Develop Reference

canvas2Draw - how to connect view class to the canvas2

full code I'm new in android studio and I'm having problem with drawing.
Upon execution it does not work
public class MainActivity extends AppCompatActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
View eissa=new eissa(this);
setContentView(eissa);
}
}
class eissa extends View {
private Canvas canvas2;
private Bitmap backingbitmap;
public eissa(Context context) {
super(context);
backingbitmap=Bitmap.createBitmap(100,100,Bitmap.Config.ARGB_8888);
canvas2= new Canvas(backingbitmap);
}
#Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
canvas.drawCircle(0,50,100,null);
canvas2.drawCircle(0,50,100,null);
canvas.drawBitmap(backingbitmap,0,0,null);
}
}

2.
There is a problem with the canvas.drawCircle() because there is no Paint argument (last one). The drawCircle doc says : "Paint: The paint used to draw the circle This value cannot be null."
So you can create a Paint in the constructor to pass to the drawCircle methods:
class eissa extends View {
private Canvas canvas2;
private Bitmap backingbitmap;
Paint viewPaint;
public eissa(Context context) {
super(context);
backingbitmap=Bitmap.createBitmap(100,100,Bitmap.Config.ARGB_8888);
canvas2= new Canvas(backingbitmap);
viewPaint = new Paint();
viewPaint.setColor(0xFFFF0000); // set your desired color here context.getColor(R.color....);
viewPaint.setStrokeWidth(4);
}
#Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
canvas.drawCircle(0, 50, 100, viewPaint);
canvas2.drawCircle(0, 50, 100, viewPaint);
canvas.drawBitmap(backingbitmap, 0, 0, null);
}
}
1.
The view's dimensions are not specified anywhere causing the platform to use the default LayoutParams which have the layout_width and layout_height equal to WRAP_CONTENT so the view is not visible. To address ui issues you can use Tools / Layout inspector which can help identify the cause (incorrect dimensions).
Here is a good tutorial about measuring custom views.
The quickest fix would be to specify dimensions using LayoutParams in setContentView:
// replace setContentView() in onCreate() with this
ViewGroup.LayoutParams lp = new ViewGroup.LayoutParams(ViewGroup.LayoutParams.MATCH_PARENT,
ViewGroup.LayoutParams.MATCH_PARENT);
setContentView(eissa, lp);

How to display a simple ImageButton on a customly created view?

I've been browsing the entire internet, but I could not find any answer to this question. I want to create a background, some image buttons, along with a bunch of moving graphics (circles). Since I do not know how to overwrite a xml layout with moving graphics, I chose to customly create my view, draw the background, the imageButtons and the circles (2D graphics).
public class GameView extends View implements UtilConstants
since I extended the View class, I had to call the super class constructor in my constructor
GameView(Context context) {
super(context);
this.context = context;
this.paint = new Paint();
}
and to implement the onDraw method, which acts like the java paintComponent
#Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas); // necessary for some reason
setGridBackground(); // sets the background
paint.setColor(Color.parseColor("#FF0000"));
canvas.drawCircle(this.x += 10, 300, 20, paint); //moves my graphics (ball) within the screen
drawScoreInLeftUpperCorner(canvas, 20); // paints a string text on the screen
setAbilitiesImages(); // places some imageButtons
try {
Thread.sleep(THREAD_REFRESH_RATE_MS);
} catch (InterruptedException ex) {
System.out.println(ex);
}
invalidate();
}
Now, to get to my problem:
I do not know how to set those ImageButtons !!! I am trying
private void setAbilititesImages() {
ImageButton imageButton = new ImageButton(this.context); // is this ok to put the argument this.context??
imageButton.setLayoutParams(new LinearLayout.LayoutParams(ViewGroup.LayoutParams.WRAP_CONTENT, ViewGroup.LayoutParams.WRAP_CONTENT));
imageButton.setImageResource(R.drawable.monster); // set my resource
RelativeLayout relativeLayout = findViewById(R.id.in_game_layout); // what is the purpose of this???
if (relativeLayout != null) { // it never enters this if, relativeLayout is always null
relativeLayout.addView(imageButton);
}
}
Aaaaand the image button never shows up...why is it necessary to use Relative/Linear layouts? That R.id.in_game_layout I created is just an empty RelativeLayout xml. Can't I just use something like
imageButton.setImageResource(R.drawable.monster); // set my resource
imageButton.setBounds(.....);
(View)this.add(imageButton); ???

