AlphaAnimation does not work

问题:

I have been looking for a solution to my problem. But my code seems to be ok.

I'll try to explain: I have a TextView with android:alpha="0" in my layout definition. I want (when a image is clicked) show that TextView with an AlphaAnimation, from 0.0f to 1.0f.

My problem is that when I click the image, nothing happens. But the strange thing, is that if I set it's alpha to 1 in the layout definition, and I click the image, I can see the animation (alpha 1 -> alpha 0 -> alpha 1).

What am I doing wrong?

My code:

TextView tv = (TextView) findViewById(R.id.number);

AlphaAnimation animation1 = new AlphaAnimation(0.0f, 1.0f);
animation1.setDuration(1000);
animation1.setFillAfter(true);
tv.startAnimation(animation1);

Thanks in advance.

回答1:

The problem is in android:alpha="0". This property sets transparency of a View http://developer.android.com/reference/android/view/View.html#attr_android:alpha

When alpha property is equal to 0 then animation is changing transparency from 0*0.0f=0 to 0*1.0f=0. When alpha property is set to 1 then animation is changing transparency from 1*0.0f=0 to 1*1.0f=1. That's why in first case you can't see text and in the second everything works as expected.

To make things work you have to set visibility property to invisible in layout xml. And before starting alpha animation call tv.setVisibility(View.VISIBLE);

回答2:

More simple way is presented in this answer:

tv.animate().alpha(1).setDuration(1000);