Android :: Drawings Of View.onDraw Not Shown When Canvas Rotated
Mar 7, 2010
I have create a subclass of View and overwritten onDraw() - see some test code below. It draws a line consisting of some points. Before the line is drawn the canvas is rotated and restore after the drawing. The angle by which the canvas is rotated increases by 5 degrees every time onDraw() is called. The view is invalidated about once a second causing the view to be redrawn. Due to the rotated canvas the line drawn looks like a clock hand rotating counter-clockwise. This works - but not always. Sometimes the line is not drawn for one or more seconds, although I know from the log statement that onDraw() was called. Sometimes means: The line may be not shown after 8 seconds, then again after 35 seconds and so on. If the canvas is not rotated the problem does not occur. This also happens when I use a SurfaceView instead of a View. It does not only occur in the simulator but also on my G1 - both using Android 1.6.
CODE:.............
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Mar 11, 2010
I am trying to draw an animation. To do so I have extended View and overridden the onDraw() method. What I would expect is that each time onDraw() is called the canvas would be in the state that I left it in and I could choose to clear it or just draw over parts of it (This is how it worked when I used a SurfaceView) but each time the canvas comes back already cleared. Is there a way that I can not have it cleared? Or maybe save the previous state into a Bitmap so I can just draw that Bitmap and then draw over top of it?
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Mar 27, 2009
Specifically I want to know if one can give me better performance. I want to draw the whole surface myself as I am scrolling a large bitmap. Basically I am trying to figure out how things like ListView / GridView do smooth scrolling (see thumbnails in picture viewer app) and writing custom views (even using surface views) seem to be flicker a lot.
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May 16, 2009
The green plane is shown on the golden-brown surface but when I press a key nothing happens. I want eventually be able to move the plane pressing 4 different keys + another one for shooting but that's easy if I can just get the thing moving in the first place. When I press a key in the emulator, nothing happens at all.
CODE:............................
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Feb 24, 2010
I am using the MapsDemo example for a mapping application where I rotate the map in direction of travel. This works well even without the canvas smoothing in the example.
However, I haven't yet managed to adjust the dispatchTouchEvent code to counter the map rotation effect for the user touches (right now when the map is rotated 90 degrees a user's horizontal sweep will move the map vertically etc). The sample code only offers the teaser:
CODE:..........
And while I am at it - Is it still possible to position the zoom controls separately, so that they do NOT rotate when the map rotates? I read that the getZoomControls() is deprecated.
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Aug 26, 2009
I have a View and that has a canvas. I am rotating the canvas, for rotating a bitmap. But after that, I need to draw one more bitmap on the Canvas and, this should not rotate. The second bitmap has to be static.
I tried with matrix rotation for bitmap. But its not rotating in the specified co-ordinates.
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Sep 9, 2010
I am using SurfaceView to draw my game on the screen of the phone. Basically now I want to be able to draw Android Views on my View, such as a Button or ListView. I am simlpy getting a Canvas and then I draw on that... does anybody know how to draw AndroidViews (Button, ListView.) on my Canvas?
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Mar 6, 2009
Can anyone explain me the difference between View's Canvas and Bitmaps Canvas
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Sep 29, 2010
I have a view that is round and hovering above (-> in z-axis direction coming out of the screen) the main content. When the someone taps the screen I want either the main content to be selected or the view hovering above, when it covers the main view.
So far that works perfectly. I have a round shaped item on a transparent canvas. Meaning you can see everything of the background that is outside of that circle. However, you cannot select it, because it is still the hovering canvas, just with a transparent paint.
Now I'm wondering, to solve this issue, if it is possible to make the view/canvas itself round shaped?
Update
I added an image for better explanation what I try to achieve.
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Sep 29, 2010
How can i draw a view on a canvas by giving the x,y position in the canvas.
For example,
I have custom view myView, which was created by inflating one of my layout.xml file.
Now i want to draw this myView on the canvas at position (x, y).
How can i do that? code...
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Apr 4, 2010
I called canvas.drawBitmap to draw an image, but somehow it's showing up behind/underneath the custom view (or it's background). can someone explain this?
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Jun 3, 2010
I'm new to opengl-es and I wonder how people are able to draw these much detailed OpenGL ES graphics, e.g. on Android OS. It's already hard to draw a single squre, because it's composed of triangles due to the reason that OpenGL ES obviously cannot draw anything else than triangles.
I thought about this approach:
Drawing and rendering an object in Blender.
Export it somehow as array of vertices and an array of colors
Copy this array of vertices into the Java code
Run the code
Or are there approaches to solve such problems in a better way? I do not think that people just "draw" their graphics as array of vertices in the code. I'm sure they draw them anywhere else and import it into the code.
If there is such a solution with Blender, I would be pleased to know how this is solved.
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Jul 19, 2010
I am drawing text in my custom view in android using canvas.drawtext. i need to change back color, and want text right aligned. for example i want to print the text in a 10, 10, 100, 20 rectangle of color yellow and text color red and right aligned. how can i do that ?
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Apr 7, 2010
I have a views on the main class and many other class with an onDraw() method to draw a canvas.
Java:
CODE:.....................
