{"id":5011,"date":"2019-03-06T09:47:20","date_gmt":"2019-03-06T01:47:20","guid":{"rendered":"http:\/\/blog.qdac.cc\/?p=5011"},"modified":"2019-03-06T09:49:01","modified_gmt":"2019-03-06T01:49:01","slug":"qmathexpr%e4%b8%ba-qjson-%e5%a2%9e%e5%8a%a0-qmathexpr-%e6%94%af%e6%8c%81","status":"publish","type":"post","link":"https:\/\/blog.qdac.cc\/?p=5011","title":{"rendered":"[QMathExpr]\u4e3a QJson \u589e\u52a0 QMathExpr \u652f\u6301"},"content":{"rendered":"\n<blockquote class=\"wp-block-quote is-layout-flow wp-block-quote-is-layout-flow\"><p>QMathExpr \u53ef\u4ee5\u65b9\u4fbf\u7684\u5b9e\u73b0\u8868\u8fbe\u5f0f\u7684\u8ba1\u7b97\uff0c\u5c06\u5b83\u4e0e QJson \u7ed3\u5408\u5728\u4e00\u8d77\uff0c\u5c31\u53ef\u4ee5\u5bf9\u5185\u5bb9\u8fdb\u884c\u52a0\u5de5\u5904\u7406\uff0c\u4e3a\u7a0b\u5e8f\u7684\u5b9e\u73b0\u63d0\u4f9b\u66f4\u5927\u7684\u7075\u6d3b\u6027\u3002\u540c\u6837\u7684\uff0c\u4f60\u53ef\u4ee5\u540c\u6837\u5c06 QXML\/QMsgPack \u4e00\u6837\u5c01\u88c5\u4e0b\uff0c\u4e3a\u5176\u52a0\u4e0a QMathExpr \u7684\u652f\u6301\u3002<\/p><\/blockquote>\n\n\n\n<pre class=\"wp-block-code\"><code>TQJsonVarHelper = class helper for TQJson\n   private\n     procedure DoGetJsonVar(Sender: IQMathExpression; const AVarName: String;\n       var AVar: TQMathVar);\n     class procedure DoGetJsonValue(Sender: TObject; AVar: TQMathVar); static;\n     function GetAsExpression: Variant;\n   public\n     property AsExpression: Variant read GetAsExpression;\n   end;<\/code><\/pre>\n\n\n\n<pre class=\"wp-block-code\"><code>{ TQJsonVarHelper }\n class procedure TQJsonVarHelper.DoGetJsonValue(Sender: TObject;\n   AVar: TQMathVar);\n var\n   AItem: TQJson;\n begin\n   AItem := TQJson(AVar.Tag);\n   if Assigned(AItem) then\n     AVar.Value := AItem.AsVariant\n   else\n     AVar.Value := Unassigned;\n end;\n procedure TQJsonVarHelper.DoGetJsonVar(Sender: IQMathExpression;\n   const AVarName: String; var AVar: TQMathVar);\n var\n   AJson, AItem: TQJson;\n begin\n   AJson := TQJson(Sender.Tag);\n   if StartWithW(PWideChar(AVarName), '$', false) then\n     AItem := AJson.ItemByPath(RightStrW(AVarName,\n       Length(AVarName) - 1, false))\n   else\n     AItem := AJson.ItemByPath(AVarName);\n   if Assigned(AItem) then\n   begin\n     AVar := Sender.Add(AVarName, 0, 0, DoGetJsonValue);\n     AVar.Tag := AItem;\n   end;\n end;\n function TQJsonVarHelper.GetAsExpression: Variant;\n var\n   AExpr: IQMathExpression;\n begin\n   AExpr := TQMathExpression.Create;\n   AExpr.OnLookupMissed := DoGetJsonVar;\n   AExpr.Tag := Parent;\n   Result := AExpr.Eval(Value);\n end;<\/code><\/pre>\n\n\n\n<p>\u8c03\u7528\u793a\u4f8b\uff1a<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>var\n   AJsonVars:TQJson;\nbegin\n   AJsonVars := TQJson.Create;\n   AJsonVars.Parse('{\"a\":{\"b\":1,\"c\":2},\"f\":20}');\n   \/\/ d\u7684\u503c\u901a\u8fc7\u8868\u8fbe\u5f0f\u8ba1\u7b97\u8d4b\u503c\n   AJsonVars.Add('d').AsString := 'f+$a.c';\n   ShowMessage(VarToStr(AJsonVars.ItemByName('d').AsExpression));<\/code><\/pre>\n\n\n\n<p><\/p>\n","protected":false},"excerpt":{"rendered":"<p>QMathExpr \u53ef\u4ee5\u65b9\u4fbf\u7684\u5b9e\u73b0\u8868\u8fbe\u5f0f [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"site-sidebar-layout":"default","site-content-layout":"","ast-site-content-layout":"default","site-content-style":"default","site-sidebar-style":"default","ast-global-header-display":"","ast-banner-title-visibility":"","ast-main-header-display":"","ast-hfb-above-header-display":"","ast-hfb-below-header-display":"","ast-hfb-mobile-header-display":"","site-post-title":"","ast-breadcrumbs-content":"","ast-featured-img":"","footer-sml-layout":"","ast-disable-related-posts":"","theme-transparent-header-meta":"","adv-header-id-meta":"","stick-header-meta":"","header-above-stick-meta":"","header-main-stick-meta":"","header-below-stick-meta":"","astra-migrate-meta-layouts":"default","ast-page-background-enabled":"default","ast-page-background-meta":{"desktop":{"background-color":"var(--ast-global-color-4)","background-image":"","background-repeat":"repeat","background-position":"center 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