Develop Reference

Android video-like animation, how to create?

In this mock up, see the screen where it said "Decrease Traffic", the traffic light pops up from below.
https://dribbble.com/shots/2106573-Intro-App-Interaction
I'm wondering how to create that effect on Android, if possible, any library to do that. Thanks

you can achieve this with Android Property Animations
in your example it seems to be a scale animation from 0 to 1 in x and y direction.
you can also combine different animations to get such or other effects.

My guess is that these kind of animation are to develop with a 3rd party program, and are not done by Android itself.
This way you have a ready-to-instantiate file (.gif maybe?) that you just call when the view pager is switched.
Looking also to the other animations in the example (look # "Meet New Friends", how every circle pops by himself) I think this was the used approach in your example-link.
If you are anyway looking for something that would look like what is done there, I'd suggest you start playing around Animator objects (and its subclasses like Value/ObjectAnimator) to animate the view you want.
This can be done also via XML files, describing the animation you need.
An important role in this do-it-yourself animation is played by Interpolators , who give you the chance to further customize the animation in an easier way (take a look at OvershootInterpolator, which lets your animation go a bit after the destination value you set, just to turn back later, giving you a "blob" effect. This might give a better idea what I'm meaning)

How to deal with overlapping RotateAnimation-s on Android?

I am using RotateAnimation to animate pointing arrow that updates its position when of user updates destination point or current device position changes. I'm using interpolator.accelerate_decelerate to make animation look more smooth and "physical".
Everything goes fine until another update arrives when current animation is still processing, for example, when user changes destination while pointing arrow is still rotating. When such happens, the arrow makes a sharp bounce which looks ugly, and I'm trying to avoid this. I tried to implement a queue to make every next animation wait until previous ends and it looks nice, but behavior became quite illogical.
So my questions are following:
1) is there some way to make animated transitions more smooth in the cases when animations start one by one and overlap each other?
2) is there a way to stop animation that is currently processing and get intermediate position of an object?--if I decide to stop animation before its end and use current position as starting point for next animation.

ok so the easiest is to create a custom Animation similar to RotateAnimation and saving the current rotation angle in applyTransformation, this angle can be then used as a start angle for next Animation thus avoiding the "jumps"

A custom class extending ImageView that performs animation based on angular movement of dipole in magnetic field:
https://stackoverflow.com/a/22738030/3459206

Smooth animation transition logic in Android OpenGL

I have an Android app developed using openGL and LibGDX.
Right now I do not know the strategy on how to code smooth transitions among a set of animations.
Example:
We have a cat actor.
Its animation consists of a set of key frames paired with transform matrix.
We have 5 preset animations for this cat:
idle, walk left, walk right, jump and lie down.
How can we transition from lets say
walk right => lie down
walk right => walk left
while the walk right animation is playing half way?
Right now once an animation starts, it needs to be played for 1 full cycle until the end.
This is so that the cat can move back into its neutral position.
Thus it can play the next animation which starts from a neutral position.
The final result is unnatural and jerky.
What approach should I use to tackle this problem?

Just starting the next Animation even when the previous one isn't finished is the Standard way. It looks good, do not wait for the first Animation to finish.
If you still think it looks unnatural. Then you must create a very fast "transition frame" between animations that makes it look more natural. Not worth the effort if you ask me, just try it the first way :)

android - Slide ListView with setX, setPadding, or tween animation?

Without going into too much detail, I want to be able to 'slide' elements in a ListView similar to the 'slide to archive' feature in GMail. I'm fine with the onTouchListener and all that, my question is regarding the slide animation.
The first two things that come to mind are..
view.setPadding(slideOffset, 0, 0, 0);
and..
view.setX(slideOffset);
The former is very buttery, even on the emulator.
The latter is a bit janky on my Galaxy Nexus.
My questions:
* Regardless of what I've tried, what's the correct way to do this?
Why is setX less smooth than setPadding?
Does one approach conform to Android best practices more than the other?
Are tweened translation animations an option? If so, can you provide a brief example to point me in the right direction please?
Edit:
To be clear, I am attaching an image of the effect I am trying to emulate.

