Wish Missing Function MAP

[mcGeorge]

Hi, i often use the methods

"Map.GetKeyAt()" and "Map.GetValueAt()"

in my B4A-Programms.

Is it possible to implement these methods in B4I?

Thanks, George

 

[billzhan]

+1

 

[Erel]

These methods will not be added.

The only purpose of these methods in B4A was to allow developers to iterate over the Map items. This was before the For Each loop was available.
A standard Map structure doesn't support these methods so adding them requires a more complicated (and less optimized) structure.

For Each k As String In Map.Keys
 Dim v As Object = Map.Get(k)
 ...
Next

This code is faster and doesn't require a custom structure under the hood.

 

[jcesar]

But if i need recover a key for some value ?

 

[LucaMs]

The only purpose of these methods in B4A was to allow developers to iterate over the Map items

Ok, but please, do not remove them from B4A

 

[Erel]

Ok, but please, do not remove them from B4A

They will not be removed.

But if i need recover a key for some value ?

Hash maps are not suitable for this task. It is better to use two maps in this case.

This task requires linear search:

Sub FindKeyForValue(m As Map, v As Object) As Object
 For Each k As Object in m.Keys
   If m.Get(k) = v Then Return k
 Next
End Sub

 

[tamayo461]

Hi, i often use the methods

"Map.GetKeyAt()" and "Map.GetValueAt()"

in my B4A-Programms.

Is it possible to implement these methods in B4I?

Thanks, George

You managed to implement the method in iOs?

 

[Erel]

These methods are not available in B4i. You should instead use For Each to iterate over the items.

 

[JonPM]

These methods will not be added.

The only purpose of these methods in B4A was to allow developers to iterate over the Map items. This was before the For Each loop was available.
A standard Map structure doesn't support these methods so adding them requires a more complicated (and less optimized) structure.

For Each k As String In Map.Keys
Dim v As Object = Map.Get(k)
...
Next

This code is faster and doesn't require a custom structure under the hood.

The reasoning is logical, however there is one profound reason why you should implement these methods: to maintain the promise of a cross-platform suite. Migrating large projects from B4A to B4i is mostly unobtrusive, however these sort of inconsistencies slow the process.

 

[Erel]

It is not possible to add these methods without a building a completely new collection (with worse performance, more overhead and less flexibility). As these methods are deprecated and there is a better alternative I decided that they will not be implemented.

 

[Bryanne Vega]

I worked around this issue in the TableView by passing my data to each cell's tag.

Sadly I cant either port directly non UI code because of this.

 

[iCAB]

Can I trust, the loop below to return the keys in the same order as if I used I used B4A, "Map.GetKeyAt(i)" and "Map.GetValueAt(i)" .

For Each k As String In Map.Keys
Dim v As Object = Map.Get(k)
...
Next

In other words

Dim iLoopIndex As Int = 0
Dim iKeyIndex As Int = 5

For Each k As String In mLocalMap.Keys
     Dim v As Object = mLocalMap.Get(k)
     ...
     If iLoopIndex = iKeyIndex Then
         Exit
    End If
     iLoopIndex = iLoopIndex + 1
Next

Is k = GetKeyAt(5) ??? assuming that map size is > 6

 

[Erel]

No. The order is not preserved.