ImageButton requires a parent view to be hosted in it. The parent View can be a RelativeLayout, a linearlayout or a ConstraintLayout.
In your case, the instance relativeLayout is always null because you not specify the view parent in which you do findViewById.
You should make something like :
RelativeLayout relativeLayout = view.findViewById(R.id.in_game_layout);

You need to add layout param to your parent Relative layout also to display your Image button appropriately.
Example
RelativeLayout relativeLayout = findViewById(R.id.relativeLayout);
RelativeLayout.LayoutParams params = new RelativeLayout.LayoutParams(
ViewGroup.LayoutParams.WRAP_CONTENT, ViewGroup.LayoutParams.WRAP_CONTENT);
ImageButton imageButton = new ImageButton(this);
imageButton.setImageDrawable(getResources().getDrawable(R.drawable.ic_launcher_background,null));
relativeLayout.addView(imageButton,params);

Rotate and scale image at same time

I have this code and I want to rotate and scale an ImageView at the same time:
public class LayoutPunteggio extends RelativeLayout {
TextView ok;
LayoutInflater inflater;
RotateAnimation rotateAnimation1;
public LayoutPunteggio(Context context) {
super(context);
inflater = LayoutInflater.from(context);
init();
}
public void init() {
mano = new ImageView(getContext());
mano.setImageResource(R.drawable.mano);
mano.setX(100);
mano.setY(100);
addView(mano);
startScale(mano);
rotate();
}
public void rotate() {
rotateAnimation1.setInterpolator(new LinearInterpolator());
rotateAnimation1.setDuration(1000);
rotateAnimation1.setRepeatCount(-1);
mano.startAnimation(rotateAnimation1);
}
public void startScale(View view){
ScaleAnimation animation;
animation=new ScaleAnimation(1,2,1,2,1000, 1000);
animation.setDuration(1000);
view.startAnimation(animation);
}
}
I tried to apply the method rotate() then startScale(), but this doesn't work for both.
Does anyone have a solution?

You can use a library called NineOldAndroids.
There you have playTogether function of the AnimatorSet.
AnimatorSet animation = new AnimatorSet();
animation.playTogether(
ObjectAnimator.ofFloat(yourImageView, "rotation", 0, 360),
ObjectAnimator.ofFloat(yourImageView, "scaleX", 1, 2f),
ObjectAnimator.ofFloat(yourImageView, "scaleY", 1, 2f)
);
animation.setDuratio(1000);
animation.start();
You can also add a listener
animation.addListener(new AnimationListener(){
onAnimationStart....
onAnimationRepeat...
onAnimationEnd...
onAnimationCancel...
});

You can use this library: https://github.com/Yalantis/uCrop
Just pick the image or code the image path(if you don't want the user to change the image).

I guess you should use AnimationSet:
AnimationSet as = new AnimationSet(true);
// config rotation animation
RotateAnimation ra = new RotateAnimation(...);
ra.setDuration(1000);
...
// config scale animation
ScaleAnimation sa = new ScaleAnimation(...);
sa.setDuration(1000);
...
// Add animations
as.addAnimation(ra);
as.addAnimation(sa);
as.start();

Starting from Honeycomb animations are lot easier to implement, source: ViewPropertyAnimator
For instance changing coordinates of view:
ObjectAnimator animX = ObjectAnimator.ofFloat(myView, "x", 50f);
ObjectAnimator animY = ObjectAnimator.ofFloat(myView, "y", 100f);
AnimatorSet animSetXY = new AnimatorSet();
animSetXY.playTogether(animX, animY);
animSetXY.start();

