Android image scale animation relative to center p

问题:

I have an ImageView and I do a simple scale animation to it. Very standard code.

My scale_up.xml:

<set xmlns:android="http://schemas.android.com/apk/res/android">
    <scale android:fromXScale="1"
           android:fromYScale="1"
           android:toXScale="1.2"
           android:toYScale="1.2"
           android:duration="175"/>
</set>

My animation code:

Animation a = AnimationUtils.loadAnimation(this, R.anim.scale_up);
((ImageView) findViewById(R.id.circle_image)).startAnimation(a);

The problem:

When the image scales it doesn't scale from the center, but from the top left corner. In other word, the scaled verion of the image doesn't have the same point as center, but it has the same top-left point. Here's a link that explains what I mean. The first image is how the animation scales, and the second image is how I want it to scale. It should keep the center point the same. I have tried setting up gravity on the image, on the container, aligning left or right, it always scales the same. I'm using RelativeLayout for the main screen and ImageView is located into another RelativeLayout, but I tried other layouts, no change.

回答1:

Forget the additional translation, set android:pivotX, android:pivotY to half the width and height and it will scale from the center of the image.

回答2:

50% is center of animated view.

50%p is center of parent

<scale
    android:fromXScale="1.0"
    android:toXScale="1.2"
    android:fromYScale="1.0"
    android:toYScale="1.2"
    android:pivotX="50%p"
    android:pivotY="50%p"
    android:duration="175"/>

回答3:

The answer provided by @stevanveltema and @JiangQi are perfect but if you want scaling using code, then you can use my answer.

// first 0f, 1f mean scaling from X-axis to X-axis, meaning scaling from 0-100%
// first 0f, 1f mean scaling from Y-axis to Y-axis, meaning scaling from 0-100%
// The two 0.5f mean animation will start from 50% of X-axis & 50% of Y-axis, i.e. from center

ScaleAnimation fade_in =  new ScaleAnimation(0f, 1f, 0f, 1f, Animation.RELATIVE_TO_SELF, 0.5f, Animation.RELATIVE_TO_SELF, 0.5f);
fade_in.setDuration(1000);     // animation duration in milliseconds
fade_in.setFillAfter(true);    // If fillAfter is true, the transformation that this animation performed will persist when it is finished.
view.startAnimation(fade_in);

回答4:

You can use the translate animation in your set to offset that. You'll probably need to tweak the toXDelta and toYDelta values to get it right so it keeps the image centered.

<set xmlns:android="http://schemas.android.com/apk/res/android">
    <scale android:fromXScale="1"
        android:fromYScale="1"
        android:toXScale="1.2"
        android:toYScale="1.2"
        android:duration="175"/>
    <translate
        android:fromXDelta="0"
        android:fromYDelta="0"
        android:toXDelta="-20%"
        android:toYDelta="-20%"
        android:duration="175"/>
</set>