I have been plagued with this error for several months. Sometimes it occurs and sometimes it does not.
I have several TComboBoxes or TComboEdits in my application.
I am doing nothing more that populate the control with a SQLite query via an array of string values.
I have coded no change events. Just touching the control brings up the iOS native control which has the list contents. However, sometimes touching the control causes the "External Exception 0" error. This is maddening.
Anyone else encounter this error?
I encountered external exception 0 in android. How I got the problem and what changes I did to get rid of it I will tell.
I was invoking a third form from a second form (by lazy creation and showing). The third form displayed fine but when I tried to access any control in the parent form through the second form's unit (included in the implementation uses section of third form) like uSecond.Form2.myControl I got that exception (note: Form2 is the global var in uSecond).
How I solved the issue was I put the mainForm's unit besides the uSecond in the implementation uses of the third form and ensured that units of both form2, form3 were present in the mainForm's implementation uses section. Then I referenced in my third form - the global var defined for the same second form but in the mainForm (not in uSecond) like uMain.FormTwo.myControl
Note that Form2 and FormTwo are two different identifiers.
Related
I've had this long time problem that I can't view as text the main form for a project I inherited. Even if no other forms are open.
How can I debug the cause of this error message? What options do I have to fix it?
I found one related newsgroup post http://embarcadero.newsgroups.archived.at/public.delphi.ide/200906/0906193960.html but this only addresses the form inheritance cause, and doesn't explain anything about linked modules. I don't believe I'm using form inheritance.
I do have a DM (data module) for the project, and the form does load a couple of images from the dm through properties of a TTreeView on the form--does having a data module automatically mean I can never view as text a form in Delphi (aside from viewing the form as text in notepad)? It doesn't seem to matter whether my DM is open or closed in the IDE.
I also found one SO question with a related title (Module %s has open descendants or linked modules. can not reload) but the question itself and it's answer is not particularly relevant.
This is sometimes caused by a form that inherits from another form in your project (or the gallery) (known as Visual Form Inheritance in the documentation, IIRC). The IDE doesn't know how to find the base class for the form; it needs that opened before the descendant form. For instance, this can cause the same error if the unit containing TMyBaseForm isn't opened first in the IDE, particularly if the base (ancestor) unit is not included in the project first:
unit SpecialForm;
interface
uses
Forms, { all the other usual stuff }, BaseForm;
type
TMySpecialForm = class(TMyBaseForm)
private
public
end;
You can tell if this is the case by looking at your form's class declaration - if it descends from anything other than TForm, this is probably the cause of the error.
(Another instance of it happening is often when using a datamodule, because the base TDataModule .DFM isn't available. Attempting to view the datamodule .DFM as text will cause this error every time; the solution is to close your project and use an external editor such as Notepad or Notepad++ to edit the .dfm for your datamodule.)
I've had this issue occasionally, perhaps when I've used Frames, but my latest instance didn't involve Frames nor Data Modules nor inherited forms.
After an enormous amount of work creating a copy of the form (which copy didn't have the problem) and renaming the original unit and the form itself (which initially seemed to solve the problem), it turned out to be a live binding between forms.
Specifically, in my FMX application Form A has an options page with a TSpinBox that allows the user to set the minimum value for a TTrackBar on Form B (which was the form giving me grief). So the TSpinBox.Value was set to update the TTrackBar.Min field by means of a live binding. Closing Form A, or removing that live binding (and replacing it with an event handler to do the same thing) solved the problem.
I'd like to call upon the answer of Phillip J. Rayment and ADD that you don't have to have live binding to have this problem occur. It's sufficient to have custom control (class) of which you have an instance in another form. Then the RLink32 problem can appear and won't be solved until you close the form where you have the instance. The problem I experienced gave the following messages:
-RLink32 (during building)
-Access violation in module designide160.bpl` (if I made a modification to the problematic form)
-The module has open descendants or linked modules” error (if I tried to 'View as Form')
I need to integrate drag&drop of our existing application with a new component.
Our application uses Winapi.ActiveX do implement this. The new component comes with its own drag&drop events which aren't Winapi-compatible, though.
The main problem for now is dragging things into the new control. Dragging out of it should be achievable, if all else fails by caching the object under the cursor on mouse down.
As I understand it you can't override drag&drop registration, that is if I call RegisterDragDrop on the component before they do it somewhere in their code, I'll be the one holding the registration.
The observed behavior, however, is that calling RegisterDragDrop reports success, but dragging something over the control doesn't lead to a DragEnter event on the IDropTarget. Their drag&drop event fires just fine, even after RegisterDragDrop, but as I said, the returned data object only holds valid data for a select few types of draggable objects.
I also tried registering the panel that contains this component for drag&drop, but that didn't work either.
What would you suggest?
Update:
I realized, I was trying to register the wrong handle. When I try to register the right handle, I actually get a drag&drop already registered error.
I guess I didn't formulate it too clearly, but the question is, how do you implement drag&drop for a closed-source component that already has it's own implementation, which doesn't provide enough flexibility for your taste?
