Check if an index exists on a table
I have a problem; I have to check in my program one field in a table.
if(launchArgs.androidIntent.extras.notification.custom.test_field ~= nil)then...
and when this index exists, everything is fine, but when it does not exist I get the error:
Attempt to index field 'notification' (a nil value).
And this is understandable. How can I check if this index exists?
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3 answers
try it
if (launchArgs and launchArgs.androidIntent and launchArgs.androidIntent.extras
and launchArgs.androidIntent.extras.notification and launchArgs.androidIntent.extras.notification.custom
and launchArgs.androidIntent.extras.notification.custom.test_field) then
-- do you stuff
end
This code checks if each table is installed.
If you are sure that the launch args.androidIntent.extras is always set, you can simply do this
if(launchArgs.androidIntent.extras.notification and launchArgs.androidIntent.extras.notification.custom and launchArgs.androidIntent.extras.notification.custom.test_field)then
-- do your stuff
end
OR Just use this function which I posted in another answer (helps here too)
function IndexScan(input,value,case,_type)
if (input and type(input) == 'table') then
if (_type) then
if (type(value) == _type and value == input) then
return true;
end
else
if (type(value) == 'table' and value == input) then
return true;
end
end
for key,object in pairs(input) do
if (case and type(input)=='string' and type(key)=='string') then
if (_type) then
if (value:lower() == key:lower() and type(object)==_type) then
return true;
elseif(type(object)=='table') then
return IndexScan(object,value,case,_type)
end
else
if (value:lower() == key:lower()) then
return true;
elseif(type(object)=='table') then
return IndexScan(object,value,case,_type)
end
end
else
if (_type) then
if (key == value and type(object)==_type) then
return true
elseif(type(object)=='table') then
return IndexScan(object,value,case,_type)
end
else
if (key == value) then
return true
elseif(type(object)=='table') then
return IndexScan(object,value,case,_type)
end
end
end
end
end
return false;
end
-- IndexScan(@param table(table), @param index(string), @param case-sensitive(true/false), @param type (index type, string/boolean/number/table ...))
-- checks if these two indexes were set any where in the launchArgs table and checks their type
if (IndexScan(launchArgs,"notification",false,"table") and IndexScan(launchArgs,"test_field",false,"string")) then
-- do your stuff
end
EDIT: Fixed some bug in the function.
EDIT: Updated script after the author fixed the Notification typo.
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Try also:
function setglobal(name,value)
local t=_ENV
local f="_G"
for x in name:gmatch("[^.]+") do
if t[f]==nil then t[f]={} end
t=t[f]
f=x
end
t[f]=value
end
function getglobal(name)
local t=_ENV
for x in name:gmatch("[^.]+") do
t=t[x]
if t==nil then return nil,x end
end
return t
end
setglobal("launchArgs.androidIntent.extras.notification.custom.test_field",2014)
print(getglobal("launchArgs.androidIntent.extras.notification.custom.test_field"))
print(getglobal("launchArgs.androidIntent.extras.notifiaction.custom.test_field"))
This assumes that the top-level variable is a global variable. Adapt if necessary.
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You can use this:
local function try(root, query)
local ids, len = {}, 0
for id in query:gmatch("%w+") do
len = len + 1
ids[len]= id
end
local node = root
for i=1,len do
if type(node) ~= 'table' then return nil end
node = node[ids[i]]
end
return node
end
Using:
local tbl = { a = { b = { c = { d = 1 } } } }
print(try(tbl, 'a.b.c.d')) -- prints 1
print(try(tbl, 'a.b.c.x')) -- prints nil
print(try(tbl, 'a.x.c.d')) -- prints nil
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