Bitmap create null pointer exception

Here is my xml file : Image view im trying to access
<ImageView
android:layout_width="350dip"
android:layout_height="400dip"
android:id="#+id/imgview"
android:background="#drawable/pattern"
android:layout_centerVertical="true"
android:layout_alignParentRight="true"
android:layout_alignParentEnd="true" />
Here is my code.. kindly review the code and let me know where i am doin things wrong i have searched all over the internet just cant try to figure it out how to make bitmap object and draw canvas on image view
public class MainActivity extends Activity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
setContentView(new SampleView(this));
}
private static class SampleView extends View {
private ImageView img;
// CONSTRUCTOR
public SampleView(Context context) {
super(context);
setFocusable(true);
img = (ImageView)findViewById(R.id.imgview);
}
#Override
protected void onDraw(Canvas canvas) {
Paint paint = new Paint();
canvas.drawColor(Color.GREEN);
//I keep on getting null pointer exception here
Bitmap b = Bitmap.createBitmap(img.getMeasuredWidth(),img.getMeasuredHeight(), Bitmap.Config.ARGB_8888);
Canvas c = new Canvas(b);
c.drawRect(0, 0, 200, 200, paint);
paint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.SRC));
paint.setTextSize(40);
paint.setTextScaleX(1.f);
paint.setAlpha(0);
paint.setAntiAlias(true);
c.drawText("Your text", 30, 40, paint);
paint.setColor(Color.RED);
canvas.drawBitmap(b, 10,10, paint);
}
}
}

If you're getting a NullPointerException on that line, it means img is null, which either means findViewById(R.id.imgview); returned null, or onDraw is being executed as part of super(context); (not sure if that's the case).

When width or height you want to have in your bitmap exceeds the size of device then you may get this error. You should use createScaledBitmap. This will help you.

Draw canvas on widget android

I'm trying to draw the canvas on widget, but I have nothing. I have a form with imageviev on which the bitmap, which I will draw all the beauty, but it did not draw ... Here is a piece of my code, what it not work?
My provider where i draw
public class MainActivity extends AppWidgetProvider {
private Bitmap bmp;
private RemoteViews views;
public void onUpdate(Context context, AppWidgetManager appWidgetManager, int[] appWidgetIds) {
views = new RemoteViews(context.getApplicationContext().getPackageName(), R.layout.main);
Paint paint = new Paint();
paint.setStyle(Paint.Style.FILL);
paint.setColor(Color.RED);
paint.setTextSize(16);
paint.setAntiAlias(true);
paint.setTypeface(Typeface.MONOSPACE);
Bitmap bmp = Bitmap.createBitmap(100, 16, Bitmap.Config.ALPHA_8);
Canvas c = new Canvas(bmp);
c.drawText("fdgfdgfdgfdfdfdgGFDFGFDDDDG", 0, 0, paint);
views.setImageViewBitmap(R.id.imageView1, bmp);
}
}
and my main.xml
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:id="#+id/widget_layout"
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_margin="8dip"
android:background="#drawable/ic_launcher" >
<ImageView
android:id="#+id/imageView1"
android:layout_width="match_parent"
android:layout_height="match_parent" >
</ImageView>

It looks like you may have several problems, but this may help with a couple.
First your onUpdate method needs to be able to service each of the widgets whose IDs are being passed to you. Note that users can create several instances of your widget on one or more screens at the same time. So the first thing you need to do is create a loop to draw into all of them.
Next, you need to notify the widget manager when each of those widgets is ready to be updated.
You may also need to use a different BitMap depth. ALPHA_8 doesn't work in my test showing only black but ARGB_4444 does.
Note also that you Bitmap and RemoteViews member variables are hiding the ones that you create in the body of your method. I recommend removing the RemoteViews member, and the stack Bitmap.
Putting this all together, here is what the result will look like:
public class MainActivity extends AppWidgetProvider {
private Bitmap bmp = Bitmap.createBitmap(100, 16, Bitmap.Config.ARGB_4444);
public void onUpdate(Context context, AppWidgetManager appWidgetManager, int[] appWidgetIds) {
for(int appWidgetId : appWidgetIds) {
RemoteViews views = new RemoteViews(...);
...
views.setImageViewBitmap(R.id.imageView1, bmp);
appWidgetManager.updateAppWidget(appWidgetId, views);
}
}
You may face other problems as well. For instance, it is important that all graphics calls be performed on the graphics thread. Implementing a widget is much more complicated than an app. Good luck!

try to put different values for x and y. Currently it is drawing but out side the bounds of bitmap... so try that..

You need to call
appWidgetManager.updateAppWidget(appWidgetIds, views);