选项卡上缺少UI控件，为什么调用HandleNeeded可以解决该问题? [英] Missing UI Control on tab, why calling HandleNeeded fixes it?

问题描述

我有一个UI对象附加到一个选项卡，该选项卡仅在与程序进行一定顺序的交互时才会丢失，如果丢失，关闭程序将导致AV和无效窗口句柄的错误.当我试图找出原因时，我发现在开始时调用其.Handle或.HandleNeeded可以解决此问题.但这并不能回答为什么它可以解决问题.

I had one UI object attached to a tab that will go missing only under a certain sequence of interaction with the program, and if it's missing, closing the program will result in AV and error of Invalid Window Handle. As I was trying to find out why, I found that calling its .Handle or .HandleNeeded at the start will fix the problem. But that doesn't answer why does it fix the problem.

所以我希望知道这是普遍现象吗?有人遇到过这个奇怪的错误吗?知道原因吗?

So I would hope to know that is this common? Has anyone encountered this strange bug before? And know the reason?

推荐答案

如果使用的是TabControl，则Delphi仅在需要页面时才为每个页面创建控件(出于速度和资源使用的原因).尝试访问未显示的页面上的控件将导致问题，除非您调用.HandleNeeded.调用.HandleNeeded告诉Delphi您现在需要手柄，并消除了问题.

If you're using a TabControl, Delphi only creates the controls for each page when the page is needed (for speed and resource usage reasons). Trying to access controls on a page that hasn't been shown will cause issues, unless you call .HandleNeeded. The call to .HandleNeeded tells Delphi you need the handle now, and eliminates the problem.

这不是错误，顺便说一句.如上所述，这是一个有意的设计决策，目的是提高速度并最大程度地减少资源使用.

It's not a bug, BTW. It's an intentional design decision, for speed and minimization of resource usage as I mentioned above.

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