我们再来看看TemplateHelper方法了

internal static string TemplateHelper(HtmlHelper html, ModelMetadata metadata, string htmlFieldName, string templateName, DataBoundControlMode mode, object additionalViewData, ExecuteTemplateDelegate executeTemplate) {
// TODO: Convert Editor into Display if model.IsReadOnly is true? Need to be careful about this because
// the Model property on the ViewPage/ViewUserControl is get-only, so the type descriptor automatically
// decorates it with a [ReadOnly] attribute...

if (metadata.ConvertEmptyStringToNull && String.Empty.Equals(metadata.Model)) {
metadata.Model = null;
}

object formattedModelValue = metadata.Model;
if (metadata.Model == null && mode == DataBoundControlMode.ReadOnly) {
formattedModelValue = metadata.NullDisplayText;
}

string formatString = mode == DataBoundControlMode.ReadOnly ? metadata.DisplayFormatString : metadata.EditFormatString;
if (metadata.Model != null && !String.IsNullOrEmpty(formatString)) {
formattedModelValue = String.Format(CultureInfo.CurrentCulture, formatString, metadata.Model);
}

// Normally this shouldn't happen, unless someone writes their own custom Object templates which
// don't check to make sure that the object hasn't already been displayed
object visitedObjectsKey = metadata.Model ?? metadata.RealModelType;
if (html.ViewDataContainer.ViewData.TemplateInfo.VisitedObjects.Contains(visitedObjectsKey)) {    // DDB #224750
return String.Empty;
}

ViewDataDictionary viewData = new ViewDataDictionary(html.ViewDataContainer.ViewData) {
Model = metadata.Model,
ModelMetadata = metadata,
TemplateInfo = new TemplateInfo {
FormattedModelValue = formattedModelValue,
HtmlFieldPrefix = html.ViewContext.ViewData.TemplateInfo.GetFullHtmlFieldName(htmlFieldName),
VisitedObjects = new HashSet<object>(html.ViewContext.ViewData.TemplateInfo.VisitedObjects),    // DDB #224750
}
};

if (additionalViewData != null) {
foreach (KeyValuePair<string, object> kvp in new RouteValueDictionary(additionalViewData)) {
viewData[kvp.Key] = kvp.Value;
}
}

viewData.TemplateInfo.VisitedObjects.Add(visitedObjectsKey);    // DDB #224750

return executeTemplate(html, viewData, templateName, mode, GetViewNames, GetDefaultActions);
}

这个方法其实也很简单，获取当前model的值，以及呈现html的format格式，最后这里从新创建了一个ViewDataDictionary实例 viewData，并且把参数中的additionalViewData也合并到这个viewData中来，把当前的值 （visitedObjectsKey也就是最后呈现给textbox的value）给添加到viewData的VisitedObjects属性中。最 后再调用

return executeTemplate(html, viewData, templateName, mode, GetViewNames, GetDefaultActions);方法。

那么现在我们应该看看ExecuteTemplate方法了：

internal static string ExecuteTemplate(HtmlHelper html, ViewDataDictionary viewData, string templateName, DataBoundControlMode mode, GetViewNamesDelegate getViewNames, GetDefaultActionsDelegate getDefaultActions) {
Dictionary<string, ActionCacheItem> actionCache = GetActionCache(html);
Dictionary<string, Func<HtmlHelper, string>> defaultActions = getDefaultActions(mode);
string modeViewPath = modeViewPaths[mode];

foreach (string viewName in getViewNames(viewData.ModelMetadata, templateName, viewData.ModelMetadata.TemplateHint, viewData.ModelMetadata.DataTypeName)) {
string fullViewName = modeViewPath + "/" + viewName;
ActionCacheItem cacheItem;

if (actionCache.TryGetValue(fullViewName, out cacheItem)) {
if (cacheItem != null) {
return cacheItem.Execute(html, viewData);
}
}
else {
ViewEngineResult viewEngineResult = ViewEngines.Engines.FindPartialView(html.ViewContext, fullViewName);
if (viewEngineResult.View != null) {
actionCache[fullViewName] = new ActionCacheViewItem { ViewName = fullViewName };

using (StringWriter writer = new StringWriter(CultureInfo.InvariantCulture)) {
viewEngineResult.View.Render(new ViewContext(html.ViewContext, viewEngineResult.View, viewData, html.ViewContext.TempData, writer), writer);
return writer.ToString();
}
}

