Develop Reference

How to do a scroll animation in Android?

I'm new to Android programming. I'm working on an app that requires some form of animation. Please take a look at
I want an animation where a scroll rolls down at the top with this text in it as soon as this activity starts & rolls up when the connect button is pressed. I have no clue where or how to begin with the animation. Any kind of links to tutorials or posts on StackOverflow will be of much help.
Thank you for your time!

Since your question is really really broad, I'll give you a broad answer as well.
I think by "scrolling animation" you mean an animation in which a black (or some other color) area slowly covers up/reveals the screen. I don't know why would this look cool, but whatever.
Step 1
Create an animation XML file. In this file, you would specify that the view should translate downwards by x pixels where x is the height of the screen. And create another animation file. This time, specify that it should translate upwards.
If you need help creating XML view animations, have a look here
Now you have two animations - move upwards and downwards.
Step 2
Okay, now you should create a custom view. You can start by doing this:
public class ScrollingView extends View {
}
And implement all the required constructors.
Override onDraw like this:
cover the whole view with black or some other color
draw the scroll at the top of the view. The scroll should be an image like this one:
If you don't like using an image, you can draw it yourself, using code!
You can get help on this here
Step 3
In onCreate of your activity, create a ScrollingView. This view should be as wide as the screen and as high as the screen. Position the view at (0, 0) and bring it to front so that it covers up the whole screen.
Step 4
Next, apply the animation you created in step 1 to the scrolling view.

Animated reveal for 14+ Android

I'm tackling the task of an overlaying drawable over a view that animates the drawing of a checkmark as in the following video https://vid.me/MsQj
I don't have a preferred method for doing this but it's just not coming out the way I wanted it to, I tried:
Two views, each with on side of the checkmark to be revealed with an animation, however I'm stuck at the "revealed with an animation" since I can't use the circular reveal on -21
Frame by frame animation, this is the easiest but I'd hate to have 60 images for this stupid animation if it can be done programmatically
Drawing on a custom view canvas
My question would be, is there anything that can make this easier on me, or do I have to tackle it head first and just get on with it

You could create a custom View class which contains two lines defined by ShapeDrawables, one for each leg of the tick. Expose the lengths of these two lines as properties of the class, and then use Property Animation to animate the lengths of the lines.
Property Animation is flexible enough to handle pretty complex timing and sequencing of various properties. In this particular case you would probably want to use an AnimatorSet to sequence the two line animations so the second starts once the first has finished.

I ended up developing a custom View thanks to #SoundConception suggestion and finding out about ObjectAnimator which are very powerful in Android. In essence what goes on is we set a width for the first and second line that make the checkmark and using the animator change the value of those properties from 0 to the desired one.
On the setter for the property, we invalidate the View to redraw it with the new value and with a little tweaking I made a nice View that while its currently only working for my specific layout (ie it needs some more work on the offset calculation) it's able to draw an animated checkmark with some stuff that is customizable.
Precisely, you can set the line width, the color, the length and the animation time. And touching the java file, you can change the interpolator and all the rest of the stuff.
Hopefully the code, while not really commented serves as a basis for someone trying something similar.
For example the following code would generate something like this video, although not really because I was testing opacity and thinner lines, but you get my drift.
<coop.devtopia.CheckmarkView
android:layout_width="250dp"
android:layout_height="250dp"
android:layout_centerInParent="true"
android:id="#+id/view"
app:first_leg_length="50"
app:second_leg_length="100"
app:total_duration="1500"
app:stroke_width="20"
app:stroke_color="#22000000"/>
Repository
Update 4/2/15
I've played with this a little further and added dynamic offset calculation (fancy way of saying centering) to the tick, meaning we can generate big checkmarks, small checkmarks, skinny or thick, reversed or straight and they will be centered in the view. Can't guarantee the same for checkmarks bigger than the container, they will likely be cropped.
Here are a few of the checkmarks generated for this demonstration, of course the animate as if drawn and the effect can be very pleasing and resource friendly. This turn out to be a pretty interesting subject after all.