What I can think of:
Bug the developer of the component until they change the component.
Do some API hooking to go in between the component's implementation and the OS.
Hopefully something else that is simple.
Update:
Thanks so far, now I can drag things into the control the way I want it.
The next step is dragging things out. Here the problem is that other drop targets in the application don't understand the control's IDataObject. For a different control we already have code that uses IDataObject::SetData to append data in a format that all the application's drop targets can understand.
The difference with the new control, however is that when it initiates a drag&drop operation, it doesn't use a IDataObject that has IDataObject::SetData implemented (returns E_NOTIMPL); Is there a way to replace the IDataObject with a different one, while the d&d operation is ongoing?
Try to reset already registered IDropTarget of your ActiveX control after control creation with the following code:
const
sOleDropTargetInterface = 'OleDropTargetInterface';
procedure ResetDropTarget(AWnd: HWND);
var
Unknown: IUnknown;
begin
Unknown := IUnknown(GetProp(AWnd, PChar(GlobalFindAtom(sOleDropTargetInterface))));
if Assigned(Unknown) then
try
if not SetProp(AWnd, PChar(GlobalFindAtom(sOleDropTargetInterface)), 0) then
RaiseLastOSError;
Unknown._Release;
finally
Unknown := nil;
end;
end;
Update
kobik points the right solution: using of RevokeDragDrop function.
I wrote a set of components that link to each other via published interface properties. They are registered and installed in a design package.
Using published interface properties is not that common in Delphi, and thus, unsurprisingly, doesn't seem to work that well.
It works fine when components reside on the same form, however interface property links between components on different forms cause issues.
Unlike object links to components on another form, interface links don't seem to be recognized by IDE. What I mean is best described by an example, when you have 2 forms open in IDE, and have links between components on them, then trying to switch to form view as text (Alt+F12) would cause IDE to correctly complain that:
Module 'UnitXXX.pas' has open descendents or linked modules. Cannot close.
But if the property is an interface then this does not happen, what happens instead is that the link is severed (and that's the best case scenario when you use Notification mechanism to clear references, otherwise you're left with an invalid pointer)
Another problem, likely as a consequence of the same bug is that when you open a project in IDE, the order in which forms will be reopened is undefined, so IDE can try to open a form that contains components that have interface links to components on another form, but that other form is not recreated yet. So this effectively results in either AV or severed links.
Back in 90s while I used Datasets and Datasources I remember similar issues with links between forms disappearing, so this is somewhat similar.
As a temp workaround I added duplicate published properties, for each Interface property I added another that is declared as TComponent. This makes Delphi aware there is a link between forms, but is an ugly workaround to say the least.
So I wonder if there is something I can do to fix this issue ? It's an IDE bug and likely not fixable directly, but perhaps I can override something or otherwise hook in to streaming mechanism to more effectively workaround this bug.
I haven't ever gone so deep into streaming mechanism, but I suspect the Fixup mechanism is supposed to deal with this. There is a csFixups TComponentState so I hope a workaround is possible.
Edit: Using D2007.
Update:
New updated reproducible example uploaded to http://www.filedropper.com/fixupbugproject2
Added property ComponentReference: TComponent so that it's easy to compare and trace interface vs component streaming.
I narrowed the problem down to assembler level which is a bit out of my depth.
In procedure GlobalFixupReferences in classes unit it calls:
(GetOrdProp(FInstance, FPropInfo) <> 0)
which eventually executes:
function TInterfacedComponent.GetInterfaceReference: IInterface;
begin
// uncomment the code bellow to avoid exception
{ if (csLoading in ComponentState) and (FInterfaceReference = nil) then
// leave result unassigned to avoid exception
else
}
result := FInterfaceReference; // <----- Exception happens here
end;
As you can see from the comment, the only way I found to avoid the exception is to leave the result unassigned, but that breaks the functionality since comparison above in GlobalFixupReferences fails due to GetOrdProp <> 0, which severes the link.
tracing deeper the more exact location of exception is in
procedure _IntfCopy(var Dest: IInterface; const Source: IInterface); in system unit
This line in particular raises an read of address 0x80000000
{ Now we're into the less common cases. }
##NilSource:
MOV ECX, [EAX] // get current value
So, why MOV fails and what's wrong with ECX or EAX I have no idea.
To summarize, the problem happens only with published interface properties that have a getter method, and the property points to component on another form/module (and that form/module is not recreated yet). In such case restoring form DFM causes an AV.
I'm pretty sure the bug is in the ASM code in GetOrdProp, but it's beyond my ability to fix, so the
easiest workaround is to use a Field instead of a getter method and read it directly in the property. This is, fortunately good enough for my case currently.
Alternatively, you can declare the property as TComponent instead of interface, then write a TComponentProperty descendant, override ComponentMayBeSetTo to filter component that don't support the required interface. And of course register it using RegisterPropertyEditor
I have a runtime error happening in the rtl Streaming in of a form, causing an exception EClassNotFound to be raised, while doing TReader.ReadRootComponent. The particular error message is "Class not found TActionList".
