android canvas - can i have multiple draw methods?

I have made my own canvas class which extends an imageView. My onDraw() method draws out the users gps position and I keep calling this onDraw method every time the user moves. My problem is I also want to draw out a gps trail which only needs to be drawn once (doesnt need to be updated when a user moves). I am wondering is it possible to have more than 1 onDraw method or is there any way of separating 1) the user location and 2) the gps trail??

My开发者_JAVA技巧 reason is I do not want to waste memory by redrawing the gps route everytime the users gps position changes. It is a waste.

Have you seen performance take a hit? If not, don't worry about it. I would think that this would be wasting CPU cycles if anything... not memory. So if the app seems fast enough already, don't worry about optimizing it.

If your app is a bit laggy, and you've found that the trail is the bottleneck... I would suggest caching it into a bitmap. This way, you will still have to draw the trail, but you will not have to calculate the coordinates of the trail on each frame.

I have had to solve a somewhat similar problem recently and I'll explain briefly what I did in case it's of any help.

What you can do is use multiple overlapping Views, where one may contain the background graphics that you don't want to redraw often, and a foreground View that contains the graphics that are frequently updated. Then, to gain performance, you can design the background View's onDraw() so that it is backed by a Bitmap that you then retain as a class variable. In the very first onDraw() of your background graphics, you do the relatively slow drawing to Canvas. In subsequent calls to onDraw(), you simply draw that Bitmap to Canvas.

I've just done this myself. Basically what my application does is display a number of graphical gauges. Those gauges have lots of graphics that are drawn just once (gauge face, number legends), and the pointer graphic that needs to be redrawn over and over as the model data changes. First of all, I split the background graphics and moving foreground graphics into separate overlapping Views. Now, invalidating and redrawing the foreground pointer graphic of course causes anything it overlaps to be invalidated too, so the onDraw() method for the background graphics View is being called each time the pointer View is redrawn. The background View only needs to draw the background graphics once, but retains the Bitmap that backs the canvas, and in subsequent onDraw() calls it draws this bitmap back to Canvas (which is a lot faster than initially creating the graphics using Path() objects).

Bitmap bm;


....

protected void onDraw(Canvas canvas){
    if(null==bm){
        bm=Bitmap.createBitmap(getMeasuredWidth(),getMeasuredHeight(),Bitmap.Config.ARGB_8888);
        // do your slow vector graphics drawing to Canvas here
    }
    Paint drawPaint = new Paint();
    drawPaint.setAntiAlias(false);
    drawPaint.setFilterBitmap(false);
    drawPaint.setDither(false);
    canvas.drawBitmap(bm, 0, 0, drawPaint);
}

Well, there can't be more than 1 onDraw method, assuming that I understood your question correctly. You will need to think about alternate approaches about how to handle this.

@DeeV suggested, that can be a solution for you.