CODEWITHSUNDEEP
androidrefactoringandroid-custom-view
David T.
David T.

Reputation: 23399

Proper way to draw custom view?

I'm trying to implement a custom view that is created by some data - specifically I am trying to create a revenue projection graph via a custom view.

The way i'm doing this is by having 10 data points, and drawing lines between each data point. (and then also drawing the X and Y axis lines).

I was thinking about creating a view that encapsulates the 10 coordinates, and draw them via the canvas in onDraw(). something like this:

class RevView extends View {
    private List<Point> mPoints;
    public void configurePoints(float[] revenues) { 
        // convert revenues to points on the graph.
    }
    // ... constructor... etc.
    protected void onDraw(Canvas canvas) {
        // use canvas.drawLine to draw line between the points
    }
}

but in order to do so, i think i need the width/height of the view, which isn't rendered until onDraw.

is this the right approach? or am i even supposed to pass in a Points list to the view? Or what's a better way to build this?

Upvotes: 0

Views: 92

Answers (2)

itscap
itscap

Reputation: 23

You should use onMeasure() method which is called before onDraw() method, so you'll be able to get your view dimensions like this:

@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
    int width = measureWidth(widthMeasureSpec);
    int height = measureHeight(heightMeasureSpec);
}

You should avoid getting View dimensions directly in onDraw() method because it will be called many times a second

Upvotes: 1

LonelyCpp
LonelyCpp

Reputation: 2673

You should override the onMeasure() method which will be called before onDraw().

https://developer.android.com/reference/android/view/View.html#onMeasure(int,%20int)

Measure the view and its content to determine the measured width and the measured height.

Upvotes: 2

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