I'm pretty sure the setX() is slower because it affects its parents. When changing the X of a view, it calls the onLayout/onMeasure of the parent every time you update the value. That's because the X value of the child may cause other items on the parent to move, therefor the parent needs to redraw itself.
You can test this easily by extending the ViewGroup and writing to the log on those methods. Then, you can use both approaches, padding vs. setX, and see what happens.
Are you trying to animate the item? Or do you want the user to move it like on Gmail? You can use the ObjectAnimator to handle the "X" value of your item. Combined with a "hardware layer" for your item, it will create a smoother experience. You can find more details about how to do that here: http://developer.android.com/guide/topics/graphics/hardware-accel.html

Yeah, if you're targeting higher APIs, ViewPropertyAnimator is probably a great solution. If you have to support lower APIs, my thought process for implementation would be (and I haven't implemented this myself personally, but this should be good for performance) to:
In your touch handler, once you've determined that the user is "sliding", set the View's visibility to INVISIBLE, and store the drawing cache into a separate bitmap (Bitmap bmp = myView.getDrawingCache();)
Draw that bitmap in the same place as the view, and use the Canvas translate methods to shift the position according to the x-position of the user's touch point.
After the user lets go, translate back (preferably smoothly with an animation), recycle the bitmap, and set the view back to VISIBLE.

Check out the 3 devBytes posted on AndroidDev:
https://www.youtube.com/watch?v=8MIfSxgsHIs&list=PLWz5rJ2EKKc_XOgcRukSoKKjewFJZrKV0&index=12
https://www.youtube.com/watch?v=NewCSg2JKLk&list=PLWz5rJ2EKKc_XOgcRukSoKKjewFJZrKV0&index=11
https://www.youtube.com/watch?v=NewCSg2JKLk&list=PLWz5rJ2EKKc_XOgcRukSoKKjewFJZrKV0&index=11
https://www.youtube.com/watch?v=YCHNAi9kJI4&list=PLWz5rJ2EKKc_XOgcRukSoKKjewFJZrKV0&index=4
https://www.youtube.com/watch?v=PeuVuoa13S8&list=PLWz5rJ2EKKc_XOgcRukSoKKjewFJZrKV0&index=3

Whats the best way to do character animations with Box2D?

I am developing a 2D, underwater, action-RPG for Android, using Box2D as the physics engine, mainly for collision detection, collision response and movement of in-game characters within an environment comprised of walls, rocks, and other creatures.
I have tried two different approaches for implementing character animations using Box2D, and have found issues with both. As I'm new to Box2D and physics engines, I would appreciate a recommendation on how these things should best be done.
An example of an animation I am trying to do is as follows:
A fish wants to attack another fish, so does the following:
1) Move towards target at speed
2) Take a bite out of target creature
3) Turn and flee, back to where the attack began
4) Turn back to face the target, ready for another attack
The two approaches I've tried are:
A) Apply a force to the attacker (using body.applyForce() ) to move it towards the target, then another force to move it back again, after the collision
Problems:
* Frequently the attacker hits the target and bounces off and goes hurtling back at great speed, and bounces off walls, everywhere. The speed is pretty random, depending on where it impacts the target, the mass of the target, etc. It breaks the animation and looks terrible.
* It's very hard to figure out what forces should be applied to the attacker and when, to simulate a particular animation in a physics world so it looks realistic
B) Directly set the position of the attacker (using body.setTransform() ) to move the attacker to the correct position, as it moves forwards each step, then moves back again.
Problems:
* Directly setting the position allows the attacker to ignore collisions with walls and other creatures, so getting stuck in a wall is common
* If the player is attacking, I update the world origin as the player moves, to keep the player mid-screen. This works well, except when I start an animation, as I don't want the screen to follow the animation, but only the movement component of the existing velocity, which I don't know, as I'm overriding the Box2D forces/velocities when I set the position. It's possible to do this I'm sure, but difficult - maybe I'm missing something obvious.
Should I be monitoring the collisions? Overriding the collision response?? Something else?
So, how would you recommend I approach this problem?

I'm only used to work with Farseer, but Farseer is a pretty direct port from Box2D, so I hope this answer is still helpful.
Next to applying force and teleporting you can also set the linear movement speed of a body. This way you can have the fish move towards the player without applying force. You should capture the collision events from the fish body and compare in each event if the fish has hit the player, then set false/NoCollision in the collision event with the player so that it doesn't bounce of. Now set the fish body to ignore any collisions with the player body and use a fixed joint to stick the fish to the player. You can now play your bite animation.
After the bite animation you want to disengage the fish. Start your flee animation, remove the joint and teleport the fish to the edge of the player body (so that it's not colliding with it). After that re-enable collisions between the fish and the player body and send the fish away from the player (either by setting linear movement speed again, or for a nice bounce effect via force.