Android - 仅顺时针旋转视图180度

Question

I want to rotate a button only in one direction 180 degrees depending on a boolean flag. So when the flag is active the button should have a rotation of 180 and otherwise 0. This works perfectly:

button.animate().rotation(active ? 180 : 0).setDuration(250).start();

But the button is not rotating always in the same direction cause for example if the target rotation is 0 he will rotate counterclockwise.

So my question is how can I achieve the 180 rotation animation always be clockwise?

Edit:

So one important note is that the code could be called multiple times. So if I use rotateBy (from the answers below) it would rotate althought if it was active before. Sorry I forgot to mention that. So if the flag is active it must be rotation % 180 == 0 otherwise rotation % 360 == 0 or rotation == 0

Answer 1

I believe it's because the view will turn clockwise when your end degree is larger than your starting degree and counterclockwise when it's reversed. You could try getting your current rotationX value and adding 180 to it.

EDIT:

view.rate_button.animate()
    .rotationBy(view.rate_button.rotationX + rotationValue)
    .setDuration(250)
    .withStartAction { active = true }
    .withEndAction { active = false }
    .start()

EDIT 2:

behaviorSubject.subscribe({
    if (active && view.rate_button.rotationX == 0f) {
        // Active state is true but the button is not rotated to 180
        // degrees like we need so set the rotation value to 180 so we 
        // can still increment.
        rotateButton(180f)
    }
    else if (active && view.rate_button.rotationX == 180f) {
        // Active state is true and the button is rotated to 180
        // degrees like we need set the rotation value to -180
        // basically canceling out any rotation.
        rotateButton(-180f)
    }
    else if (!active && view.rate_button.rotationX == 0f) {
        // Active state is false and the button is rotated to 0
        // degrees like we need set the rotation value to 0
        // basically canceling out any rotation.
        rotateButton(0f)
    }
    else if (!active && view.rate_button.rotationX == 180f) {
        // Active state is false but the button is not rotated 
        // to 0 degrees like we need set the rotation value to 180
        // so we can still increment.
        rotateButton(180f)
    }
    else {}
})

private fun rotateButton(rotationValue: Float) {
    button.animate()
        .rotationBy(button.rotationX + rotationValue)
        .setDuration(250)
        .start()
}

For simplicity I'm still using an onclick event to fire off the behaviorSubject.onNext event but any action/event would work.

Answer 2

而不是旋转（float）使用rotationBy（float）方法。

button.animate().rotationBy(active ? 180 : 0).setDuration(250).start();