检查表中的索引是否存在

Question

我有问题; 我必须在表格中查看我的程序中的一个字段.

if(launchArgs.androidIntent.extras.notification.custom.test_field ~= nil)then...

当这个索引存在时一切正常,但是当它不存在时,我收到一个错误:

Attempt to index field 'notification' (a nil value).

这是可以理解的.如何检查该索引是否存在？

Answer 1

试试这个

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

此代码将检查是否已设置每个表.

如果你确定启动args.androidIntent.extras总是设置你可以这样做

if(launchArgs.androidIntent.extras.notification and launchArgs.androidIntent.extras.notification.custom and launchArgs.androidIntent.extras.notification.custom.test_field)then
    -- do your stuff
end

或者只是使用这个函数,我在其他答案中发布(在这里也有帮助)

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

编辑: 修复了函数中的一些错误.

编辑: 在作者修复了通知错误后更新了脚本.