Android :: Redrawing A View - Using OnKeyListener - OnDraw And Invalidate
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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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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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 9, 2010
Why I can't implement OnKeyListener with parameter View such as on example where parameters are (View v, int keyCode, KeyEvent event) I'm forced to use parameters (DialogInterface dialog, int keyCode, KeyEvent event) but not the View as I want.
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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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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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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 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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Sep 12, 2010
I defined an EditText-field and I want to be informed when the user edits that fields.
So I thought: simple - I add an OnKeyListener and so I did. But even though the text field gets edited (and even displays the entered/modified text) I don't get any callback, i.e. the LOG-output doesn't show up.
CODE:......
why that callback is never called?
Android is really full of oddities! It seems that almost nothing I touched so far worked immediatly as one would expect. And - believe it or not - I have LOTS of experience with GUIs, esp. in Java (AWT, Swing, SWT, you name it...) But Android is a really tough beast!
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Dec 28, 2009
I am using onKeyListener to get the onKey events. It works fine with the normal keyboard. But it does not work with soft keyboard. I am only able to get onKey events for numerics and not alphabets. Is there any workaround to solve this?
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Apr 26, 2010
I have a widget set up and it displays properly in both portrait and landscape when added to each. But when I change orientation it has the problem "Problem Loading Widget". I delete this, re-add the widget, and it displays correctly. Thus, my widget can support both portrait and landscape but it doesn't survive an orientation switch. What am I missing? Do I need to redraw the widget when orientation is changed? Doesn't it do this automatically? Do I need to call onUpdate() somehow?
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Aug 20, 2009
I have a custom ListView and I want to redraw a View inside each row under some circumstances. How would I do that in the ListActivity?
But that seems a waste, redrawing the whole listview. Code...
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Jun 8, 2009
I am having a bit of trouble with my current application. With a button at the beginning of my app, I send out Intents for two activities, one gets a camera object, and starts a preview screen. On top of that, in a separate layout, there is an activity with a translucent view, which shows a resource image (the user is trying to get the image he is actually taking to align with the translucent image) and a couple of textviews displaying a target phone orientation as well as the user's current phone orientation.
when I update the text value of one of my text views in my onSensorChanged() field, the system constantly reallocates 1.22MB and garbage collects it. I can only assume that this is because it is redrawing the entire layout with the translucent image and the text fields, because if I remove the view containing the translucent image from the layout, my text field updates 10x quicker and I don't have ridiculous heap growing / garbage collecting. I am wondering how to go about getting the text fields to update without redrawing the entire surface. I am very new to UI design, and this code was written by someone else before I took over the project, so I don't understand much of what is going on in the custom view he wrote to take care of the translucent image -- called MyView. I will post the code for the layout as well as the MyView code below.................................
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Dec 3, 2009
What is the use of Invalidate() in android?...
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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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May 13, 2010
It seems that my home screen takes a while to load anytime I switch to it. Noticeably lagging are the widgets on that screen (GMail Unread Count x2, Agenda Widget, power control). I figure this is because these widgets are killed when using other programs to free memory. Is this the case? If so, is there anything I can do to change that since I am now rooted?
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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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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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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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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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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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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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Sep 7, 2009
does rooting invalidate insurance on orange care?
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Aug 2, 2010
I am trying to set up a ViewFlipper that changes a SlidingDrawers content each time a button is pressed. So far every view I set up worked fine, but now I am trying to create a ListView (including single_choice_mode) within a child view of the ViewFlipper, but my attempt only let to a NullPointerException. As I only discovered ViewFlipper today, I am not yet familiar with it and may not have understood it completely. if someone could give me a hand and help me find out what I have done wrong, that would be great. Here is what I have done:
The code for the onClick event of the ImageButtons:
public void onClick(View v){
if (v == btnExposure){
mFlipper.setDisplayedChild(0); }
else if (v == btnProperties){
mFlipper.setDisplayedChild(1);}
else if (v == btnSpecialEffects){
mFlipper.setDisplayedChild(2);.............
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Jun 6, 2010
Basically I'm calling the onDraw method like so...
code:...................
You see I'm drawing it on top of a Camera view and the information being drawn is subject to change. I have a listener setup which will update the variables being drawn at the appropriate time but I now want to "refresh" this draw in that listener.
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Aug 17, 2010
I want to build my own custom view which should look like the Crysis-GUI.At first I designed a XML-based Layout and made it visible via the setContentView(int resid)-Method. Worked pretty well.But now I wan't to go a step further and draw in my Layout. So I created a new Class, let it extend View and overrode the onDraw()-Method. So far so good.But how can I still use my XML-Layout? I can't do setContentView anymore, so how could the same effect be achieved?
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Sep 30, 2009
I have a problem with my DDMS in eclipse. In the logcat view appears only this failure: Logcat View fails with "Could not create the view: For input string: "our" "
I uninstalled and reinstalled the adt and ddms already without any change. I can use the logcat in the command line (tools- adt logcat) but this is not as comfortable as using the logcat in eclipse.
More details of this failure message are:
CODE:...............
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