I'm trying to mirror a LinearLayout.
To get this work, I extended LinerLayout to create my own View component.
This is what it looks like:
public class FlipLayout extends LinearLayout implements Runnable {
private boolean isMirroring = true;
private Handler handler;
public FlipLayout(Context context) {
super(context);
this.setWillNotDraw(false);
}
public FlipLayout(Context context, AttributeSet attr) {
super(context, attr);
this.setWillNotDraw(false);
handler = new Handler();
handler.postDelayed(this, 30);
}
#Override
protected void dispatchDraw(Canvas canvas) {
canvas.save();
if (isMirroring) {
canvas.rotate(180, getWidth() / 2, getHeight() / 2);
}
super.dispatchDraw(canvas);
canvas.restore();
}
#Override
public boolean dispatchTouchEvent(MotionEvent event) {
if (isMirroring)
event.setLocation(getWidth() - event.getX(),
getHeight() - event.getY());
return super.dispatchTouchEvent(event);
}
#Override
public void run() {
invalidate();
handler.postDelayed(this, 30);
}
}
That class is working well, but only when implementing the Runnable interface and by calling invalidate() every few milliseconds.
If I only rotate the canvas without invalidating the view, the changes of the child views are not drawn.
Now I'm wondering what's the reason for this behaviour and if theres a way to get it working without the Runnable/Handler implementation.
If I remove the line canvas.rotate(...) the changes of the child views are drawn correctly (this is for example a progressbar which is updating itself frequently.)
I hope someone can help!
Thanks so much.
Chris
It looks normal to me that changing a Gui dynamically would not update the screen. In any Gui framework, they require the programmer to manually request the redraw.
This is because if i change 10 items in my Gui, i don't want to redraw 10 times, but only once at the end. And the framework can't guess when i'm done refactoring the Gui. So i need to explicitely call a refresh method somehow.
Alternatively, you could invalidate you Gui directly when you're done rotating your stuff, and not in a separate thread.
Related
I'm doing a school project. In this project I have to do a program that have one or more ball bouncing in the screen. I did some research on google to help me in this, and I found this code :
public class BouncingBallInside extends View {
private List<Ball> balls = new ArrayList<>();
public BouncingBallInside(Context context, AttributeSet attrs) {
super(context, attrs);
init();
}
public BouncingBallInside(Context context) {
super(context);
init();
}
private void init(){
//Add a new ball to the view
balls.add(new Ball(50,50,100, Color.RED));
}
#Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
//Draw the balls
for(Ball ball : balls){
//Move first
ball.move(canvas);
//Draw them
canvas.drawOval(ball.oval,ball.paint);
}
invalidate(); // See note
}
}
The ball class :
public class Ball{
public int x,y,size;
public int velX = 10;
public int velY=7;
public Paint paint;
public RectF oval;
public Ball(int x, int y, int size, int color){
this.x = x;
this.y = y;
this.size = size;
this.paint = new Paint();
this.paint.setColor(color);
}
public void move(Canvas canvas) {
this.x += velX;
this.y += velY;
this.oval = new RectF(x-size/2,y-size/2,x+size/2,y+size/2);
//Do we need to bounce next time?
Rect bounds = new Rect();
this.oval.roundOut(bounds); ///store our int bounds
//This is what you're looking for ▼
if(!canvas.getClipBounds().contains(bounds)){
if(this.x-size<0 || this.x+size > canvas.getWidth()){
velX=-velX;
}
if(this.y-size<0 || this.y+size > canvas.getHeight()){
velY=-velY;
}
}
}
}
The program works perfecly.
I studied it deeply as good as I could. But after it and after watching the documentation I couldn't understand two thing:
Where and when the method onDraw(Canvas canvas) is called the first time.
Why at the end of onDraw there is invalidate()?
I mean the documentation said :
Invalidate the whole view. If the view is visible, onDraw(android.graphics.Canvas) will be called at some point in the future.
so... if this method is used to call onDraw,why don't call it direcly? what's the difference?
1)The onDraw method will be called by the framework, whenever the view is invalid. A view is invalid when it first comes on screen, so when you set your content view for an activity they layout and all views in it will be measured, laid out, then drawn (via onDraw).
After that the UI thread will call onDraw if needed every 16ms or so (so it draws at 60 FPS).
2)Its marking the view as needing to be redrawn, so the next time the the screen is drawn onDraw will be called. Otherwise it would be skipped, as we could assume it isn't needed.
Why you don't call onDraw directly- efficiency. In a very simple drawing system you would- but drawing is time consuming, you don't want to do it more than you have to. So instead of drawing immediately (which wouldn't work anyway, you wouldn't have the right Canvas to pass to onDraw), you call invalidate and the system will call onDraw if needed at a regular interval.
Note that this isn't particularly good code. In particular, having the onDraw trigger the move which updates the balls location instead of using a timer is icky. Having onDraw call invalidate as a result is also kind of icky. A better solution would be to separate the view, model, and timer into more of an MVC or MVP system.
I'm trying to apply a visual effect to a viewgroup. My idea is to grab a bitmap of the viewgroup, shrink it down, expand it back up, and draw it over the viewgroup to give it a blocky, low quality effect.