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Jul 7, 2010
My loadMap() method generate a canvas.throwIfRecycled exception when i try to load a new map.
When i start the game, the initial map loads and work fine though,
its only when i try to load a new map that i get the exception ..
How can i "reset" canvas and the bitmap i use to draw into, so i can startover fresh with them ?
here's what i use to create and draw my maps:
CODE:.........
So basicaly once i created and used picDest and canvas, i cannot figure how to reset it all for when i want to load a new map..
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Dec 3, 2009
I'm using a class extends with view. I'm using timer in that class. I'm using onTouchEvent() also. I onTouchEvent() I'm using invalidate(). So it is calling onDraw(). When i use invalidate() in Timer. It is not calling onDraw().
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Apr 19, 2010
I hope this question belongs in the Android Developers and not Android Beginners group but I have a question about ScrollViews. I am currently working with a customized GraphView class and am trying to put it into a ScrollView but it doesn't seem to work. Whenever I run the code, it comes up with a blank screen. I've written the code in XML and also tried to create the ScrollView encapsulating the GraphView programmatically but whenever the code runs, it comes up with just a blank screen and GraphView's onDraw() is never called.Code...
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Aug 13, 2010
I can add children just fine, but I'm never getting my custom onDraw() being called. dispatchDraw() gets called, but that seems to have a different canvas (the one that's within the padding. I need to draw on the whole layout area). Is there some flag that needs to get set to get onDraw() called for the layout?
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Dec 11, 2009
I have a ListView with an adapter attached. In the individual list items are placed views with widgets that continually update themselves within the list. Everything works well except for this case: Touch the list and start scrolling it just before the longTouch event would be thrown. Then lift your finger from the ListView. At this point the widget views in the ListView no longer receive onDraw events in response to the invalidate calls that continue to be made on the ListView. It is like the ListView starting blocking the invalidate calls during the scroll and forgot to re-allow them when the scrolling stopped. If I touch and scroll with out holding or scroll with a fling this does not happen. The ListView will start allowing the onDraw events back through if you touch anywhere in the list. Any ideas on how to help the ListView not block those onDraw calls?
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Apr 8, 2009
We came across a strange behavior. The clip rect of our custom view is getting reset to its entire visible region, if we change the value of another view.
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Apr 21, 2010
I'm trying to modify the SurfaceView I use for doing a camera preview in order to display an overlaying square. However, the onDraw method of the extended SurfaceView is never called.
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May 9, 2010
I want to show an arrow that indicates the direction towards a goal, using the orientation sensor and current GPS position. Everything works well, except that I want to rotate the arrow image in my ImageView.
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Nov 24, 2010
I need to put some text over an imageview.
CODE:..........
But this doesnt displays the text only the picture. And also I have to rotated this text. Is this even possible with TextView?
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Jun 23, 2012
I have a simple draw application on Canvas. User should be able to draw with a chosen color. On MotionEvent.ACTION_UP, invalidate() is called. Now it redraws previously drawn lines with the current color ( Redrawing the entire drawing with the current color). I do not want to change the color of previously drawn lines. I am not sure what is missing. Can I make it redraw only newly drawn lines?
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Jun 8, 2009
When camera is launched in portrait mode, the viewfinder screen is 90 degrees rotated and stretched out. I read couple of places that this is a known bug with sdk1 but i am still finding this problem with cupcake. Has anyone having any idea is this issue is fixed in cupcake or in donut? any clues how to move ahead. setOrientation and changing the preview size didn't help. Even I read somewhere Surface flinger class needs change: http://groups.google.com/group/android-framework/browse_thread/thread...
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Mar 14, 2010
I am having trouble finding information related to which i should choose, OpenGL ES 1.1 or 2.0 for 2D graphics.
OpenGL ES 1.1 on Android is a bit limited to my knowledge, and based purely on sprite count the only useful renderer is draw_texture() (as far as i know). However, that does not have rotation and rotation is very important to me.
Now with the NDK adding support for OpenGL ES 2.0, i am trying to figure out if there is anything that preforms as well as draw_texture(), but can handle rotation.
Anyone have any information on if 2.0?
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Oct 5, 2010
I would like to display some UI Elements on a android xml layout file. I try to make an application, where two players can sit at each end of the mobile device, and play against each other.
So need to show some Button 180 degrees rotateted.
Is this possible? I tried android:gravity, but this did not work.
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Jun 11, 2009
I am using the code from ApiDemo Camera Preview and it runs fine on my Gphone but the preview is rotated and stretched.
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Jun 15, 2010
I would like to know as to what will happen to the thread which has been created by an activity and the device is rotated. I have observed that the onDestroy method is called when this happens. Will the thread be killed too?If the thread is not killed, how can I reassociate the thread with the activity as a new instance of the activity is created on rotation.
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Jun 26, 2009
I am getting a crash intermittently when my Activity starts up either initially or when the screen gets rotated I get several log messages which I have been unable to get any insight from: timeout expired mFreezeDisplay=1 mFreezeCount=0 App freeze timeout expired Force clearing freeze then lots of: Lock_layer timed out (is the CPU pegged?) Key dispatching timed out then I get ANR annotation: keyDispatchingTimedOut the trace has alot of sending signal 3 to alot of PIDs
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