本篇体验扩展StringBuilder使之支持链式方法。
这里有一个根据键值集合生成select元素的方法。
private static string BuilderSelectBox(IDictionary<int, string> options, string id, bool includeUnknown) { var html = new StringBuilder(); html.AppendFormat("<select id="{0}" name="{0}">", id); html.AppendLine(); if(includeUnknown) { html.AppendLine(" <option>Unknown</option>"); } foreach(var opt in options) { html.AppendFormat(" <option value="{0}">{1}</option>", opt.Key, opt.Value); html.AppendLine(); } html.AppendLine("</select>"); return html.ToString(); }
以上,
html.AppendFormat("<select id="{0}" name="{0}">", id);
html.AppendLine();
可以对这两个语句封装,扩展StringBuilder。
改成
public static class StringBuilderExtensions { public static StringBuilder AppendFormattedLine(this StringBuilder @this, string format, prams object[] args) => @this.AppendFormat(format, args).AppendLine(); } private static string BuilderSelectBox(IDictionary<int, string> options, string id, bool includeUnknown) { var html = new StringBuilder() .AppendFormattedLine("<select id="{0}" name="{0}">", id); if(includeUnknown) { html.AppendLine(" <option>Unknown</option>"); } foreach(var opt in options) { html.AppendFormattedLine(" <option value="{0}">{1}</option>", opt.Key, opt.Value); html.AppendLine(); } html.AppendLine("</select>"); return html.ToString(); }
以上,
if(includeUnknown)
{
html.AppendLine(" <option>Unknown</option>");
}
可以对如上语句进行封装,继续扩展StringBuilder.
public static class StringBuilderExtensions { public static StringBuilder AppendFormattedLine(this StringBuilder @this, string format, prams object[] args) => @this.AppendFormat(format, args).AppendLine(); public static StringBuilder AppendLineWhen(this StringBuilder @this, Func<bool> predicate, string value) => predicate() ? @this.AppendLine(value) : @this; } private static string BuilderSelectBox(IDictionary<int, string> options, string id, bool includeUnknown) { var html = new StringBuilder() .AppendFormattedLine("<select id="{0}" name="{0}">", id) .AppendLineWhen(() => includeUnknown, " <option>Unknown</option>"); foreach(var opt in options) { html.AppendFormattedLine(" <option value="{0}">{1}</option>", opt.Key, opt.Value); } html.AppendLine("</select>"); return html.ToString(); }
或
public static class StringBuilderExtensions { public static StringBuilder AppendFormattedLine(this StringBuilder @this, string format, prams object[] args) => @this.AppendFormat(format, args).AppendLine(); public static StringBuilder AppendLineWhen(this StringBuilder @this, Func<bool> predicate, string value) => predicate() ? @this.AppendLine(value) : @this; public static StringBuilder AppendWhen(this StringBuilder @this, Func<bool> predicate, Func<StringBuilder, StringBuilder> fn) => predicate() ? fn(@this) : @this; } private static string BuilderSelectBox(IDictionary<int, string> options, string id, bool includeUnknown) { var html = new StringBuilder() .AppendFormattedLine("<select id="{0}" name="{0}">", id) .AppendWhen( () => includeUnknown, sb => sb.AppendLine(" <option>Unknown</option>") ); foreach(var opt in options) { html.AppendFormattedLine(" <option value="{0}">{1}</option>", opt.Key, opt.Value); } html.AppendLine("</select>"); return html.ToString(); }
以上,
foreach(var opt in options)
{
html.AppendFormattedLine(" <option value="{0}">{1}</option>", opt.Key, opt.Value);
}
对遍历语句进行封装,扩展StringBuilder,最终:
public static class StringBuilderExtensions { public static StringBuilder AppendFormattedLine(this StringBuilder @this, string format, prams object[] args) => @this.AppendFormat(format, args).AppendLine(); public static StringBuilder AppendLineWhen(this StringBuilder @this, Func<bool> predicate, string value) => predicate() ? @this.AppendLine(value) : @this; public static StringBuilder AppendWhen(this StringBuilder @this, Func<bool> predicate, Func<StringBuilder, StringBuilder> fn) => predicate() ? fn(@this) : @this; public static StringBuilder AppendSequence<T>(this StringBuilder @this, IEnumerable<T> seq, Func<StringBuilder, T, StringBuilder> fn) => seq.Aggregate(@this, fn); } private static string BuilderSelectBox(IDictionary<int, string> options, string id, bool includeUnknown) { var html = new StringBuilder() .AppendFormattedLine("<select id="{0}" name="{0}">", id) .AppendWhen( () => includeUnknown, sb => sb.AppendLine(" <option>Unknown</option>") ) .AppendSequence(options, (sb, opt) => sb.AppendFormattedLine(" <option value="{0}">{1}</option>", opt.Key, opt.Value)) .AppendLine("</select>") .ToString(); }