Android: Declaring static bitmaps? Yay or nay?
Somebody recently commented on my code where I declare the following:
private Bitmap splashBackground;
private Bitmap lightDot;
private static Bitmap scaledBackground;
private static Bitmap scaledLightDot;
They advised me against declaring satic Bitmaps.
However, I've tried everything and my code doesn't work unless I declare them as static.
Also, "public static Bitmap createScaledBitmap (Bitmap src, int dstWidth, int dstHeight, boolean filter)" seems to appear on the official Android Developer site so I'm a bit confused about what I should and shouldn't be doing.
Any pointers would be appreciated - thank you
Edit: For clarification:
When I remove the static from my declaration, then by the time I get to my onDraw() method, the scaled bitmap is null. (I am creating the scaled bitmap object in an initialise() method and once it's been created, it is valid (ie, not null) - but then seems to become null at onDraw unless I declare it as static.
I am calling my initialise() method from my activity class.
Edit: More code as requested.
My OnCreate method: As you can see, I'm passing my screen height and width over so I can create my scaled bitmaps
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
displaySplashScreen= new SplashScreen(this);
requestWindowFeature(Window.FEATURE_NO_TITLE);
getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN, WindowManager.LayoutParams.FLAG_FULLSCREEN);
// set View
setContentView(new SplashScreen(this));
WindowManager w = getWindowManager();
Display d = w.getDefaultDisplay();
int width=d.getWidth();
int height=d.getHeight();
displaySplashScreen.initialise(width, height);
}
My initalise method:
public void initialise(int w, int h)
{
//Get width and height (passed in from Activity)
vwidth=w;
vheight=h;
//Create pre-scaled bitmaps
scaledBackground = Bitmap.createScaledBitmap(splashBackground, vwidth, vheight, true);
scaledLightDot = Bitmap.createScaledBitmap(lightDot, vwidth, vheight, true);
}
I could add also that if I use a standard variable in the same way (say int number;) and set it in initalise (number = 5;), then number is only equal to 5in my initialise method. If I log it from onDraw() it will always repeatedly return '0'!! It's baffling.
Thanks everyone so far, please let me know if more code is required......
In general, utilizing static for Bitmap s is a very bad idea. There are a lot of good reasons for this, mostly having to do with avoiding memory leaks.
Also, "public static Bitmap createScaledBitmap (Bitmap src, int dstWidth, int dstHeight, boolean filter)" seems to appear on the official Android Developer site ...
This is not a static Bitmap . This is a method call to a class method. Static does not work the same and the return type ( Bitmap ) is not static. What this means is that the method is static and does not require an instance to be called. It will return a Bitmap to be placed in an appropriate variable of your choice.
I am calling my initialise() method from my activity class.
This statement is quite unhelpful. From where in the class is it being called? Is it in onCreate() , onStart() , onResume() , some other custom method? Where and when you choose to do certain things can have a huge effect as to how successful they are.
... but then seems to become null at onDraw unless I declare it as static.
This could be for several possible reasons, and since we don't have any of your code there really isn't a qualified answer. Here are some things to look at.
null . createScaledBitmap() method. EDIT: After reviewing your code
This looks like it may be the culprit. Above, you have...
displaySplashScreen= new SplashScreen(this);
Below, you add...
setContentView(new SplashScreen(this));
This means that you are creating two Splashscreens. One reason why you are getting a null pointer when you are not using static may be because further down the line you use...
displaySplashScreen.initialise(width, height);
But since your contentView is set to a new SplashScreen, you are not actually utilizing that View. To resolve this, make sure you are talking to the same view object. IE
setContentView(displaySplashScreen);
This will at least make sure you are looking at the same object. It is possible that you may have to reorganize a bit depending upon what other things are happening. For instance,
setContentView(displaySplashScreen);
... may have to appear below ...
displaySplashScreen.initialise(width, height);
This is something that you might have to toy with, but I don't see anything else that gives any other immediate indication. Be aware that resolving nullpointerexceptions will often result in revealing more errors in code, at first. Stay the course and resolve each in order.
This line is wrong:
// set View
setContentView(new SplashScreen(this)); // This line is wrong.
Should be this:
// set View
setContentView(displaySplashScreen); // displaySplashScreen is created earlier.
You are created two instances of SplashScreen . You should keep using the same instance.
I vote for nay, this one is a static variable
private Bitmap splashBackground;
private Bitmap lightDot;
private static Bitmap scaledBackground;
private static Bitmap scaledLightDot;
and this one is a static method
public static Bitmap createScaledBitmap (Bitmap src,
int dstWidth, int dstHeight, boolean filter)
static variable is usually declared for a constant and the variable belongs to class not object as an example if you have a class
public class car {
private static colorOfCar;
private numberOfDoor;
}
let's say you have a class car and have 2 variable colorOfCar and numberOfDoor when you create an object porsche and ferrari from car class if you change the number of door it's OK the numberOfDoor in your porsche object and ferrari object will be different, but if you change the colorOfCar both porsche object and ferrari object colorOfCar will be changed because the colorOfCar is a static object that belong to the class not the object.
I hope you understand my explanation. If you find my answer helping you please vote and accept my answer and if you have any other question feel free to ask in the comment, thank you :)
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