Func<HtmlHelper, string> defaultAction;
if (defaultActions.TryGetValue(viewName, out defaultAction)) {
actionCache[fullViewName] = new ActionCacheCodeItem { Action = defaultAction };
return defaultAction(MakeHtmlHelper(html, viewData));
}

actionCache[fullViewName] = null;
}
}

throw new InvalidOperationException(
String.Format(
CultureInfo.CurrentCulture,
MvcResources.TemplateHelpers_NoTemplate,
viewData.ModelMetadata.RealModelType.FullName
)
);
}

这里的GetActionCache方法很简单就是从当前的context.Items中获取一个字典数据，如果没有就实例化一个然后加入到context.Items中。GetDefaultActions方法也很简单

internal static Dictionary<string, Func<HtmlHelper, string>> GetDefaultActions(DataBoundControlMode mode) {

return mode == DataBoundControlMode.ReadOnly ? defaultDisplayActions : defaultEditorActions;

}

其中GetViewNames就是获取view的名称的一个方法：

internal static IEnumerable<string> GetViewNames(ModelMetadata metadata, params string[] templateHints) {
foreach (string templateHint in templateHints.Where(s => !String.IsNullOrEmpty(s))) {
yield return templateHint;
}

// We don't want to search for Nullable<T>, we want to search for T (which should handle both T and Nullable<T>)
Type fieldType = Nullable.GetUnderlyingType(metadata.RealModelType) ?? metadata.RealModelType;

// TODO: Make better string names for generic types
yield return fieldType.Name;

if (!metadata.IsComplexType) {
yield return "String";
}
else if (fieldType.IsInterface) {
if (typeof(IEnumerable).IsAssignableFrom(fieldType)) {
yield return "Collection";
}

yield return "Object";
}
else {
bool isEnumerable = typeof(IEnumerable).IsAssignableFrom(fieldType);

while (true) {
fieldType = fieldType.BaseType;
if (fieldType == null)
break;

if (isEnumerable && fieldType == typeof(Object)) {
yield return "Collection";
}

yield return fieldType.Name;
}
}
}

默认返回参数顺序是templateHints中的view，其次就是根据参数 数据类型返回相应的默认view。我这里返回的是String。

那么现在我们回到ExecuteTemplate方法中来，

string fullViewName = modeViewPath + "/" + viewName;这句就是已经找到我们的view了，如果我们先前actionCache中包含该key就直接执行该view并返回，其次通过 ViewEngines.Engines.FindPartialView来找该view，如果找到则输出该view并返回。否则调用默认的处理方式

if (defaultActions.TryGetValue(viewName, out defaultAction)) {

actionCache[fullViewName] = new ActionCacheCodeItem { Action = defaultAction };

return defaultAction(MakeHtmlHelper(html, viewData));

}

这里的defaultAction对应则DefaultDisplayTemplates.StringTemplate，因为我的
viewName是String，这里的MakeHtmlHelper方法是根据当前的ViewContext和viewData从新实例化一个
HtmlHelper。

DefaultEditorTemplates.StringTemplate方法非常简单：

return html.TextBox(String.Empty,

html.ViewContext.ViewData.TemplateInfo.FormattedModelValue,

CreateHtmlAttributes("text-box single-line")).ToHtmlString();

它里面主要是调用TextBox方法：

public static MvcHtmlString TextBox(this HtmlHelper htmlHelper,
string name, object value, IDictionary<string, object>
htmlAttributes) {

return InputHelper(htmlHelper, InputType.Text, null, name,
value, (value == null) /* useViewData */, false /* isChecked */, true /*
setId */, true /* isExplicitValue */, htmlAttributes);

