Question

I already make some search on the forum and on google about initializing and using a static field. But I can’t fix it alone so here is the simplified code:

...
import android.graphics.Canvas;
...

public class MyActivity extends Activity{

...
public static Canvas myCanvas = new Canvas();
public static float myMaxX;
public static float myMaxY;
...

@Override
protected void onCreate(Bundle savedInstanceState) {
    // TODO Auto-generated method stub
    super.onCreate(savedInstanceState);

    ...
    myMaxX = myCanvas.getWidth(); // <=== Error, the app crashes right there
    myMaxY = myCanvas.getHeight();
    ... 
    ...

    }
...
}

Did I miss something ?

Answer 1

Yes!

You need to create a bitmap first:

int w = WIDTH_PX, h = HEIGHT_PX;

BitmapConfig conf = Bitmap.Config.ARGB_8888; // see other conf types
Bitmap bmp = Bitmap.createBitmap(w, h, conf); // this creates a MUTABLE bitmap
Canvas canvas = new Canvas(bmp);

// ready to draw on that bitmap through that canvas

But creating a static Canvas reeks of code smell. I don’t know what you’re trying to do with it, but I don’t think anything good will come of it. You may find you run in to loads of issues around concurrent read/write violations if you’re sharing this canvas between multiple threads.