What options are there for arranging custom ImageViews

I have recently completed a simple drag and drop shapes game. It had the user drag a shape (ImageView) to another "empty place holder" ImageView.
I now want to make this a little more advanced, instead of dragging a simple shape, I want to make a puzzle of various non-orthogonal shapes, for example breaking a circle into 5 different pieces. What I'm having a problem with right now is how to design the layout. I do not know how to make a truly "custom" shaped ImageView, as far as I can find from my research it's not possible. So my idea for now is to overlap a number of square ImageViews, each of which will have only a subset of an image and the rest transparent. Thus the final output will look like it's a number of custom shaped ImageViews.
Example:
+ + +
Because only the internal sections are "visible" and the rest of the circle is transparent, when all of these pieces are placed in the same spot on the screen, the final image will look like:
I haven't tried this yet... but I foresee at least one problem. When I go to drag the pieces over to this puzzle, they will all "snap" into place when dragged to the same place. Because in reality all I really have here is a picture of a circle inside a ImageView which has some invisible rectangular boundary around it.
Hopefully this situation is clear. Now my questions:
Is it possible to have truly custom shaped ImageViews instead of my idea of overlapping images?
If what I'm thinking is the best way to handle this puzzle idea, then what property can be changed such that the "drop" action does not happen at the same place for all of these puzzle pieces? If I wanted to "drop" the pizza shaped piece, I'd like it to only snap into place when it go close to the top left of the circle.
Note: I am new to Android programming, and somewhat new to Java/XML as well, it’s very likely I’m overlooking something, so please feel free to suggest other approaches as you see fit.

Not really. Overlapping views is generally the way it's done. You could also use one View and override the drawing action yourself (multiple bitmaps drawn at relative locations within the View), but that would make the drag-drop aspect significantly harder.
If the Views are all the same size, with the visible portions in the correct relative placement in each, they should snap together correctly. This is because the snap is (I believe) based on the position of the upper-left corner of the View. If the pizza-shaped piece's visible portion is correct with regards to that, it should snap in at exactly the right spot.

So you have certain places you want to accept the drops, and I'm assuming you know their coordinates, say (d_x,d_y).
Then why not simply monitor the coordinate of the center (p_x,p_y) of image view of the piece you are dragging, say the "pizza" piece, and when the distance between the the piece and drop point is within an acceptable amount accept the drop.
But if you are asking if there is some way to make non-rectangular image views I don't believe that is possible.
However I don't think it is necessary in your case, because I believe even if you want them to drag the piece precisely into place you can calculate the coordinates where the draggable rectangle needs to go with knowledge of the shape of the piece and the assumption that the rectangle wraps the piece.

Rotated (not animated) views in XML pre-honeycomb?

Is it possible to rotate views in XML with APIs previous to Honeycomb - maybe with the support package? Or is the only way to create a custom class, like described here Vertical (rotated) label in Android
Edit: What I need is a statically rotated view (specifically a TextView, but I guess it's enough to know how to do it with a View). Starting with honeycomb there's a rotation attribute which can be used in XML. I need something like that.
The only thing I have found until now is use an animation with duration 0 but this still moves a bit at start and I don't want that. I tried setting the views invisible and attaching a listener to the animation which makes them visible on animation finished callback, but that made strange results... that changed the position of the views, for some reason.

The best way is with the custom subclass implementation that you linked to, where you can rotate the canvas and resize the view appropriately. This ensures that the view bounds are also set to match the text that is drawn.
The only method of transforming views externally prior to HC is the animation framework, and applying an Animation to the view with a duration of 0 and fillAfter set to true will work, but you may notice flickering on some devices as often the view will render normally on its first frame and then animated to its final position from that point onward. You can work around this by hiding the view and displaying it a bit late...but you can see how hacks are starting to stack up.
In addition, doing an Animation prior to HC will not transform the view bounds themselves, so you won't be able to neatly pack other views around this one because its position from a layout perspective will still be the rectangle calculated for the horizontal (non-rotated) text.
The simple subclass is definitely the preferred method.
HTH

Is it possible to rotate views in XML with APIs previous to Honeycomb
There is RotateAnimation. However, depending on what you are trying to accomplish, that may not meet your needs.

How to animate views?

I'm working on a game that in some ways is similar to Tetris (imagine a 2D array of colored squares that sometimes move around)
I am trying to animate the individual squares so they will smoothly slide down from coordinate to the next. Since I wanted to use Android's built-in tweening feature, the animation has to apply to the whole View (rather than parts of it). This doesn't work well for me because I only want some of the colored squares to slide down, and the rest of them to stay still.
The (theoretical) solution I came up with to resolve this is to make 2 Views, layered directly on top of each other. The top view is for animating squares when they need to move, and the bottom layer is for the static squares. The animation-layer is transparent until I am ready to animate something. I then simply turn on the colored square in the animation-layer, tween it to the new location, and turn it back off when done. In the same time span, the static-layer just turns squares on and off at the right time to make the whole thing look seamless to the end user.
The proposed solution is just a theory, since I haven't been able to make it work correctly yet. Since I have been having trouble, I was wondering if this is even the best way to solve the problem? Perhaps there is a more elegant solution that I am over looking? Anyone know of a better way?

If you just want to animate a single element check out the namespace android.view.animation.Animation. You can also use Drawable shapes and draw them directly. Finally, if you want a simulation then you will have to look into threading. Basically you will create a timer to update the canvas for you based on an interval. There are some other view canvases you can use as well like the GLView canvas.