Android :: How Does ImageView Just Redraw Part Of Its Content When Invalidate(Rect) Is Called?
Nov 8, 2009
I am new to Android development, just reading docs and trying the APIs. I am quit confused how ImageView managed to draw just a part of its content after an invalidate(Rect) invocation.
I've checked ImageView.java, found no other drawing method except onDraw(Canvas), but onDraw(Canvas) only cut the drawable only if it is beyound the view's visible boundary. I also read the implementation of View.invalidate(Rect), I think the key of this function is calling to mParent.invalidateChild(this, r);
However, I think the parent view doesn't know how to draw the child in the given Rect, it finally has to call some method of it child to paint out. Has anybody investigated this part of codes? Would you please give me some guide?
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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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Aug 14, 2009
I have a custom view, that overrides the onDraw() method. For better performance I want to redraw only a small part of Canvas in onDraw().
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Dec 23, 2009
What's the functional difference between these list view methods: invalidate() and invalidate Views() ? Which one is faster to refresh a list view?
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Jan 8, 2010
I need to create 3 things:
Content Provider
Service
Application
I'm wondering if these all three will be in one single project, or they will be three different projects?
Also how can I limit my Content Provider to my services and my applications?
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Oct 13, 2010
In my TabHost activity, I want to show an ImageView below the selected tab (the ImageView overlaps the tab content). What would be the best solution to do this?
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Nov 1, 2010
In Android OpenGL ES, I want to be able to switch textures for a given Rectangle. I have one rect and I put two textures, depending on different conditions. I just want to switch between textures.
I followed this code to create the textures: http://blog.poweredbytoast.com/loading-opengl-textures-in-android but it seems that this is only for one texture.
If I use only one texture, it renders fine, but then I don't know how to tell the rect to use another texture (same rect, different texture). Do I do something like "setTexture" with the ID that is generated in loadTextures()? Do I have to have an array with texture names (numbers) that I then change .. I just don't get it..
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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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Feb 19, 2009
I want to judge whether the touch point(x, y) is in a region or not, the region is from a stardard rect by rotating specified degrees, from example, rotate 30 degrees. There is a class named Region in Android, but as I researched, it just supports standard rect, is there any other way to judge whether a point is in an acclivitous rect? How to do it?
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Nov 1, 2010
In Android OpenGL ES, I want to be able to switch textures for a given Rectangle. I have one rect and I put two textures, depending on different conditions. I just want to switch between textures.
I followed this code to create the textures: link text
and they render fine, but then I don't know how to tell the given rect to use another texture. Do I do something like "setTexture" with the ID that is generated in loadTextures() ? Do I have to have an array with texture names (numbers) that I then change .. I just don't get it..
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Dec 3, 2009
What is the use of Invalidate() in android?...
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Sep 18, 2010
How can I draw margin for Image by using Rect object (I need also to change the margin color for every image), so in the end I will have a new Image that surrounded by margins.
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Jul 25, 2009
I have got a problem. How can i create the following rectangle by using Rect class? I mean Diagonal Rectangle. Is it possible through Rect class?? if not then any other way?
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Nov 19, 2009
I have a ListView, its rows each have an image downloaded from the net in a separate thread. When the image is done downloading, I notify my main thread, and need to invalidate the corresponding row if it's on screen.
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Nov 11, 2010
I have an List Activity with a Base Adapter where the contents have changed (example - the rows are reordered). I have tried invalidate.
Code...
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Jan 21, 2010
I am new to Android. Can someone show to me how do I force invalidate a portion of an item in listview? I have listview row item that contains textview and image view. I only want to invalidate text in the textview of a particular item in the listview.
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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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Jul 29, 2009
I have an expandable list view with a static array for the group data and an SQLite database for the child data. It is implemented with the BaseExpandableListAdapter and works great, except, when I edit the database to delete or add children to the list I do not see the changes onscreen. It looks like I can use the registerDataSetObserver method to notify the adapter and expandable list of a data change. What I have to do in the callback to make Android redraw the list after data changes is what I need to know. Can I do it? Documentation on this part of the SDK is a bit sparse and expandable list view example code is not a good match. Can anyone offer advice on how to use a DataSetObserver? It feels like I have to switch over to a Cursor type adapter.
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Oct 15, 2010
what parameters do I pass to this function? invalidate(left, top, right, bottom) for use with google map on android ?
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Mar 10, 2010
I've found that after changing the overlays on a MapView, the changes aren't seen until the user moves the Map, causing a redraw. Is there a way to force this redraw?
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Sep 29, 2010
I'm implementing a fairly standard app with the Android sdk that involves drawing using the SurfaceView, SurfaceHolder, Callback setup.
In my main thread (UI thread) I have no drawing or handling of the SurfaceHolder (or the canvas you retrieve with it).
In a separate thread I have the following:
CODE:...............
This code is being executed, throws no exceptions, and has no negative side effects that I can find; however, the unlockCanvasAndPost() call never causes onDraw() to be called.
In other words, unlockCanvasAndPost() does not cause a redraw of the SurfaceView.
