CODEWITHSUNDEEP
androidcanvaspathdrawing
Igor SKRYL
Igor SKRYL

Reputation: 302

Android. Canvas. Dinamically add path point

I am trying to add points to the Path and drawing line between them, but nothing appear.

I have custom view:

public class BreakDownBar extends View {
private List<Point> points = new ArrayList<>();
private Path path = new Path();
private Paint p = new Paint();

public BreakDownBar(Context context) {
    super(context);
}

public BreakDownBar(Context context, AttributeSet attrs) {
    super(context, attrs);
    p.setStrokeWidth(5);
    p.setStyle(Paint.Style.STROKE);
}

public void addPoint(Point point) {
    points.add(point);
    path.rewind();
    reDraw();
}

public void startPoint(Point point) {
    points.add(point);
}

private void reDraw() {
    Canvas canvas = new Canvas();
    path.moveTo(points.getFirst().getX(), points.getFirst().getY());
    for (int i = 1; i < points.size(); i++) {
        path.lineTo(points.get(i).getX(), points.get(i).getY());
    }


    canvas.drawPath(path, p);
    canvas.drawColor(Color.BLACK);
    draw(canvas);
    invalidate();
}

}

Point class:

public class Point {
private float x, y;

...getters and setters
}

While adding new points to the List I can see thought the expected result in the log, but nothing happen on the screen.

What I missed to make line appear on the screen?

Upvotes: 1

Views: 2711

Answers (1)

MatPag
MatPag

Reputation: 44901

You are using a bad logic to draw the line, if you call invalidate() you will request a call to draw() and this will reset your canvas.

Try with this version of your class:

public class BreakDownBar extends View {
    private List<Point> points = new ArrayList<>();
    private Path path = new Path();
    private Paint p = new Paint();

    public BreakDownBar(Context context) {
        super(context);
        p.setStrokeWidth(5);
        p.setStyle(Paint.Style.STROKE);
        p.setColor(Color.BLACK);
    }

    public void addPoint(Point point) {
        points.add(point);
        //this will request a call to draw(canvas) method
        invalidate();
    }

    @Override
    public void draw(Canvas canvas) {
        super.draw(canvas);
        //move to the first point in the list
        path.moveTo(points.get(0).getX(), points.get(0).getY());
        for (int i = 1; i < points.size(); i++) {
            path.lineTo(points.get(i).getX(), points.get(i).getY());
        }
        canvas.drawPath(path, p);
    }
}

Then in your code you can simply do

BreakDownBar bar = new BreakDownBar(context);
bar.addPoint(new Point(100f, 200f))
bar.addPoint(new Point(200f, 300f))
bar.addPoint(new Point(400f, 200f))

Let me know if this works for you.

Upvotes: 4

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