Android Question Right way to organize your database functions across separate code modules for sharing across B4xPages.

beelze69 said:

4) Now, in order to segregate all my Application specific Database Public functions, I tried to move them by creating a separate class and putting them there.

But I am unable to reference the Public Functions from my B4XPages

by <className>.dbFunction1() .

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LucaMs said:

Writing all public methods (the Subs) in a class is the right choice.
To use them, however, you must create an instance of the class, that is create a variable (public, for example gDB) of type clsDB (names of your choice, obviously) and initialize it. Where to do it? The best place is the B4XMainPage.

At that point in any other B4XPage you can write:
B4XPages.MainPage.gDB.SomeDBMethod(...)

In the class write also the methods to initialize and close the DB.

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beelze69 said:

Hi LucaMs,

Thanks...I will try it and revert back if any issues...

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Sub Process_Globals() Public SQL As SQL Public SafeDirectory As String Public RTP As RuntimePermissions Public DBName As String="myDatabaseName.db" End Sub

Sub Service_Create
SafeDirectory = RTP.GetSafeDirDefaultExternal("")
If File.Exists(SafeDirectory, DBName) = False Then
Wait For (File.CopyAsync(File.DirAssets, DBName, SafeDirectory, DBName)) Complete (Success As Boolean) 'File.DirInternal
'    ToastMessageShow($"DB Copied = ${Success}"$, False)
Log("Success: " & Success)
End If
 
ConnectToDatabase
    Wait For SQLite_Ready (Success As Boolean)
End Sub

Public Sub ConnectToDatabase
    SQL.Initialize( SafeDirectory, DBName, False)
End Sub

Sub Class_Globals
'**********Declarations for the clsGen ************
Public selectedParamValue As String
End Sub

Public Sub isMyConditionMet() As ResumableSub
    'Invoked for clsGen..
    'This function returns true if the SQL Condition is satisfied, false otherwise..
    Dim SenderFilter As Object
    Dim retValue As Boolean
    retValue=False
 
    SenderFilter=Starter.SQL.ExecQueryAsync( "SQL",<select count(fieldname) as countOfRecordsFound from tableName where fieldName=selectedParamValue>,Null)
    Wait For (SenderFilter) SQL_QueryComplete (Success As Boolean, RS As ResultSet)
    If Success Then
     
        RS.NextRow 'must be atleast 1 record
        If RS.GetInt("countOfRecordsFound")> 0 Then
         
            retValue=True
        Else
            retValue=False
        End If
     
        RS.Close
 
        Return(retValue)
    Else
        Log(LastException)
        Return(retValue)
    End If
End Sub

Sub Class_Globals
Private myClass As clsGen
End Sub

Public Sub Initialize
'    B4XPages.GetManager.LogEvents = True
myClass.Initialize
End Sub

Sub myCallingSubroutine()

    'Passing the parameter to the variable declared in the class file
        myClass.selectedParamValue="someValue"
     
     
        Dim  theFunction As ResumableSub=myClass.isMyConditionMet()
        Log("checking for the condition)
        Wait For(theFunction) Complete (myRetValue As Boolean)
        If myRetValue==True Then
            'The match is found
            Wait For (ShowToast("conditon matched",  2000,"Normal")) Complete(Unused As Boolean)

                Else
                    'The match is not found
        Wait For (ShowToast("Condition did not match...",  2000,"ERROR")) Complete(Unused As Boolean)
        End If
End Sub

'Note: ShowToast is my User-Defined-function that just displays a coloured message depending on the parameter string I pass to it viz. Normal or ERROR etc..

beelze69 said:

4.1) Whether I have declared and initialized my class module the right way in Point 3)

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beelze69 said:

4.2) Is there a better way to pass the parameter in Point 3 ) than the present way of

myClass.selectedParamValue="someValue"

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Public Sub isMyContiditionMet(selectedParamValue As String) As ResumableSub

beelze69 said:

Dim theFunction As ResumableSub=myClass.isMyConditionMet("SomeValue") <---

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beelze69 said:

Public selectedParamValue As String

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beelze69 said:

how should database closure be properly implemented in my B4xMainPage ?

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LucaMs said:

Additionally, if your app is Android-only, you can also call CloseDB from the Starter service's Service_TaskRemoved and Service_Destroy events, in addition to what has already been written above, not as an alternative.

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Public Sub CloseDB
    SQL.Close
End Sub

Sub Service_TaskRemoved
'This event will be raised when the user removes the app from the recent apps list.
    CloseDB
End Sub

Sub Service_Destroy
 
    CloseDB
End Sub

LucaMs said:

[I assume you know: there is no need to copy the database file in asynchronous mode and call with Wait For, unless you want to display an animation, progress bar or animated splash screen at the same time]

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Sub Service_Create
    'This is the program entry point.
    'This is a good place to load resources that are not specific to a single activity.
    SafeDirectory = RTP.GetSafeDirDefaultExternal("")
 
    If File.Exists(SafeDirectory, DBName) = False Then
        Wait For (File.CopyAsync(File.DirAssets, DBName, SafeDirectory, DBName)) Complete (Success As Boolean) 'File.DirInternal
        '    ToastMessageShow($"DB Copied = ${Success}"$, False)
    
'        Log("Success: " & Success)
    End If
 
    ConnectToDatabase
    Wait For SQLite_Ready (Success As Boolean)
End Sub

LucaMs said:

You could also close the DB in the B4XPage_Disappear event and reopen it in B4XPage_Appear, if you really want to be "sure" that it is closed;

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LucaMs said:

initialization (not copying) should take very little time, acceptable.

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Private Sub B4XPage_CloseRequest As ResumableSub
'You can see the list of page related events in the B4XPagesManager object. The event name is B4XPage.
'Called when the Page is closed

Set myClass=nothing
End Sub

beelze69 said:

1) Requesting you to give an example of how do I initialize the database in a B4xPage..

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beelze69 said:

SQL.Initialize( SafeDirectory, DBName, False)

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beelze69 said:

2) How do I release the class instance in b4XPage?

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beelze69 said:

I am personally not sure as to how it will function since my application has 'multiple B4XPages' and since 'B4XPages always remain in memory' , I am not too sure as to how will Android function especially if I invoke DBClose for every pages's B4xPage_Disappear[invoked whenever a Page disappears] and open the database in every page's B4xPage_Appear [invoked when a Page appears] event - as an end-user will keep 'sifting through the pages at will' while the app is running.

Requesting for further guidance on this.

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LucaMs said:

View attachment 151123

The above means that you have declared the SQL database (much better name: DB) in the Starter. You also wrote CloseDB in that service.

Instead, everything related to the DB, including declaration, initialization, opening, closing and queries, should be written in the class that manages the DB.

In the Starter service you should only write:

B4X:

Sub Service_TaskRemoved
    B4XPages.MainPage.YourDBManagerPublicVariable.CloseDB
End Sub

Sub Service_Destroy
    B4XPages.MainPage.YourDBManagerPublicVariable.CloseDB
End Sub

YourDBManagerPublicVariable is what you named MyClass; better name: DBManager.

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LucaMs said:

B4XPages.MainPage.DBManager = Null

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Private Sub B4xPage_CloseRequest(Root1 As B4XView) 
myClass=Null
End Sub