I want to put some graphical shapes (e.g., a character, some moving objects, etc.) in a big view, and being able to touch them.
What should I use ?
- A drawable object is simple to draw but it can't be attached to a touch listener. How can I detect a click in the bounds of my shape ?
- With views, I can use a touch listener, but is it a good idea to use views to draw graphics in a game ? Aren't they better for forms ? Also, I want to put those shapes anywhere on the screen (absolute position). I cannot find a way to do this with views.
Thank a lot.
It sounds like you would want to draw the objects within a single view (your drawable object method) and then use a touch listener on that encompassing view. In that listener, you would compare the touch position to the positions/bounds of the objects you are drawing - and if the touch would qualify as being 'on' an interactive object, you would then handle it accordingly.
Related
I've recently started building my second android app and I've hit a wall. What I want to know in general is this. In almost all other programming languages that I've used there is a simple way of drawing arbitrarily on screen. Usually there is some sort of Scene or Canvas type class and another GraphicObject type class. So If, say, I want to draw a car, I create a class that descends from GraphicObject and define they it draws itself and then add an instantiation of the Car class (the object) to the Scene. If I want a second car, you just instantiate another and put it wherever you like, by setting some kind of coordinate function. If this is a program where what is drawn depends on user input, everything must be done programatically and hence it does not depend on anything other than the code written.
How do you achieve this in Android? As far as I can muster the only object which you can define the way it is drawn is a View. However I have not been able to simply take my custom view (that draws a rectangle in my case) and instantiate two of them a put them in the screen where I want them, and do this in a programtic simple way....
Thank you for any advice.
Well if I want to draw lets say 10 rectangles then I wont instantiate my custom View 10 times. Instead I will add logic in my custom View to be able to draw 10 or more rectangles. Anyway if you want to draw again what was drawn in a View then you can call setDrawingCacheEnabled(true); on your View and then call getDrawingCache() to get Bitmap to draw it somewhere else.
Its almost same in android also,
All the widgets are inherited from class View, by extending this class you can actually create whatever you want limiting by only yours imagination, you have access to canvas here, use it along with touch controls exposed from class itself to override all the behaviours you want as per your need,.
http://developer.android.com/reference/android/view/View.html
http://developer.android.com/reference/android/graphics/Canvas.html
My idea is to have two surfaceViews. One surfaceView which will hold an image (say ImageSurgaceView) and second surface that lie on top of the first one which holds the annotations (say AnnotationSurfaceView) like circle, rectangle etc. Now I have to map these surface views such that the height, width are same and moreover, both the surface view should move on drag i.e share the touch events. To be precise, when I move the image up the annotations should also move up.
Now, I am not sure if this is possible in android. Can any one tell or share some info on this. I don't have any implementation idea to this and hence I don't have any specific code. Moreover, I couldn't find anything similar.
Thanks for helping.
Yes, this is possible. You can add both SurfaceViews as children of a FrameLayout. You will also want to call setZOrderMediaOverlay on one or both of your SufaceViews in order to specify how they are layered.
Furthermore, this could be a graphic intensive algorithm you are describing. Consider adding the AndroidManifest.xml application attribute android:hardwareAccelerated="true".
Finally, just set up a custom OnTouchListener to handle drag events. Use MotionEvent.getRawX() and MotionEvent.getRawY() to get the touch point, and use this to manipulate the canvases.
I've been working on this for a while but can't find anything that exactly addresses my question (at least not something easy to understand).
I have a main layout XML file where I define various layout objects like a Button or a TextView (and I know I can add SurfaceView, View, and view and other things too). I want to draw a shape (in my case it's an arc) in just one of these objects so it doesn't take up the whole screen and so I can position it relative to other things.
(In my case it will ultimately re-draw the arc kind of like a circle with a gap in a different position every time I call a method depending on a value I pass to the method, but that's separate from my basic question.)
I know the answer will have something to do with a canvas, an onDraw method, maybe Paint, probably a view. I have been able to draw a circle from a custom View object by setting the main java file's layout as that View (as opposed to R.layouts.main), but that takes up the whole screen, and I'm unsure how I might be able to have that dynamically draw with modifications.
A really clear explanation or better yet an actual example would just be awesome.
As i see it u need to draw a specific shape on widget and not on complete screen. Try using layer List.
you can refer this link for sample Link
I want to be able to dynamically place image(s) over another image in my app.
Consider the first image as background and the other images to be on top level, I will also need to move those top level images (change their x and y on the screen) by code too.
Imagine, for example, a sea in which the user places fish and sea animals, then those sea animals start to move here and there on the screen: it will be like that.
How can I do this? If you don't know but remember any simple program or demo that does that, it will be also very welcome!
Thank you!
There is, of course, more than one way to do this, but I would say that the best way to do it would be to create a custom View (class that derives from View) and have this handle your bitmap drawing and all of your touch events.
There's a lot of code to write for loading the Bitmaps and keeping track of all of their positions (and then drawing them to the canvas in onDraw), but if you start really small by just allowing one image to be drawn and dragged around the screen, you can build on that and keep your code organized.
You would need to override onDraw(Canvas) and onTouchEvent(MotionEvent) in your custom View. You'll load your bitmaps with BitmapFactory (decodeResource method if you're including your images as resources in your project) and you'll need to remember to call recycle on your bitmaps when you're no longer using them.
In onDraw, you draw your bitmaps to the canvas at a specific location using Canvas.drawBitmap. There are two overloads of this method you can choose from, one that takes the top and left coordinates of the bitmap as floats (and therefore performs no scaling or stretching) and one that takes a destination and source rectangle to perform scaling, stretching and placement.
I always use the latter as it gives me finer tuned control. If you choose this route, you'll want to keep two Rect instances and a Bitmap instance for each image being drawn, update them in the touch events and draw them to the canvas in the draw event.
When something changes inside your view (as in the case of a touch event), call invalidate() method and the framework will know to redraw everything which triggers your onDraw method.
I have a custom view (extends View) that is going to be a game board. What I'd like to do now is create an object (well, a bunch of them, but I can start with one) at a specific location on the board and then have the user be able to move it around by dragging it. I have the board view down, but am at a loss on how to code up the "pieces." Thanks for any help and/or pointing to the right place here.
Some pointers:
You will need to capture the user's touch 'n drag. Unfortunately you can't use a GestureDetector.SimpleOnGestureListener for this (it would see it as a scroll), so you'll have to do this in your view's onTouchEvent. This is a little tricky - refer to the SimpleOnGestureListener source code for ideas on how best to do this.
As you update the location of the object call invalidate() on the view to trigger the re-draw
In onDraw() do the background and then draw your object on top
If you are just doing the one object at once this should be sufficient. If there's more to it that this you may have to graduate to a SurfaceView and a separate thread - but don't go there until you need to.