I've got most of the way there using this code:
public class Blocker {
private static final float RESAMPLE_QUALITY = 0.66f; // less than 1, lower = worse quality
public static void block(Canvas canvas, Bitmap bitmap_old) {
block(canvas, bitmap_old, RESAMPLE_QUALITY);
}
public static void block(Canvas canvas, Bitmap bitmap_old, float quality) {
Bitmap bitmap_new = Bitmap.createScaledBitmap(bitmap_old, Math.round(bitmap_old.getWidth() * RESAMPLE_QUALITY), Math.round(bitmap_old.getHeight() * RESAMPLE_QUALITY), true);
Rect from = new Rect(0, 0, bitmap_new.getWidth(), bitmap_new.getHeight());
RectF to = new RectF(0, 0, bitmap_old.getWidth(), bitmap_old.getHeight());
canvas.drawBitmap(bitmap_new, from, to, null);
}
}
I simply pass in the canvas to draw on and a bitmap of what needs to be scaled down+up and it works well.
public class BlockedLinearLayout extends LinearLayout {
private static final String TAG = BlockedLinearLayout.class.getSimpleName();
public BlockedLinearLayout(Context context, AttributeSet attrs) {
super(context, attrs);
applyCustomAttributes(context, attrs);
setup();
}
public BlockedLinearLayout(Context context) {
super(context);
setup();
}
private void setup() {
this.setDrawingCacheEnabled(true);
}
#Override
public void draw(Canvas canvas) {
super.draw(canvas);
// block(canvas); If I call this here, it works but no updates
}
#Override
public void onDraw(Canvas canvas) {
// block(canvas); If I call this here, draws behind children, still no updates
}
private void block(Canvas canvas) {
Blocker.block(canvas, this.getDrawingCache());
}
}
The problem I'm having is in my viewgroup. If I run the block method in the viewgroup's draw, it draws over everything but doesn't ever update when child views change. I've traced function calls with Log, and the draw method seems to be running, but nothing changes.
I've also tried implementing this in onDraw. This draws the bitmap behind all the children views, and again they aren't updating.
Can anyone explain how I would go about fixing this?
Try this:
#Override
protected void dispatchDraw(Canvas canvas) {
// call block() here if you want to draw behind children
super.dispatchDraw(canvas);
// call block() here if you want to draw over children
}
And call destroyDrawingCache() and then, buildDrawingCache() each time you change a child.
Draw() method will work well for you.
I'm now trying to make a count time view in a circle shape, when time is passing, the view will reducing his angle. It's used to cover profile photo(a circle shape photo).
Starting with Android API 23, you can use onDrawForeground(Canvas) to draw on top of child views: https://developer.android.com/reference/android/view/View#onDrawForeground(android.graphics.Canvas)
Unlike onDraw() though, be sure to call through to the super class:
#Override
public void onDrawForeground(final Canvas canvas) {
super.onDrawForeground(canvas);
// Your code here
}
For my activity i use 3 custom views stacked.
the lower one is a SurfaceView fullscreen, the middle one is derived from GridView and overrides onDraw to add custom graphic.
The top one is derived directly from View, sits in a corner of the screen and act as a knob to control the others two views (this is the problematic view).
to add a custom animation to this view, i used this pattern:
public class StubKnobView extends View{
private Drawable knob;
private Point knobPos;
private float rotation;
private boolean needsToMove;
public void moveKnob(){
/* ...various calculations... */
this.needsToMove=true;
invalidate(); //to notify the intention to start animation
}
private void updateAnimation(){
/* ........... */
this.needsToMove= !animationComplete;
invalidate();
}
#Override
protected void onDraw(Canvas canvas) {
int saveCount=canvas.getSaveCount();
canvas.save();
canvas.rotate(this.rotation, this.knobPos.x, this.knobPos.y );
this.knob.draw(canvas);
canvas.restoreToCount(saveCount);
if(this.needsToMove){
updateAnimation();
}
}
}
ideally, if there is an animation pending, after each drawing cycle the view should auto invalidate.
right now this doesn't work, to force the animation i have to touch the screen to cause a onDraw cycle.
Using "show screen updates" of Dev tools I see that no screen invalidate/update cycle happen , apart when i click the screen.
specifying the dirty rect also ha no effect.
So, any idea where to look to know why this invalidate/draw cycle does not work the way is intended?
I encontered this situation, and also doubted that invalidate() doesn't make onDraw() called again.
After simplified the business codes, it's turn out that there is a dead loop - exactly too much iterations, which blocks the UI thread.
So, my advice is that make sure the UI thread going smoothly first.
Try something like this with a private class in your View. The idea is not to call invalidate() from within onDraw(). Instead, post it on the running queue. Instantiate the private class in your View constructor and then just call animateKnob.start() when you want the animation. The onDraw() can then just focus on drawing.
public void moveKnob(){
// update the state to draw... KnobPos, rotation
invalidate()
}
private class AnimateKnob{
public void start(){
// Do some calculations if necessary
// Start the animation
MyView.this.post( new Runnable() {
stepAnimation()
});
}
public void stepAnimation(){
// update the animation, maybe use an interpolator.
