Android: why setVisibility(View.GONE); or setVisibility(View.INVISIBLE); do not work

I see quite a few things wrong. For starters, you don't have your magic button defined and there is no event handler for it.

Also you shouldn't use:

dp2.setVisibility(View.GONE);
dp2.setVisibility(View.INVISIBLE); 

Use only one of the two. From Android documentation:

View.GONE This view is invisible, and it doesn't take any space for layout purposes.

View.INVISIBLE This view is invisible, but it still takes up space for layout purposes.

In your example, you are overriding the View.GONE assignment with the View.INVISIBLE one.

---

Try replacing:

final DatePicker dp2 = new DatePicker(this)

with:

DatePicker dp2 = (DatePicker) findViewById(R.id.datePick2);  

Similarly for other widgets:

    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        LinearLayout ll = new LinearLayout(this);
        ll.setOrientation(LinearLayout.VERTICAL);

        final DatePicker dp2 = new DatePicker(this);
        final Button btn2 = new Button(this);
        final Button magicButton = new Button(this);
        final TextView txt2 = new TextView(TestActivity.this);

        dp2.setVisibility(View.GONE);
        btn2.setVisibility(View.GONE);
        btn2.setText("set Date");

        btn2.setOnClickListener(new View.OnClickListener() {
            public void onClick(View arg0) {
                txt2.setText("You selected "
                    + dp2.getDayOfMonth() + "/" + (dp2.getMonth() + 1) 
                    + "/" + dp2.getYear());
            }
        });

        magicButton.setText("Magic Button");
        magicButton.setOnClickListener(new View.OnClickListener()    
            public void onClick(View arg0) {
                dp2.setVisibility(View.VISIBLE);
                btn2.setVisibility(View.VISIBLE);
            }
        });

    ll.addView(dp2);
    ll.addView(btn2);
    ll.addView(magicButton);
    ll.addView(txt2);

    setContentView(ll);
}

Today I had a scenario, where I was performing following:

myViewGroup.setVisibility(View.GONE);

Right on the next frame I was performing an if check somewhere else for visibility state of that view. Guess what? The following condition was passing:

if(myViewGroup.getVisibility() == View.VISIBLE) {
    // this `if` was fulfilled magically
}

Placing breakpoints you can see, that visibility changes to GONE, but right on the next frame it magically becomes VISIBLE. I was trying to understand how the hell this could happen.

Turns out there was an animation applied to this view, which internally caused the view to change it's visibility to VISIBLE until finishing the animation:

public void someFunction() {
    ...
    TransitionManager.beginDelayedTransition(myViewGroup);
    ...

    myViewGroup.setVisibility(View.GONE);
}

If you debug, you'll see that myViewGroup indeed changes its visibility to GONE, but right on the next frame it would again become visible in order to run the animation.

So, if you come across with such a situation, make sure you are not performing an if check in amidst of animating the view.

You can remove all animations on the view via View.clearAnimation().

You can think it as a CSS style visibility & display.

<div style="visibility:visible; display:block">
    This is View.VISIBLE : Content is displayed normally.
</div>

<div style="visibility:hidden; display:block">
    This is View.INVISIBLE : Content is not displayed, but div still takes up place, but empty.
</div>

<div style="display:none">
    This is View.GONE : Container div is not shown, you can say the content is not displayed.
</div>