尝试索引升值 'letter' 的错误，因为 arr_str[i]。

我正尝试为我的游戏创建一个随机字母答案，但问题是它无法检测到图像，请帮忙...

local s = answer --答案
local len = string.len(answer)
local str
local j

for j=1,len do
    str = s:sub(j,j)
    arr_str[j]= str
end

    for i = 1, #arr_str do
        local j = math.random( 1,#arr_str)
        arr_str[i], arr_str[j] = arr_str[j], arr_str[i]
    end

local max = #arr_str
local rowMax = max
--如果max>8 rowMax = 8 结束
local gap = 35
local xPos = halfW - (rowMax/2*35) + 17.5
local yPos = bottom - 20
local startpos = xPos

for i= 1, #arr_str do

    slot = display.newImageRect( "images/bg_slot.png", 43, 43 )
    slot.x = xPos; slot.y = yPos -40
    slotgroup:insert( slot )

    slot1 = display.newImageRect( "images/ans_slot.png", 43, 43 )
    slot1.x = xPos; slot1.y = yPos
    slotgroup:insert( slot1)

    print("ERROR",arr_str[i])
    letter = display.newImageRect("letters/uc/".. arr_str[i] ..".png",50,50)
    letter.name = arr_str[i]
    letter.x = xPos; letter.y = yPos
    letter.idBg = i
    lettergroup:insert( letter)

    xPos = xPos + gap