// Here you could also determine if the animation is complete or not
MyView.this.moveKnob();
if( !animationComplete ){
// Call it again
MyView.this.post( new Runnable() {
stepAnimation()
});
}
}
}
so i created a view called "drawable view"
class DrawableView extends View{
Context mContext;
int touches=0,k,Xoffs,clicks=0;
double x_1 = 0,x_2=0;
private float mLastTouchX, mLastTouchY;
public DrawableView(Context context) {
super(context);
mContext = context;
}
....
#Override
protected void onDraw(Canvas canvas){
Paint myPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
canvas.drawColor(Color.BLUE);
myPaint.setColor(Color.WHITE);
canvas.drawCircle(200, 100, 20, myPaint);
}
..... more code....
}
and it can only be invalidated within the ondraw command! ie: calling "invalidate();" at the end of the ondraw command causes it to loop.
I have tried many times to call g_draw.invalidate(); or g_draw.postInvalidate(); (g_draw is the name of the created Drawable View)from other classes and even the main activity class and it doesnt work. why and how can i fix it?
thanks
If you want continious onDraw invoking try doing it in another thread. Create a thread, and from its run method try doing postInvalidate.
It always worked for me.
Another thing is that when you draw a circle once, next time wont make any difference - it will look the same.
You may want to call invalidate() somewhere in your DrawableView class. For example, if you want your view to redraw itself after any touch event, you would do something like this:
public boolean onTouchEvent( MotionEvent event) {
if(event.getAction() == MotionEvent.ACTION_UP){
invalidate();
}
}
This is how I draw the movable pieces in my puzzle game.
I love the API Demo examples from the Android webpage and used the AnimateDrawable.java to
get started with a WaterfallView with several straight falling images which works great. Now I like the images to stop when they are clicked. I found out that Drawables can't handle events so I changed AnimateDrawable and ProxyDrawable to be extended from View instead and added a Click-Event-Listener and Handler on the parent WaterfallView. The animation still works great, but the handler doesn't, probably because in AnimateDrawable the whole canvas is shifted when the drawabled are animated. How can I change that example so that I can implement an event handler? Or is there a way to find out where exactly my AnimateDrawables are in the view?
So the more general question is: How to add an Event Listener / Handler to an animated View?
Here are my changes to the example above:
AnimateView and ProxyView instead of AnimateDrawable and ProxyDrawable
ProxyView extended from View and all super calls changed to mProxy
I commented out mutate()
The context is still the main Activity which is passed down in the constructors
In the constructors of AnimateView setClickable(true) and setFocusable(true) are called
And here is the important source code of the parent/main WaterfallView:
public class WaterfallView extends View implements OnClickListener {
private Context mContext;
// PictureEntry is just a value object to manage the pictures
private Vector<PictureEntry> pictures = new Vector<PictureEntry>();
public WaterfallView(Context context) {
super(context);
mContext = context;
pictures.add(new PictureEntry(context.getResources().getDrawable(R.drawable.sample_0)));
pictures.add(new PictureEntry(context.getResources().getDrawable(R.drawable.sample_1)));
pictures.add(new PictureEntry(context.getResources().getDrawable(R.drawable.sample_2)));
pictures.add(new PictureEntry(context.getResources().getDrawable(R.drawable.sample_3)));
pictures.add(new PictureEntry(context.getResources().getDrawable(R.drawable.sample_4)));
pictures.add(new PictureEntry(context.getResources().getDrawable(R.drawable.sample_5)));
pictures.add(new PictureEntry(context.getResources().getDrawable(R.drawable.sample_6)));
pictures.add(new PictureEntry(context.getResources().getDrawable(R.drawable.sample_7)));
}
#Override
protected void onDraw(Canvas canvas) {
if(!setup) {
for(PictureEntry pic : pictures) pic.setAnimation(createAnimation(pic));
setup = true;
}
canvas.drawColor(Color.BLACK);
for(PictureEntry pic : pictures) pic.getAnimateView().draw(canvas);
invalidate();
}
private Animation createAnimation(PictureEntry picture) {
Drawable dr = picture.getDrawable();
dr.setBounds(0, 0, dr.getIntrinsicWidth(), dr.getIntrinsicHeight());
Animation an = new TranslateAnimation(0, 0, -1*dr.getIntrinsicHeight(), this.getHeight());
an.setRepeatCount(-1);
an.initialize(10, 10, 10, 10);
AnimateView av = new AnimateView(mContext, dr, an);
av.setOnClickListener(this);
picture.setAnimateView(av);
an.startNow();
return an;
}
#Override
public void onClick(View v) {
Log.i("MyLog", "clicked "+v);
}
}
Are you going to be clicking widgets(buttons, checkboxes, etc)? Or do you want to be able to click anywhere? I think you want the latter. So in that case you'll need this method:
#Override
public boolean onTouchEvent(MotionEvent event) {
// do stuff with your event
}
This method is ONLY called when the event is NOT handled by a view, so I think you may have to remove some of your onClickListener stuff. Refer to here for more info. And as always, experiment.