通过 Tag 属性查找 TImage

Question

I am using C++Builder and I have 64 TImage controls with different Tag values. Can I find an Image by its Tag somehow? I need this because my function has to move between two objects (which are Images) by adding 1 to their Tag s. I am using the VCL library.

Answer 1

There is no function available in the VCL to do this for you. You will have to manually loop through the Components[] property of the owning TForm , or the Controls[] property of the Parent of the TImage controls, checking each component/control for TImage before accessing their Tag , eg:

TImage* TMyForm::FindImageByTag(NativeInt ATag)
{
    for(int i = 0; i < ComponentCount /* or: SomeParent->ControlCount */; ++i)
    {
        if (TImage *img = dynamic_cast<TImage*>(Components[i] /* or: SomeParent->Controls[i] */))
        {
            if (img->Tag == ATag)
                return img;
        }
    }
    return NULL;
}

TImage *img = FindImageByTag(...);
if (img)
    img->Tag = img->Tag + 1;

Alternatively, you should store pointers to your TImage controls in your own array, which you can then index into/loop through when needed, eg:

private:
    TImage* Images[64];

...

__fastcall TMyForm::TMyForm(TComponent *Owner)
    : TForm(Owner)
{
    Images[0] = Image1;
    Images[1] = Image2;
    Images[2] = Image3;
    ...
    Images[63] = Image64;
}

TImage* TMyForm::FindImageByTag(NativeInt ATag)
{
    for(int i = 0; i < 64; ++i)
    {
        if (Images[i]->Tag == ATag)
            return Images[i];
    }
    return NULL;
}

When populating the array, if you don't want to hard-code the 64 pointers individually, you can use a loop instead:

__fastcall TMyForm::TMyForm(TComponent *Owner)
    : TForm(Owner)
{
    int idx = 0;
    for(int i = 0; (i < ComponentCount /* or: SomeParent->ControlCount */) && (idx < 64); ++i)
    {
        TImage *img = dynamic_cast<TImage*>(Components[i] /* or: SomeParent->Controls[i] */)
        if (img)
            Images[idx++] = img;
    }
}

Alternatively, using the Form's FindComponent() method:

__fastcall TMyForm::TMyForm(TComponent *Owner)
    : TForm(Owner)
{
    int idx = 0;
    for(int i = 1; i <= 64; ++i)
    {
        TImage *img = dynamic_cast<TImage*>(FindComponent(_D("Image")+String(i)));
        if (img)
            Images[idx++] = img;
    }
}