}

private static MvcHtmlString InputHelper(HtmlHelper htmlHelper, InputType inputType, ModelMetadata metadata, string name, object value, bool useViewData, bool isChecked, bool setId, bool isExplicitValue, IDictionary<string, object> htmlAttributes) {
string fullName = htmlHelper.ViewContext.ViewData.TemplateInfo.GetFullHtmlFieldName(name);
if (String.IsNullOrEmpty(fullName)) {
throw new ArgumentException(MvcResources.Common_NullOrEmpty, "name");
}

TagBuilder tagBuilder = new TagBuilder("input");
tagBuilder.MergeAttributes(htmlAttributes);
tagBuilder.MergeAttribute("type", HtmlHelper.GetInputTypeString(inputType));
tagBuilder.MergeAttribute("name", fullName, true);

string valueParameter = Convert.ToString(value, CultureInfo.CurrentCulture);
bool usedModelState = false;

switch (inputType) {
case InputType.CheckBox:
bool? modelStateWasChecked = htmlHelper.GetModelStateValue(fullName, typeof(bool)) as bool?;
if (modelStateWasChecked.HasValue) {
isChecked = modelStateWasChecked.Value;
usedModelState = true;
}
goto case InputType.Radio;
case InputType.Radio:
if (!usedModelState) {
string modelStateValue = htmlHelper.GetModelStateValue(fullName, typeof(string)) as string;
if (modelStateValue != null) {
isChecked = String.Equals(modelStateValue, valueParameter, StringComparison.Ordinal);
usedModelState = true;
}
}
if (!usedModelState && useViewData) {
isChecked = htmlHelper.EvalBoolean(fullName);
}
if (isChecked) {
tagBuilder.MergeAttribute("checked", "checked");
}
tagBuilder.MergeAttribute("value", valueParameter, isExplicitValue);
break;
case InputType.Password:
if (value != null) {
tagBuilder.MergeAttribute("value", valueParameter, isExplicitValue);
}
break;
default:
string attemptedValue = (string)htmlHelper.GetModelStateValue(fullName, typeof(string));
tagBuilder.MergeAttribute("value", attemptedValue ?? ((useViewData) ? htmlHelper.EvalString(fullName) : valueParameter), isExplicitValue);
break;
}

if (setId) {
tagBuilder.GenerateId(fullName);
}

// If there are any errors for a named field, we add the css attribute.
ModelState modelState;
if (htmlHelper.ViewData.ModelState.TryGetValue(fullName, out modelState)) {
if (modelState.Errors.Count > 0) {
tagBuilder.AddCssClass(HtmlHelper.ValidationInputCssClassName);
}
}

tagBuilder.MergeAttributes(htmlHelper.GetUnobtrusiveValidationAttributes(name, metadata));

if (inputType == InputType.CheckBox) {
// Render an additional <input type="hidden".../> for checkboxes. This
// addresses scenarios where unchecked checkboxes are not sent in the request.
// Sending a hidden input makes it possible to know that the checkbox was present
// on the page when the request was submitted.
StringBuilder inputItemBuilder = new StringBuilder();
inputItemBuilder.Append(tagBuilder.ToString(TagRenderMode.SelfClosing));

TagBuilder hiddenInput = new TagBuilder("input");
hiddenInput.MergeAttribute("type", HtmlHelper.GetInputTypeString(InputType.Hidden));
hiddenInput.MergeAttribute("name", fullName);
hiddenInput.MergeAttribute("value", "false");
inputItemBuilder.Append(hiddenInput.ToString(TagRenderMode.SelfClosing));
return MvcHtmlString.Create(inputItemBuilder.ToString());
}

return tagBuilder.ToMvcHtmlString(TagRenderMode.SelfClosing);
}

这里的InputHelper是真正生成html字符串的地方。这个方法整体比较好理解，不过要注意这个方法里面有这么一句

tagBuilder.MergeAttributes(htmlHelper.GetUnobtrusiveValidationAttributes(name, metadata));

这句就是处理对象上面的那些验证属性，效果如图：



我想大家到这里应该对EditorFor方法有个了解了吧，感觉很是复杂。