Difference between setAlpha and setImageAlpha
Solution 1
ImageView.setAlpha(int)
has been renamed to ImageView.setImageAlpha(int)
to avoid confusion with the new method View.setAlpha(float)
introduced in API level 11.
View.setAlpha(float)
is a general method available on all View
s, including ImageView
. It applies the specified opacity to the whole view. To achieve this, by default the system creates a temporary buffer (a hardware layer) where the View is drawn as usual, then the buffer is drawn on the screen with the specified alpha value. It's a two-pass mechanism which requires the initial allocation of a buffer, so it's somewhat slower. See this video for more information and how to change the default behavior: Hidden Cost of Transparency.
It's important to note that ImageView
includes by default an optimization that will avoid this buffer allocation if it has no background, so in practice there will be no performance penalty when calling ImageView.setAlpha(float)
if the ImageView
has no background.
ImageView.setImageAlpha(int)
(and ImageView.setAlpha(int)
) are methods proper to the ImageView
. They control the alpha value which is used to draw the content image (bitmap or other) directly on the screen, with no intermediate pass, so this is the preferred method to use to apply transparency to an image displayed by an ImageView
. Of course if you set a background Drawable on your ImageView
that you also want to be translucent, this method will not produce the expected result.
Solution 2
-
View.setAlpha(float)
accepts a float as input and expects a value in the range 0..1 inclusive. -
ImageView.setAlpha(int)
accepts an int as input and expects a value on the range 0..255 inclusive.ImageView.setAlpha(int)
is deprecated. This is probably because they wanted to remove the conflict with the underlyingView.setAlpha(float)
- As other responders have pointed out
ImageView.setImageAlpha(int)
simply calls through to the deprecatedImageView.setAlpha(int)
. You should expect thatImageView.setAlpha(int)
will be removed in a future API update and should therefore avoid using it.
Solution 3
yes, it is only a naming difference - the current implementation in the Android source in API level 16 is:
/**
* Sets the alpha value that should be applied to the image.
*
* @param alpha the alpha value that should be applied to the image
*
* @see #getImageAlpha()
*/
@RemotableViewMethod
public void setImageAlpha(int alpha) {
setAlpha(alpha);
}
Solution 4
I believe only the naming is a difference. Because setImageAlpha()
is more specific than setAlpha()
. For the View#setAlpha
and ImageView#setAlpha/setImageAlpha
there is not a direct relation.. the View
class has a setAlpha because it could function as a parent of a View#ImageView
so it functions like a container.
With the setAlpha
you could set the opacity of the whole container therefor it needs that method. with the setImageAlpha
you could set the alpha of only the image and not the whole container.
Besides this i can't really think of a reason they have both an alpha method.
kolistivra
Updated on August 17, 2020Comments
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kolistivra almost 4 years
ImageView has two methods related methods: setAlpha and setImageAlpha. The former is available since API level 1, but is deprecated since level 16. The latter is available since level 16. There's also another setAlpha method, from the View class and this is introduced in API level 11.
Is the difference between ImageView#setAlpha and ImageView#setImageAlpha only in the naming? Is there any behavioral difference? What's the relationship between View#setAlpha and ImageView#setAlpha?
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Jose_GD about 10 yearsThis is true, however setAlpha() has a @Deprecated annotation, so it's most probably setImageAlpha() implementation will change in the future
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Milos Vidakovic over 9 yearsyou hit on the key difference between
setAlpha()
andsetImageAlpha()
With the setAlpha you could set the opacity of the whole container therefor it needs that method. with the setImageAlpha you could set the alpha of only the image and not the whole container. -
BladeCoder almost 9 yearsThis answer is ambiguous.
ImageView.setAlpha(int)
is deprecated only because of its name, and it's been renamed toImageView.setImageAlpha(int)
. When you need to apply an alpha filter on an ImageView, it's preferred to usesetImageAlpha(int)
or the deprecatedsetAlpha(int)
because they apply the alpha value directly to the underlyingPaint
which draws the image on the Canvas, while setAlpha(float) creates a temporary buffer where your view is drawn, then the buffer is blend with the rest of the screen with the specified alpha value. -
Gil Moshayof almost 9 yearsThis is the most comprehensive and accurate answer by far. Don't understand why its rated lowest. This should be the accepted answer.
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LarsH over 8 years@CrimsonX: Looking at the source code (e.g. in cania's answer) it appears that the difference in behavior you describe doesn't actually exist. The two methods do the same thing. So it seems that this answer and the comment are incorrect.
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azizbekian over 8 yearsChet Haase clarifies what @BladeCoder pointed out in Google I/O 2013 - Android Graphics Performance video
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Mark over 6 yearsit's worth noting that currently setImageAlpha() does not work well when the resource is an adaptive icon. In that case, use View.setAlpha() instead. issuetracker.google.com/issues/72694861
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Louis CAD about 5 yearsNot really. There's
setAlpha(float alpha)
which takes afloat
, not anint
. Big difference. I mean, not the same thing at all. -
Ashu Kumar about 5 yearsGood point setBackground not produce bad result. This was what i was searching. thanks buddy
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cania over 4 yearsSorry Louis, you failed to see that in ImageView, there was a setAlpha(int alpha) in API 16, which this question was about.