fengmin Yes, it will not work if one of them is set to <None>. To achieve what you want, specify the mix duration when you set or add that animation to the AnimationState track. To specify the mix duration of a particular animation, use the TrackEntry object. For example, it can be written like this:
TrackEntry entry = state.setAnimation(0, "c00000", true);
entry.mixDuration = 0.2;
This way there will be 0.2 seconds of mix before the transition to c00000, no matter what the previous animation playing on track 0 was. General information about mixes is explained in the Spine runtimes guide:
https://esotericsoftware.com/spine-applying-animations-zh#%E6%B7%B7%E5%90%88%E6%97%B6%E9%97%B4
