Android – Page 3 – Alejandro G. Carlstein Ramos Mejia Blog

Alejandro G. Carlstein Ramos Mejia July 27, 2011 August 4, 2011 About Programming / Android

Bitmap Zombieee

When working with bitmaps, there is an issue that shows in the device but not in the
android emulator.

I was always thinking that after using the method empty(), I did not have to worry about the reference variable no more. I did this assumption because in the android developers guide like establish that “Free the native object associated with this bitmap, and clear the reference to the pixel data.” (http://developer.android.com/reference/android/graphics/Bitmap.html). Therefore, I was assuming that the Garbage Collector would take care of it:

Bitmap bitmap = null;
bitmap = BitmapFactory.decodeFile(uri.getPath());
if (bitmap != null) {
   ...
   bitmap.recycle();
}
..
However, I was proven wrong after repeated problem I was facing when running the program inside the device.

After searching online for hours, I found out that the bitmap reference have to be set to null after using the recycle() method:
Bitmap bitmap = null;
bitmap = BitmapFactory.decodeFile(uri.getPath());
if (bitmap != null) {
   ...
   bitmap.recycle();
   bitmap = null;
}
...
Just to clarify, there is no obligation in using the recycle() method; however, it is a good practice using it.
Another thing to have in consideration is that when you pass a bitmap  object to another object, you need to know if that object would make a  copy or use the bitmap object that you provide. If the bitmap object  provided is the one that will be use, then make sure to not recycle or  null the bitmap object else you will get a run-time error.
Bitmap bitmap = null;
bitmap = BitmapFactory.decodeFile(uri.getPath());
if (bitmap != null) {
    imageButtonPicture.setImage(bitmap); // do not null or recycle bitmap
}
...

No External Storage Issue

I notice an error when I was trying to access to the external storage.
The method getRoot() that I implemented was returning null instead of the external storage directory:

public static File getRoot() {
    Log.d(TAG, 'getRoot()');
    return (ExternalStorage.isAvailable()) ? Environment.getExternalStorageDirectory() : null;
}

After thinking, I remember that I choose the option Disk drive instead of HTC Sync as I always do:

I reconnected the device and choose HTC Sync instead of Disk Drive.
This solve the problem; however, I must add the steps needed to working with this kind of issues. I was not expected for the external storage to be unavailable if connected to the PC.

Working with SQLite Cursors

A common mistake is the improper way to use cursors. It is very common to use a cursor and forget to close it. This produce an IllegalStateException.

A code similar to the following code example will produce an error the moment you leave the activity:

private void readContactData(long contactDataId) {
   Log.d(TAG, 'readContactData()');
   dbContact.open();
   Cursor cursor = dbContact.getContact(contactDataId);
   if (cursor.moveToFirst()) {
     ...
   } else {
     ...
   }
   dbContact.close();
   ...
}
The         problem         is         that         you         are         not         closing         the         cursor         properly.

You         could         try         the         following         variable         of         the         previous         code:
private void readContactData(long contactDataId) {
   Log.d(TAG, 'readContactData()');
   dbContact.open();
   Cursor cursor = dbContact.getContact(contactDataId);
   if (cursor.moveToFirst()) {
     ...
   } else {
     ...
   }
   cursor.close();
   dbContact.close();
   ...
}

However,                  there         are         cases         that         this         code         produce         a         warning         when         cursor         calls         the                  method         finalizer().         This         seems         to         be         a         problem         with         Droid         2.
This         method         seems         to         work         better:
private void readContactData(long contactDataId) {
    Log.d(TAG, 'readContactData()');
    Cursor cursor = null;
    try{
        dbContact.open();
        cursor = dbContact.getContact(contactDataId);
        if (cursor.moveToFirst()) {
            ...
        } else {
            ...
        }
        dbContact.close();
    }finally{
        if (cursor != null){
            cursor.deactivate();
            cursor.close();
        }
    }
}
Finally,         there         is         always         the         option         of         using         startManagingCursor();         however,         this         will         be         deprecated         and         replaced         with         CursorLoader class         when         using         API         11.