Handler callback function stops working, why?

[Numba1stunna]

Can someone explain to me why this doesn't work? Do hidden frames not execute "OnUpdate" script handler? I am confused. This is an extremely simple UI addon which shows an icon on target/focus if they're in combat or not in combat. I localized each function for each handler, but it seems that once the frame is hidden, it can't execute the callback anymore. Why?

--combat script
local UnitAffectingCombat = UnitAffectingCombat;
 
local TargetCombatFrame=CreateFrame("Frame")
TargetCombatFrame:SetParent(TargetFrame)
TargetCombatFrame:SetPoint("LEFT",TargetFrame,"RIGHT",0,0)
TargetCombatFrame:SetSize(35,35)
TargetCombatFrame.t=TargetCombatFrame:CreateTexture(nil,BORDER)
TargetCombatFrame.t:SetAllPoints()
TargetCombatFrame.t:SetTexture("Interface\\Icons\\Ability_Sap")
TargetCombatFrame:Show()
 
local function FrameOnUpdate(self,elapsed)
    print("test1")
    if not UnitAffectingCombat("target") then 
        self:Show() 
    else 
        self:Hide() 
    end 
end 
TargetCombatFrame:SetScript("OnUpdate",FrameOnUpdate)
 
local FocusCombatFrame=CreateFrame("Frame")
FocusCombatFrame:SetParent(FocusFrame)
FocusCombatFrame:SetPoint("RIGHT",FocusFrame,"LEFT",0,0)
FocusCombatFrame:SetSize(35,35)
FocusCombatFrame.t=FocusCombatFrame:CreateTexture(nil,BORDER)
FocusCombatFrame.t:SetAllPoints()
FocusCombatFrame.t:SetTexture("Interface\\Icons\\Ability_Sap")
FocusCombatFrame:Show()
 
local function FrameOnUpdate(self,elapsed)
    print("test2")
    if not UnitAffectingCombat("focus") then 
        self:Show() 
    else 
        self:Hide() 
    end 
end 
FocusCombatFrame:SetScript("OnUpdate",FrameOnUpdate)

[Fizzlemizz]

Hiding a frame stops the OnUpdate process until the frame is shown again. You could make it fully transparent.

[SDPhantom]

Here's what I came up with as well as improving the code.

local UnitAffectingCombat=UnitAffectingCombat;
local SecureButton_GetUnit=SecureButton_GetUnit;
 
local Textures={};--    Texture object lookup table
local function OnUpdate(self) Textures[self]:SetShown(UnitAffectingCombat(SecureButton_GetUnit(self))); end
 
local function SetupCombatTexture(frame,...)--  Passes vararg to :SetPoint()
    if not Textures[frame] then
        local tex=frame:CreateTexture(nil,"BORDER");
        tex:SetPoint(...);--    Set point from vararg
        tex:SetSize(35,35);
        tex:SetTexture("Interface\\Icons\\Ability_Sap");
 
        Textures[frame]=tex;--  Store texture in our lookup table
        frame:HookScript("OnUpdate",OnUpdate);--    Register our hook
    end
end
 
SetupCombatTexture(TargetFrame,"LEFT",TargetFrame,"RIGHT");
SetupCombatTexture(FocusFrame,"RIGHT",FocusFrame,"LEFT");

This simply creates textures on the existing frame you were attaching them to instead of making dynamic frames for that purpose. Since you can hook frame scripts using :SetHook(), there really isn't a need for extra frames for script handling. This also uses the fact that TargetFrame and FocusFrame inherit SecureUnitButtonTemplate, which allow using SecureButton_GetUnit() to get their set unit instead of hard-coding them. This will allow you to reuse the code for other frames that inherit the same template.

[Numba1stunna]

Nice use of SecureButton_GetUnit, I didn't even know that existed. There's probably more API I don't know about.