What is odd is:
My main form uses Action list.
For fun, I added ActnList.pas (from the VCL source folder) to my project, to try to fix it.
This happens to me when instantiating a form that I had working until a few minutes ago. The change that I made was in some sub-frame code: I removed all its implementation section code with an ifdef marker, because I am mocking up some frames, for unit testing and prototypes.
I tried adding the action list class to the project, and I tried with and without various compiler and link options, and yet, I still get this exception. Obviously something weird is up. There must be another weird way to get this problem.
In fact, it seems there is something really weird going on. When this error is raised, I get the following call stack:
rtl.Classes.ClassNotFound('TActionList')
rtl.Classes.TReader.FindComponentClass(???)
rtl.Classes.FindExistingComponent
rtl.Classes.TReader.ReadComponent(nil) /// NIL!? WHAT!!!!!
rtl.Classes.TReader.ReadDataInner(???)
rtl.Classes.TReader.ReadData(???)
rtl.Classes.TComponent.ReadState(???)
vcl.Controls.TControl.ReadState(???)
vcl.Controls.TWinControl.ReadState($60B9CF0)
vcl.Forms.TCustomForm.ReadState(???)
rtl.Classes.TReader.ReadRootComponent($606EB90)
rtl.Classes.TStream.ReadComponent($606EB90)
rtl.Classes.InternalReadComponentRes(???,???,$606EB90)
rtl.Classes.InitComponent(TComplexFormContainingFrames)
It seems the nil is intentional, in TReader.ReadDataInner(Instance:TComponent):
while not EndOfList do ReadComponent(nil);
Update: I believe the answer to this question is to understand "serialization contexts" as Mason has mentioned. And, it's time to admit my own Stupidity: I removed the parent of the frame from the project, not realizing it was the parent of the frame. I worked around it being missing by stubbing the type declaration for TMyFrameParent as TMyFrameParent = class(TFrame), and this in turn lead to the condition in question. I am leaving the question here because I think it might be really handy in future to note when this exception occurs in arcane cases, and how to fix it. In particular, Mason has a really interesting bit of information about "serialization contexts" and how they apply to class-name-finding.
It means that the class wasn't found in the current deserialization context. Not all existing classes are registered for all loading. Each form class has RTTI containing references to the components it uses. To get this to work, make sure that your form (or frame, if this is a frame) declares at least one TActionList before the private tag:
TMyForm = class(TForm)
ActionList: TActionList;
OtherComponent: TSomeComponent;
private
//whatever
public
//whatever
end;
Use Classes.RegisterClass to register classes you want to use with the streaming system. Quote from the doc
Form classes and component classes that are referenced in a form declaration (instance variables) are automatically registered. Any other classes used by an application must be explicitly registered by calling RegisterClass if instances are to be saved. Once classes are registered, they can be loaded or saved by the component streaming system.
It seems that this happens when you copy a frame from one project to another project, and that frame inherits from something, and you fake the inheritance, but leave the "inherited" item descriptions in the frame dfm, items like this:
inherited ActionList: TActionList
Left = 520
Top = 576
end
This in turn results in the "current deserialization context" that Mason talked about, not containing the class. One fix is to change Inherited to object in all the above cases.
There is another way to get this error: put 'public' at the top of a form definition class. By default class members are 'published'. I accidentally added 'public' to the top of a form declaration and it produces multiple 'Class not found' exceptions at run-time.
I got a "EClassNotFound" error when I had a TLabel declaration present in my DFM file but there was no declaration for it in the corresponding PAS file. Somehow the form editor screwed up.
The error was not visible until I deleted all labels from my form except that particular "corrupted" one. It was difficult to hunt it down because that label was hidden under a panel.
One easy fix is to cut (ctrl+x) that label (once you find it) from the form and paste it back. This time the form editor will correctly insert a declaration for it in the PAS file.
There is yet another way to get this error: I have put 'private' at the top of a form definition class (because none of the elements were used outside the form).
So same like in previous answer (by Server Overflow): by default class members are 'published' and if you change visibility of a form declaration it produces multiple 'Class not found' exceptions at run-time.
It was only recently that I started receiving this error.
I am receiving a run time error that first says 'Invalid Property Value', I click continue and then receive another one saying "Error reading Image2.OnClick : Invalid Property Value".
I use Image2 to manoeuvre between different forms. I have tried deleting all components named "Image2" along with any code under the OnClick event, but still receive the error.
Any suggestions?
Somewhere in one of your .dfm files that contain the design time properties of your forms, you have an OnClick property that refers to a method that has either been removed, or is invalid in some other way.
Open the .dfm file for the offending form in a text edit, and look for Image2. You will then find the offending OnClick property setting and should be able to work out how best to resolve the problem.
It's probably related to your method's access level.
If your OnClick method is declared as either private or public, try changing its access level to Published or move it right below the form declaration line.