当两个地图都仍打开时，如何使用B4A中的两个地图对象更新一个地图文件？

Question

how to update one map file using two Map objects in B4A when both Maps are still open?
My code is :

dim MapForUser1, MapForUser2 as Map<br>
MapForUser1 = File.ReadMap(File.DirInternal, "scores.dat")
MapForUser2 = File.ReadMap(File.DirInternal, "scores.dat")

One user updates some key value of 113:

Dim s1 as String
s1 = MapForUser1.Get("113")  

here update s1 then delete the key and add new item with same key

MapForUser1.Remove("113")  
MapForUser1.Put("113", s1)  

File.WriteMap(File.DirInternal, "scores.dat", MapForUser1)

it works very good in all situations
If second user updates value of same key 113:

Dim s2 as String
s2 = MapForUser2.Get("113")

here update s2 then delete the key and add new item with same key

MapForUser2.Remove("113")
MapForUser2.Put("113", s2)
File.WriteMap(File.DirInternal, "scores.dat", MapForUser2)

it works very good in all situations
It shows everything good but second user's update is added as a new Item rather than updating the existing item with key 113

Both users use same Activity of an App at the same time. how to manage the second user's update properly when first has already opened the map for a file. Second user is unable to delete the item for the same key that first user updated first but didn't close the activity. If first user closes the activity and then second user updates same item, then it is working. But adding a duplicate key is too horrible to think about in mapping. due to duplicate key the whole game is crashing many times. Please help with some working code example.

Thank you
Rupali

Answer 1

MapForUser1 and MapForUser2 are two different Maps so their respective "113" keys are two different data sets already but if having the same key name simplifies your code then you should use two data files, one for each user to allow for independent update. File.WriteMap() writes in a sequential text file. Without seeing more of your code it is very likely that handling file read/write operations and synchronizing it with two users causes the problem.

If you insist on using one data file it is better to use Random Access File.

RandomAccesFile.WriteObject(Object,Compress as Boolean,Position as Byte)

    Dim raf As RandomAccessFile
raf.initialize(File.DirRootExternal,"score.dat",False)

raf.WriteObject(MapForUser1,True,0)     'write from byte'
raf.WriteObject(MapForUser2,True,5000)  'write from byte 5000' 

raf.Close

Then to read:

raf.initialize(File.DirRootExternal,"score.dat",False)


MapForUser1=raf.ReadObject(0)         'read from byte 0'
MapForUser2=raf.ReadObject(5000)       'read from byte 5000'

raf.Close

Take a look here: https://b4x.com/android/forum/threads/write-2-map-views-to-a-single-txt-file.48974/