i am new to android and cannot find any suitable way to make a canvas scrollable. I have searched a lot but no one's giving a complete overview of what is to be done actually. Just vague ideas & incomplete code examples. Any help would be appreciated. I have extended the from scrollview and have drawn a png image on canvas which is greater than the screen size. Scrollbar do show up but then fade away & no scrolling. what am i missing?
If you mean you have a custom view with a Canvas you're drawing to, then you have to implement scrolling yourself. But fear not! There is a nice things called GestureDetector and Scroller already made for you to make it easy.
You just need to listen to its scrolling/fling events and update xOffset value with which you gonna draw on your Canvas.
Basically in your draw(Canvas) method you don't just call
drawSomething(x, y)
but
drawSomething(x - offset, y)
If I'm describing the problem you have and it's still unclear - let me know, I can expand further.
Related
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
I'm trying to create an interactive accordian/concertina/folding animation so that a view folds/unfolds on itself when interacted with - in the same way flipboard folds the view, but both sides fold
The way I thought I could do it was to override the onDraw method, somehow duplicate the canvas or the information on the canvas, then draw the first half of the canvas rotated one way, then draw the other half of the canvas rotated the other way so that they meet in the middle, however I can't seem to grab the information from the canvas! Is it possible to grab a bitmap/snapshot from a canvas?
The only other way I think it's possible to achieve this kind of animation is with OpenGL.
Any help are greatly appreciated.
EDIT heres a good example of what i want to achieve http://www.nytimes.com/interactive/2008/03/28/arts/20080330_FOLD_IN_FEATURE.html
check this archive to acheive fold animation
code: http://developer.android.com/shareables/devbytes/FoldingLayout.zip
modifies it to make it work for lower version up till API level11
I've got some problem. I have an image drawn using canvas, and I would like to animate it. I would like to do something like TranslateAnimation, but TranslateAnimation works only with views, and my image is not a view. What can I do?
Personally I haven't worked with Android canvas, but I am fairly certain that what you need to do is this:
Draw your shape on the canvas
Wait for a couple of miliseconds
Clear the canvas
Redraw shape to next immediate position
and repeat this until the final position is reached.
From my little knowledge the canvas is more similar to a piece of paper than to a flash animation. You need to draw, clear, recalculate, redraw. I highly recommend reading some more on the topic. Firstly, I would start with the android canvas reference: http://developer.android.com/reference/android/graphics/Canvas.html
and then try some tutorials like canvas frame by frame tutorial for android : http://developingthedream.blogspot.ro/2011/01/android-canvas-frame-by-frame-animation.html
And also I highly recommend looking up things on google first before posting a question on stack. There is a good chance, especially if you are a beginner, to find existing tutorials with everything you need and more. Good luck learning.
I have a background image that I would like to simply scroll (while looping) right to left. What is the best way to go about doing this? Will I need to use an external library? Are there certain methods built into android already to accomplish this? Is all this accomplished in the doDraw() method?
Eventually I would like the canvas to also draw a stationary Bitmap ontop of that. I think that will be easy if I just use the canvas.drawBitmap() function.
Easy example including X offset
http://android10.org/index.php/articlesuserinterface/256-live-wallpaper-example
and canvas
I implemented a custom android SurfaceView class which draw (onDraw method) something often bigger than the available device width and height. When the user toutch the screen and move it's finger I need to implement a kind of picture movement with a speed and direction matching the speed and direction given by the user. That part I'm able to do it within onTouchEvent method. But here is my question: now I also want the speed to decelerate progressivly. I think this probably have to be coded with DecelerateInterpolator... Is there some samples or demos somewhere involving a SurfaceView, onTouchEvent and DecelerateInterpolator... ?
I was thinking of a too complicated way to address the problem. Finally found a way to solve my problem here: Smooth scrolling in Android The OnGestureListener simplify all gestures management.