类型 TMessage 不是定义的 class 虚函数 C++ 生成器示例

Question

我正在尝试使用 embarcadero 示例来使用 android 相机并收到错误消息：

"type TMessage is not a defined class with virtual function" on lines:

void __fastcall TForm1::DoMessageListener(const TObject *Sender, TMessage const *M) {
    TMessageDidFinishTakingImageFromLibrary const *v = dynamic_cast<TMessageDidFinishTakingImageFromLibrary const *>(M);
    if (v) {
        Image1->Bitmap->Assign(v->Value);
    }
}

Answer 1

在Delphi中，TMessage works fine, but in C++Builder you must use TMessageBase改为：

void __fastcall TForm1::DoMessageListener(const TObject *Sender, TMessageBase const *M)

这在文档中有明确说明：

Sending and Receiving Messages Using the RTL:

The RTL only defines one type of message, TMessage. It is actually a template that you can use to create messages for specific types of values; for example: TMessage<int> or TMessage<UnicodeString>. You can also subclass TMessage to define your own message types or, if you are using FireMonkey, you can reuse the message types defined by the framework.

Note: For C++ projects use TMessageBase instead of TMessage.

System.Messaging.TMessage

TMessage represents the base class used for message purposes. It can be inherited in order to send custom messages.

Warning: For C++ projects, use TMessageBase instead.

System.Messaging.TMessageBase

Alias to System.Messaging.TMessage.

Use System.Messaging.TMessageBase for C++ projects instead of System.Messaging.TMessage.

文档的 System.Messaging (C++) 示例中也演示了 TMessageBase 的这种用法。

类型 TMessage 不是定义的 class 虚函数 C++ 生成器示例

type TMessage is not a defined class with virtual function C++ builder sample

c++builder