Java - 淡入淡出和显示图像的不同方法

Question

I'm starting to learn Java and i came across an excersize where i need to fade away one image and display by fading in another image.

My solution to this excersize is to have one imageView and fading out the first image, then switching the image source to the second image and fading the imageView in so it should display the new image. Doing that so it will display all the images i want by fading out then in with a new image.

this is my code for the program:

public void fade(View view){

    ImageView simpsonImageView = findViewById(R.id.simpsonsImageView);

    simpsonImageView.animate().alpha(0f).setDuration(3000);
    simpsonImageView.setImageResource(R.drawable.bart);
    simpsonImageView.animate().alpha(1f).setDuration(3000);
    simpsonImageView.animate().alpha(0f).setDuration(3000);
    simpsonImageView.setImageResource(R.drawable.lisa);
    simpsonImageView.animate().alpha(1f).setDuration(3000);
}

Now i have seen in the tutorial i'm learning from that the tutor used different imageView for each image. I wanted to know which solution is correct or at least acceptable amoung these two. Or it dosent really matter and that both solutions are fine.

Answer 1

There is one thing which you can only achieve when using two ImageView s: you can crossfade the two images so that the screen is never entirely empty.

In the context of your exercise however, you only want to exchange images sequentially.

From a performance point of view, one ImageView may be better than two because it will obviously take less memory and CPU time but I doubt that this will have a noticeable impact on modern devices.

So as long as you don't animate lots of pictures simultaneously (think of football teams instead of the Simpsons), both solutions are fine.

Please note that with your code as-is there will be no animation visible at all and the ImageView will appear to only show the second picture. This is because animate() triggers an animation but it does not wait until the animation is finished. So you need to work with an AnimationListener or use Handler.postDelayed() to swap pictures and start the next animation only as soon as the previous one is finished.