Android Question Retrieving Type Data From File.ReadMap Gives Imcompatible Types Error

Mahares · Mar 17, 2020

When I extract the map data from the saved map file as shown below, I get the error on line 62 as shown below: But if I put the Type members data in a map before saving it , it works well. How would you read the data from the saved map and make it display the 'Type' members. Thank you

B4X:

Type StudentType(id As Int, name As String, myclass As String, section As String)

B4X:

Sub DisplayData
    Dim MyMap As Map
    MyMap.Initialize
    MyMap=File.Readmap(File.DirInternal, "maptrivia")    
    For Each s As StudentType In MyMap    'line 62  error
        s = MyMap.GetValueAt(0)
        Log($"${s.id} ${s.name}  ${s.myclass}  ${s.section}"$)  
    Next
End Sub

B4X:

B4A line: 62
For Each s As StudentType In MyMap
src\b4a\example\main.java:491: error: incompatible types: Map cannot be converted to IterableList
final anywheresoftware.b4a.BA.IterableList group4 = _mymap;

drgottjr · Mar 17, 2020

as the error says, map is not iterable. step through your map:

B4X:

For i = 0 to Map.Size - 1
 '   Log("Key: " & Map.GetKeyAt(i))
  '  Log("Value: " & Map.GetValueAt(i))
   dim s as studenttype = map.getValueat(i)
Next

Mahares · Mar 17, 2020

drgottjr said:
as the error says, map is not iterable. step through your map:

I stepped thru it and got similar results. I think it has to do with the data extracted as a string when read from a saved map file. Can you try it and let us know.

Erel · Mar 17, 2020

There are several other mistakes that you should avoid:

B4X:

 Dim MyMap As Map
    MyMap.Initialize
    MyMap=File.Readmap(File.DirInternal, "maptrivia")

Don't initialize the object if you are assigning a different object to the same variable.
Correct:

B4X:

Dim MyMap As Map = File.ReadMap(...)

Never use GetValueAt or GetKeyAt.
Iterating over a map:

B4X:

For Each Key As Object In MyMap.Keys 'change Object to correct type if type is known
  Dim Value As StudentType = MyMap.Get(Key)
Next
'you can also iterate over the values:
[code]
For Each Student As StudentType In MyMap.Values

Next

As you wrote, File.WriteMap / ReadMap is only good for simple values as it creates a text file. You should either use B4XSerializator and save the data with File.WriteBytes or just choose the best option which is to use KeyValueStore2.

DonManfred · Mar 17, 2020

Mahares said:
MyMap=File.Readmap(File.DirInternal, "maptrivia")

File. ReadMap (Dir As String, FileName As String) As Map
Reads the file and parses each line as a key-value pair (of strings).

You should use b4xserialisator to store and read a list with customtypes

Edit: too late ;-)

Mahares · Mar 17, 2020

Erel said:
terating over a map:

I tied both variances and neither worked:

B4X:

Sub DisplayData
    Dim MyMap As Map
    MyMap=File.Readmap(File.DirInternal, "maptrivia")
    For Each Key As Int In MyMap.Keys 'change Object to correct type if type is known
       Dim s As StudentType = MyMap.Get(Key)    'error
       Log($"${s.id} ${s.name}  ${s.myclass}  ${s.section}"$)  
    Next
    'java.lang.NullPointerException: Attempt to invoke virtual method 'boolean java.lang.String.equals(java.lang.Object)' on a null object reference
End Sub

B4X:

Sub DisplayData
    Dim MyMap As Map
    MyMap=File.Readmap(File.DirInternal, "maptrivia")      
    For Each s As StudentType In MyMap.Values
        Log($"${s.id} ${s.name}  ${s.myclass}  ${s.section}"$)  'error
    Next
'    java.lang.RuntimeException: Field: id not found in: java.lang.String
End Sub

Erel · Mar 17, 2020

That's expected. As I wrote:
File.WriteMap / ReadMap is only good for simple values as it creates a text file.

Mahares · Mar 17, 2020

Erel said:
That's expected. As I wrote:

That is what I wrote in my previous post too about strings , I am aware of that, but after you offered some sample codes, I thought they would work, so I tried.

DonManfred · Mar 17, 2020

Mahares said:
I tied both variances and neither worked

it will not work with File.ReadMap. You never get a MAP here.

Mahares · Mar 17, 2020

DonManfred said:
You should use b4xserialisator to store and read a list with customtypes

DonManfred said:
it will not work with File.ReadMap. You never get a MAP here.

I am not familiar with b4xserialisator. If it is hard reading and one more thing to learn, I will avoid maps and resort to my safety net which is always: SQLite that works for me in such similar circumstances.

DonManfred · Mar 17, 2020

Mahares said:
I am not familiar with b4xserialisator

Make your live more easy. Use KVS2.

Store the map to a key of your needs.
Read back the map from KVS2 using the Key used. Iterate through your Map

Or maybe better to use a List of customTypes and store the list.
It depends on your needs. Map, List, both are possible in KVS2. Even combined ones.

Android Question Retrieving Type Data From File.ReadMap Gives Imcompatible Types Error

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