Any ideas what could cause this symptom? I have plenty of java experience, a fair amount of android experience, and a lot of debugging experience and cannot track this one down.
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Sep 7, 2009
does rooting invalidate insurance on orange care?
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Sep 20, 2010
I want to get a set of Views to redraw after I change some drawing parameters. I'm calling invalidate() and forceLayout() on the parent of the Views but nothing happens. If I rotate the screen then the Views redraw correctly using the new parameters, as you would expect. What else do I need to do to get the Views to redraw?
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Nov 22, 2010
I have a linearlayout that is filled with texviews dynamically when i click on a button , but the content of linearlayout doesn't appear, how can i redraw it?
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Jun 1, 2010
I have a custom view that fills my entire screen. (A piano keyboard) When a user touches the key, it causes invalidate() to be called and the whole keyboard gets redrawn to show the new state with a touched key.
Currently the view is very simple, but I plan to add a bit more nice graphics. Since the whole keyboard is dynamically rendered this would make redrawing the entire keyboard more expensive.
So I thought, let's look into partial redrawing. Now I call invalidate(Rect dirty) with the correct dirty region. I set my onDraw(Canvas canvas) method to only draw the keys in the dirty region if I do indeed want a partial redraw. This results in those keys being drawn, but the rest of the keyboard is totally black/not drawn at all.
Am I wrong in expecting that calling invalidate(Rect dirty) would "cache" the current canvas, and only "allows" drawing in the dirty region?
Is there any way I can achieve what I want? (A way to "cache" the canvas and only redraw the dirty area?"
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Oct 7, 2010
I have a RadioGroup view inside a LinearLayout. The radio buttons are added from dataList. If I call the code below from inside onCreate, the correct button is checked. However the dataList can get updated from time to time and after that happens I call this code again, without destroying the Activity. After that, the view is redrawn but no button is checked. I suspect the RadioGroup checked-button bookkeeping is getting confused by the removeAllViews call. Any ideas what might be going wrong?
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Apr 15, 2010
I have created a custom component in my program by extending a ViewGroup. This component listens to touch events and are supposed to start animations when the user has move their finger past some certain points.I'm able to start animations while the user is touching the screen. But I'm not able to start animations if the user doesn't move their finger. It's probably that the phone thinks it doesn't have to update the screen if the user isn't moving their finger.I added some logs and according to them the animation starts and ends but it doesn't draw on the screen. I have the same problems when starting an animation with a timer.I use AlphaAnimations and Translate Animations on ImageViews. I have tried to use invalidate() both on the component and the ImageView but it doesn't help.Anyone who has an idea how to solve this?
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Oct 26, 2010
I am running into an issue with the way my asynctasks are executed. Here's the problem code:
firstTask = new background().new FirstTask(context);
if(firstTask.execute().get().toString().equals("1"))
secondTask = new background().new SecondTask(context);
What I'm doing here is creating a new asynctask object, assigning it to firstTask and then executing it. I then want to fire off a separate asynctask when the first one is done and making sure it returns a success value (1 in this case). This works perfectly on Android 2.0 and up. However, I am testing with Android 1.5 and problems start popping up. The code above will run the first asynctask but doInBackground() is never called despite onPreExecute() being called. If I am to execute the first task without the get() method, doInBackground() is called and everything works as expected. Except now I do not have a way to determine if the first task completed successfully so that I can tell the second task to execute. Is it safe to assume that this is a bug with asynctask on Android 1.5? Especially since the API says that the get method has been implemented since API 3. Is there any way to fix this? Or another way to determine that the first task has finished?
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Jun 15, 2010
I have a listlayout with items in it that looks like this:
There is first an ImageView (the light) and then two textViews. All of this inside a TableLayout. (source here: http://code.google.com/p/switchctrl/source/browse/trunk/android/res/layout/device_switch.xml)
I want to have a rotating animation of a loading indicator Ontop of this light when this particular device (light) performs an action or an action is performed on it.
How do I put an animation ontop of this light imageview?
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Jun 1, 2009
I have a ListView containing a few different type of items, all having their own background image and font color. In my first implementation I implemented each type of item as its own layout with the background image etc defined in XML (and implemented Adapter.getView() so that it only reuses convertView if it's of the correct type). This works fine but the performance is not that great while scrolling since I'm inflating quite a few Views due to convertView mismatches, so instead I tried using the same layout for all items (to benefit fully from convertView reuse) and changing the background image and font size in runtime. I even keep the three background Drawables I need as members to save time decoding them from a resource for each item, and call View.setBackgroundDrawable() from Adapter.getView(). The problem is, sometimes the 9-patch is not correctly wrapped around the content of the list item when using this approach. While scrolling it usually looks correct but when the scrolling stops, or sometimes when I just tap anywhere on the list, the background 9-patch of some large items starts flickering and is either cropped or resized to its original PNG size rather than stretched to wrap the content.
First of all, I suspect this is a bug? Any ideas why this happens? Could it be that the View is not always measured to reflect the changed content when the 9-patch is applied? I have tried adding an extra call to View.invalidate() but it doesn't solve the problem. Second, does this approach sound reasonable at all, or how should I go about to optimize this scenario?
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