无法设置Fire Monkey Form属性 [英] Can't set Fire Monkey Form property

问题描述

我正在尝试在Fire Monkey应用程序的程序源文件中初始化表单属性，并且会引发异常.这是代码:

I am trying to initialize form properties in the program source file in a Fire Monkey application and it throws an exception. Here is the code:

uses
    System.StartUpCopy,
    FMX.Forms,
    uMainForm in 'Units\uMainForm.pas' {MainForm},
    UDataModule in 'Units\UDataModule.pas' {DataMod: TDataModule},
    DataHelperClasses in 'Units\DataHelperClasses.pas',
    EXDIntf in 'Units\EXDIntf.pas',
    Exd in 'Units\Exd.pas';

    {$R *.res}
    var
      ViewModel: TEXDViewModel;
    begin
      Application.Initialize;
      Application.CreateForm(TDataMod, DataMod);
      Application.CreateForm(TMainForm, MainForm);
      ViewModel := TEXDViewModel.Create;
      MainForm.Data := DataMod;
      MainForm.ViewModel := ViewModel;  //This throws an access violation exception
      ViewModel.Data := DataMod;
     Application.Run;
end.

我在VCL应用程序中做到这一点没有问题.我该如何解决?

I have no problem doing this in a VCL app. How do I fix it?

推荐答案

VCL和FMX之间的行为有所不同-FireMonkey Application.CreateForm方法.虽然在VCL CreateForm中实际上创建了表单，并且在调用之后将表单变量完全初始化并准备使用，但在FMX CreateForm中不会创建表单，并且在调用之后表单变量仍会被未初始化-nil.因此，使用form变量会抛出AV.

There is difference in behavior between VCL and FMX - FireMonkey Application.CreateForm method. While in VCL CreateForm actually creates form and after that call form variable is fully initialized and ready to be used, in FMX CreateForm does not create form and form variable would still be uninitialized - nil - after that call. Because of that using form variable throws AV.

FMX.TApplication.CreateForm

CreateForm不会立即创建给定的表单.它只是增加了一个 请求到待处理列表. RealCreateForms创建真实表单.

CreateForm does not create the given form immediately. It just adds a request to the pending list. RealCreateForms creates the real forms.

FMX具有Application.RealCreateForms方法，该方法在Application.Run中自动调用.如果在此之前需要使用表单变量，则可以自己调用Application.RealCreateForms.调用之后，您可以安全地使用通过Application.CreateForm

FMX has Application.RealCreateForms method that is automatically called in Application.Run. If you need to use form variables before that, you can call Application.RealCreateForms yourself. After that call you can safely use form variables you added to the list with Application.CreateForm

请记住，Application.RealCreateForms仅会进行一次表单创建过程，因此您必须在 向Application.CreateForm进行了所有调用之后将其称为最终会出现一些单位化的形式.

Keep in mind that Application.RealCreateForms will go through form creation process only once, so you have to call it after you made all calls to Application.CreateForm or you will end up with some unitialized forms.

begin
  Application.Initialize;
  Application.CreateForm(TDataMod, DataMod);
  Application.CreateForm(TMainForm, MainForm);

  // this forces creation of FireMonkey forms
  Application.RealCreateForms;
  ....

---

注意:在Windows和OSX平台上，RealCreateForms是在Application.Run中首先调用的，因此无论您是自动调用还是自动调用都无关紧要.但是，在Android和iOS平台上，在Application.Run中调用RealCreateForms之前会发生其他(初始化)逻辑，如果为这些平台开发，则在使用RealCreateForms时应谨慎行事，并注意潜在的副作用.对于移动平台，最好的选择可能是将您的自定义初始化移到Form OnCreate事件中.

---

Note: On Windows and OSX platforms RealCreateForms is first thing that is called in Application.Run, so it does not matter whether it is called by you or automatically. However, on Android and iOS platforms additional (initialization) logic happens before RealCreateForms is called in Application.Run, if you develop for those platforms, you should proceed with caution when using RealCreateForms and watch for potential side-effects. Probably the best option for mobile platforms would be to move your custom initialization into Form OnCreate event.

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