Question

I already got my DrawView, but can only draw 1 line at one time. If i try drawing again the last line deletes, how can I “save” them?

Answer 1

The onDraw refreshes the whole canvas. To print multiple lines you may store the lines in a model (e.g. a collection of Line objects):

@Override
public void onDraw(Canvas canvas) {
    for (Line l : lines) {
        canvas.drawLine(l.x1, l.y1, l.x2, l.y2, paint);
    }
}