CODEWITHSUNDEEP
androidandroid-canvasandroid-view
Prashanth
Prashanth

Reputation: 156

How to draw views using Canvas Android?

I am trying to draw views dynamically on click of button.On clicking the button,I got an illegal state exception saying; the specified view already has a parent.

Is this the right way to create views dynamically?

 @Override
    protected void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);


        draw = new DrawView(this);

        relativeLayout = new RelativeLayout(this);
        createButton = new Button(this);
        relativeLayout.addView(createButton);
        setContentView(relativeLayout);

        createButton.setOnClickListener(new OnClickListener()
        {

            @Override
            public void onClick(View arg0)
            {
                relativeLayout.addView(draw);
                setContentView(draw);
            }
        });

    }

public class DrawView extends View
{
    Paint paint;

    public DrawView(Context context, AttributeSet attrs)
    {
        super(context, attrs);
    }

    public DrawView(Context context)
    {
        super(context);
        paint = new Paint();
    }

    @Override
    protected void onDraw(Canvas canvas)
    {
        super.onDraw(canvas);
        paint.setColor(Color.BLACK);
        paint.setStrokeWidth(3);
        canvas.drawRect(30, 30, 80, 80, paint);
        paint.setStrokeWidth(0);
        paint.setColor(Color.CYAN);
        canvas.drawRect(33, 60, 77, 77, paint );
        paint.setColor(Color.YELLOW);
        canvas.drawRect(33, 33, 77, 60, paint );
    }
}

Upvotes: 3

Views: 7665

Answers (2)

android_dev
android_dev

Reputation: 1477

The problem with this 

relativeLayout.addView(draw);
setContentView(draw);

You can add a view to only one layout at a time. You can't add the same View to multiple ViewGroups (Layouts). The code above add the 'draw' View as a child of the 'relativeLayout' when sets it as the content View (for whatever class 'this.' is).

You can add the View with either:

 relativeLayout.addView(draw);

or 

 setContentView(draw);

Upvotes: 1

Navjot
Navjot

Reputation: 1294

Replace

     relativeLayout.addView(draw);
     setContentView(draw);

with 

     relativeLayout.addView(draw);
     relativeLayout.invalidate();

this will add your view into relativeLayout and invalidate it to refresh screen

Upvotes: 3

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