Question

I’m having some troubles with a slideshow I’m building.

I’ve created 2 animations in xml for fade in and fade out:

fadein.xml

    <?xml version="1.0" encoding="UTF-8"?>
       <set xmlns:android="http://schemas.android.com/apk/res/android">
         <alpha android:fromAlpha="0.0" android:toAlpha="1.0" 
          android:interpolator="@android:anim/accelerate_interpolator" 
          android:duration="2000"/>
     </set>

fadeout.xml

    <?xml version="1.0" encoding="UTF-8"?>
       <set xmlns:android="http://schemas.android.com/apk/res/android">
         <alpha android:fromAlpha="1.0" android:toAlpha="0.0" 
          android:interpolator="@android:anim/accelerate_interpolator" 
          android:duration="2000"/>
     </set>

What Im’trying to do, is to change images from an ImageView using the fade effect, so the currently displayed image will fade out, and another one will fade in.
Considering that I have an image already set, I can fadeout this Image without problem, with this:

    Animation fadeInAnimation = AnimationUtils.loadAnimation(this, R.anim.your_fade_in_anim);
    imageView.startAnimation(fadeoutAnim);

But then, I set the next image to be displayed:

    imageView.setImageBitmap(secondImage);

It just shows up in the imageView, and when i set the animation it hides the image, the fade it in… Is there any way to fix that, I mean, when I do imageView.setImageBitmap(secondImage); command, the image do not shows up immediately, and only when the fade in animation is executed?

Answer 1

To implement this the way you have started, you’ll need to add an AnimationListener so that you can detect the beginning and ending of an animation. When onAnimationEnd() for the fade out is called, you can set the visibility of your ImageView object to View.INVISIBLE, switch the images and start your fade in animation – you’ll need another AnimationListener here too. When you receive onAnimationEnd() for your fade in animation, set the ImageView to be View.VISIBLE and that should give you the effect you’re looking for.

I’ve implemented a similar effect before, but I used a ViewSwitcher with 2 ImageViews rather than a single ImageView. You can set the “in” and “out” animations for the ViewSwitcher with your fade in and fade out so it can manage the AnimationListener implementation. Then all you need to do is alternate between the 2 ImageViews.

Edit:
To be a bit more useful, here is a quick example of how to use the ViewSwitcher. I have included the full source at https://github.com/aldryd/imageswitcher.

activity_main.xml

    <ViewSwitcher
        android:id="@+id/switcher"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_alignParentTop="true"
        android:layout_centerHorizontal="true"
        android:inAnimation="@anim/fade_in"
        android:outAnimation="@anim/fade_out" >

        <ImageView
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:scaleType="fitCenter"
            android:src="@drawable/sunset" />

        <ImageView
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:scaleType="fitCenter"
            android:src="@drawable/clouds" />
    </ViewSwitcher>

MainActivity.java

    // Let the ViewSwitcher do the animation listening for you
    ((ViewSwitcher) findViewById(R.id.switcher)).setOnClickListener(new View.OnClickListener() {

        @Override
        public void onClick(View v) {
            ViewSwitcher switcher = (ViewSwitcher) v;

            if (switcher.getDisplayedChild() == 0) {
                switcher.showNext();
            } else {
                switcher.showPrevious();
            }
        }
    });