android - Show DialogFragment with animation growing from a point

Question

I'm showing a DialogFragment when the user taps on a row in a ListView. I'd like to animate the showing of the dialog so that it grows from the center of the row. A similar effect can be seen when opening a folder from the launcher.

One idea that I've had is a combination of TranslateAnimation and ScaleAnimation. Is there another way?

Answer 1

Being DialogFragment a wrapper for the Dialog class, you should set a theme to your base Dialog to get the animation you want:

public class CustomDialogFragment extends DialogFragment implements OnEditorActionListener
{
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
        Bundle savedInstanceState) 
    {
        return super.onCreateView(inflater, container, savedInstanceState);
    }

    @Override
    public Dialog onCreateDialog(Bundle savedInstanceState) 
    {
        // Set a theme on the dialog builder constructor!
        AlertDialog.Builder builder = 
            new AlertDialog.Builder( getActivity(), R.style.MyCustomTheme );

        builder  
        .setTitle( "Your title" )
        .setMessage( "Your message" )
        .setPositiveButton( "OK" , new DialogInterface.OnClickListener() 
            {      
              @Override
              public void onClick(DialogInterface dialog, int which) {
              dismiss();                  
            }
        });
        return builder.create();
    }
}

Then you just need to define the theme that will include your desired animation. In styles.xml add your custom theme:

<style name="MyCustomTheme" parent="@android:style/Theme.Panel">
    <item name="android:windowAnimationStyle">@style/MyAnimation.Window</item>
</style>

<style name="MyAnimation.Window" parent="@android:style/Animation.Activity"> 
    <item name="android:windowEnterAnimation">@anim/anim_in</item>
    <item name="android:windowExitAnimation">@anim/anim_out</item>
</style>    

Now add the animation files in the res/anim folder:

( the android:pivotY is the key )

anim_in.xml

<?xml version="1.0" encoding="utf-8"?>
<set xmlns:android="http://schemas.android.com/apk/res/android">
    <scale
        android:interpolator="@android:anim/linear_interpolator"
        android:fromXScale="0.0"
        android:toXScale="1.0"
        android:fromYScale="0.0"
        android:toYScale="1.0"
        android:fillAfter="false"
        android:startOffset="200"
        android:duration="200" 
        android:pivotX = "50%"
        android:pivotY = "-90%"
    />
    <translate
        android:fromYDelta="50%"
        android:toYDelta="0"
        android:startOffset="200"
        android:duration="200"
    />
</set>

anim_out.xml

<?xml version="1.0" encoding="utf-8"?>
<set xmlns:android="http://schemas.android.com/apk/res/android">
    <scale
        android:interpolator="@android:anim/linear_interpolator"
        android:fromXScale="1.0"
        android:toXScale="0.0"
        android:fromYScale="1.0"
        android:toYScale="0.0"
        android:fillAfter="false"
        android:duration="200" 
        android:pivotX = "50%"        
        android:pivotY = "-90%"        
    />
    <translate
        android:fromYDelta="0"
        android:toYDelta="50%"
        android:duration="200"
    />
</set>

Finally, the tricky thing here is to get your animation grow from the center of each row. I suppose the row is filling the screen horizontally so, on one hand the android:pivotX value will be static. On the other hand, you can't modify the android:pivotY value programmatically.

What I suggest is, you define several animations each of which having a different percentage value on the android:pivotY attribute (and several themes referencing those animations). Then, when the user taps the row, calculate the Y position in percentage of the row on the screen. Knowing the position in percentage, assign a theme to your dialog that has the appropriate android:pivotY value.

It is not a perfect solution but could do the trick for you. If you don't like the result, then I would suggest forgetting the DialogFragment and animating a simple View growing from the exact center of the row.

Good luck!