使用Corona SDK从Google Distance Matrix API解析JSON

Question

So I'm trying to pull data from a JSON string (as seen below). When I decode the JSON using the code below, and then attempt to index the duration text , I get a nil return. I have tried everything and nothing seems to work.

Here is the Google Distance Matrix API JSON :

{
    "destination_addresses" : [ "San Francisco, CA, USA" ],
    "origin_addresses" : [ "Seattle, WA, USA" ],
    "rows" : [
    {
        "elements" : [
        {
            "distance" : {
                "text" : "1,299 km",
                "value" : 1299026
            },
            "duration" : {
                "text" : "12 hours 18 mins",
                "value" : 44303
            },
            "status" : "OK"
        }]
    }],
    "status" : "OK"
}

And here is my code:

local json = require ("json")
local http = require("socket.http")
local myNewData1 = {}
local SaveData1 = function (event)

distanceReturn = ""
distance = ""

local URL1 = "http://maps.googleapis.com/maps/api/distancematrix/json?origins=Seattle&destinations=San+Francisco&mode=driving&&sensor=false"
local response1 = http.request(URL1)
local data2 = json.decode(response1)

if response1 == nil then
    native.showAlert( "Data is nill", { "OK"})
    print("Error1")
    distanceReturn = "Error1"

elseif data2 == nill then
    distanceReturn = "Error2"
    native.showAlert( "Data is nill", { "OK"})
    print("Error2")         
else
    for i = 1, #data2 do
        print("Working")  
        print(data2[i].rows)

        for j = 1, #data2[i].rows, 1 do
            print("\t" .. data2[i].rows[j])

            for k = 1, #data2[i].rows[k].elements, 1 do
                print("\t" .. data2[i].rows[j].elements[k])

                for g = 1, #data2[i].rows[k].elements[k].duration, 1 do                         
                    print("\t" .. data2[i].rows[k].elements[k].duration[g])

                    for f = 1, #data2[i].rows[k].elements[k].duration[g].text, 1 do
                        print("\t" .. data2[i].rows[k].elements[k].duration[g].text)

                        distance = data2[i].rows[k].elements[k].duration[g].text
                        distanceReturn = data2[i].rows[k].elements[k].duration[g].text

                    end
                end
            end 
        end 
    end
end

timer.performWithDelay (100, SaveData1, 999999)

Answer 1

Your loops are not correct. Try this shorter solution.

Replace all your "for i = 1, #data2 do" loop for this one below:

print("Working")  

for i,row in ipairs(data2.rows) do
    for j,element in ipairs(row.elements) do
        print(element.duration.text)
    end
end

Answer 2

This question was solved on Corona Forums by Rob Miracle ( http://forums.coronalabs.com/topic/47319-parsing-json-from-google-distance-matrix-api/?hl=print_r#entry244400 ). The solution is simple:

"JSON and Lua tables are almost identical data structures. In this case your table data2 has top level entries:

data2.destination_addresses
data2.origin_addresses
data2.rows
data2.status

Now data2.rows is another table that is indexed by numbers (the [] brackets) but here is only one of them, but its still an array entry:

data.rows[1]

Then inside of it is another numerically indexed table called elements. So far to get to the element they are (again there is only one of them

data2.rows[1].elements[1]

then it's just accessing the remaining elements:

data2.rows[1].elements[1].distance.text
data2.rows[1].elements[1].distance.value
data2.rows[1].elements[1].duration.text
data2.rows[1].elements[1].duration.value

There is a great table printing function called print_r which can be found in the community code which is great for dumping tables like this to see their structure."