单击按钮显示/隐藏ImageView

Question

I have a RelativeLayout completely created within java, not using xml layout. I have a few buttons on the left if my screen. I want to click on one button and show a default image from my res/drawable next to the button and make it disappear again on second click. What I have tried was toggling the visibility but my onClick() raises a FATAL EXCEPTION, NullPointer Exception.

This is my code so far. Hardcoded the image shows right when I set picview.setVisibility(View.INVISIBLE); by hand. What I am doing wrong in the onClick() ?

    private ImageView picview;

        //*snip* loads of other code

    //Show Image Button
    ImageButton show_pic = new ImageButton(this);
    show_pic.setBackgroundColor(Color.WHITE);
    show_pic.setOnClickListener(new OnClickListener()
    {

        @Override
        public void onClick(View v) {
            if(picview.getVisibility() == View.INVISIBLE)
             {
             picview.setVisibility(View.VISIBLE);
             } 
            else if (picview.getVisibility() == View.VISIBLE)
             {
             picview.setVisibility(View.INVISIBLE);
             }          
            }

    });

    params = new RelativeLayout.LayoutParams(40, 40);
    params.topMargin = 10;
    params.leftMargin = 10;
    params.addRule(RelativeLayout.BELOW, button2_id);
    rl.addView(show_pic, params);

    //Imageview loaded from drawable
    ImageView picview = new ImageView(this);
    params = new RelativeLayout.LayoutParams(200, 400);
    params.topMargin = 0;
    params.leftMargin = 30;
    params.addRule(RelativeLayout.RIGHT_OF, button2_id);
    picview.setImageResource(R.drawable.my_image);
    picview.setVisibility(View.INVISIBLE);
    rl.addView(picview, params);

    this.setContentView(rl);

Answer 1

You are accidentally creating two copies of picview . Shorten this line:

ImageView picview = new ImageView(this);

To:

picview = new ImageView(this);

(Your field variable private ImageView picview; never changed from null , so when you clicked your Button you see the NullPointerException...)

Answer 2

change show_pic.setOnClickListener(new OnClickListener() to

show_pic.setOnClickListener(new View.OnClickListener()