Other [quiz] Find the bug

Erel · Jul 13, 2015

B4X:

Sub Process_Globals
   Public Image As Bitmap 'public image
   Private SQL1 As SQL 'private sql object
End Sub

Sub Activity_Create(FirstTime As Boolean)
   If FirstTime Then
     Image = LoadBitmap(File.DirAssets, "Image.jpg")
     SQL1.Initialize(File.DirInternal, "1.db", True)
   End If
End Sub

Solution: https://www.b4x.com/android/forum/threads/quiz-find-the-bug.56132/page-2#post-353562

Erel · Jul 13, 2015

sorex said:
Image is an existing type in java or something?

No.

sorex · Jul 13, 2015

I never work with multiple activities and I don't have a clue where to look so I give up

Mark Read · Jul 13, 2015

Just a thought, is "Image" a reserved word as it is in green?

Erel · Jul 13, 2015

mark35at said:
Just a thought, is "Image" a reserved word as it is in green?

No. It is green because the forum parser treats it as B4J Image type.

imbault · Jul 13, 2015

So, well, I will exclude the 2 intializes from the FirstTime:

B4X:

Sub Activity_Create(FirstTime As Boolean)
   If FirstTime Then
   End If
     Image = LoadBitmap(File.DirAssets, "Image.jpg")
     SQL1.Initialize(File.DirInternal, "1.db", True)
End Sub

eurojam · Jul 13, 2015

Now I have a second activity which will load the image in an imageview. It still working like a charm.......no crash....

so the error is not as obvious like this one is

RandomCoder · Jul 13, 2015

My guess is that because the image is loaded only on the FirstTime there could be an occasion where the Main Activity is destroyed along with the bitmap resulting in the image having a Null value? But I'm not sure this stacks up becuase it is defined as a process Global and so should not get destroyed when still being used by other Activities???

Erel · Jul 13, 2015

imbault said:
So, well, I will exclude the 2 intializes from the FirstTime:

It is a mistake to initialize SQL when FirstTime is not True. It will cause the SQL connection to be initialized multiple times (for example when the user changes orientation).

RandomCoder said:
My guess is that because the image is loaded only on the FirstTime there could be an occasion where the Main Activity is destroyed along with the bitmap resulting in the image having a Null value? But I'm not sure this stacks up becuase it is defined as a process Global and so should not get destroyed when still being used by other Activities???

Almost, but not there yet...

Jaames · Jul 13, 2015

~~If you want to reload bitmap with other file, from another activity, it will not be possible~~

B4X:

 Main.Image = LoadBitmap(File.DirAssets,"Image2.jpg")

Not true , sorry

If you once change the image, and later exit the app, next time you start the app, image won't be default one

DonManfred · Jul 13, 2015

Erel said:
Image = LoadBitmap(File.DirAssets, "Image.jpg")

It must be image.jpg! Files in File.DirAssets must be lowercase

Jaames · Jul 13, 2015

DonManfred said:
It must be image.jpg! Files in File.DirAssets must be lowercase

They can , you can use name you want, b4a will internally lowercase them.

DonManfred · Jul 13, 2015

Dammit

imbault · Jul 13, 2015

Erel said:

B4X:

Sub Process_Globals
   Public Image As Bitmap 'public image
   Private SQL1 As SQL 'private sql object
End Sub

Sub Activity_Create(FirstTime As Boolean)
   If FirstTime Then
     Image = LoadBitmap(File.DirAssets, "Image.jpg")
     SQL1.Initialize(File.DirInternal, "1.db", True)
   End If
End Sub

The bug is : this App will do just nothing and show nothing, except initializing a db without any structure and loading an image.

RandomCoder · Jul 13, 2015

Erel said:
"RandomCoder said:
My guess is that because the image is loaded only on the FirstTime there could be an occasion where the Main Activity is destroyed along with the bitmap resulting in the image having a Null value? But I'm not sure this stacks up becuase it is defined as a process Global and so should not get destroyed when still being used by other Activities???"

Almost, but not there yet...

Ok, so is it possible that if not using the image on another Activity and the Main Activity gets destroyed then there is a time when we no longer have the Image declared. Attempting to use the Image or load a Bitmap from another Activity will result in an error because Main no longer exists and so the reference to Main.Image throws an error?

Erel · Jul 14, 2015

Solution

The problem is with the image:

B4X:

Sub Process_Globals
   Public Image As Bitmap 'public image
   Private SQL1 As SQL 'private sql object
End Sub

Sub Activity_Create(FirstTime As Boolean)
   If FirstTime Then
     Image = LoadBitmap(File.DirAssets, "Image.jpg")
     SQL1.Initialize(File.DirInternal, "1.db", True)
   End If
End Sub

The reason that this image is public is that we plan to use it from other activities.

For example:

B4X:

'Activity2
Sub Activity_Create(FirstTime As Boolean)
 Activity.SetBackgroundImage (Main.Image)
End Sub

During development everything will look fine. The application will always start from the main activity and the image will live as long as the process lives.

However it will eventually fail when it is installed on the user device.
The user will press on the home key when the second activity is visible. The process will move to the background.
At some point the OS will kill the process as it is in the background.
Later when the user returns to the app the process will start from the second activity.
Main activity was not created yet so its Activity_Create wasn't executed. This means that the image is not initialized at that point.

You can see it during development with this developer setting:

Run your app in Release mode, switch to the second activity, press on home and start a different app. Return to your app and in most cases it will start from the second activity directly.

To solve this issue you can add a code module that holds all the public resources:

B4X:

Sub Process_Globals
   Public Image As Bitmap
   Private alreadyInitialized As Boolean
End Sub


Public Sub Init
   If alreadyInitialized = False Then
     Image = LoadBitmap(File.DirAssets, "Image.png")
    'all other resources as well
     alreadyInitialized = True
   End If
End Sub

Now you should call this Init sub from Activity_Create (and Service_Create) of all activities and services.

Related quiz: https://www.b4x.com/android/forum/threads/37899/#content

Alberto Michelis · Jul 29, 2015

Suppouse all the variables I need became from procesess that can't be moved to the Code module (add-billing, etc)
It is ok to use the Code module just to keep the variables in the Sub Process_Globals
And set that variables from other modules with

MyCodeModule.Myvarible = xxx

Does this variables will keep its values without setting it again in Sub init? mhhh I think not.

And how if I use a service to hold the Process variables?

DonManfred · Jul 29, 2015

Alberto Michelis said:
Suppouse all the variables I need became from procesess that can't be moved to the Code module (add-billing, etc)
It is ok to use the Code module just to keep the variables in the Sub Process_Globals
And set that variables from other modules with

MyCodeModule.Myvarible = xxx

Does this variables will keep its values without setting it again in Sub init? mhhh I think not.

And how if I use a service to hold the Process variables?

Is THIS your answer to the QUIZ? BTW: Erel already posted the answer. No need to guess the answer

Alberto Michelis · Jul 29, 2015

You didn read my post or its difficult for me to make me undestand, bad luck.
New q:

How if I use a Service module to hold all the Process variables?
May be I have to use Service.StartForeground?

DonManfred · Jul 29, 2015

I did real you post. That why i asking what i ask

So you are Not answering the Quiz but asking offtopic questions?

You Know that this is the WRONG PLACE to ask questions?

Hint: Considered to create a New thread for yor question instead of asking at the WRONG place

Alberto Michelis · Jul 29, 2015

Sory I dont know that this is the WRONG PLACE to ask questions
Why is it wrong, Im asking about the Thread, why to start another?

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