Develop Reference

Android. Button does not work in Canvas

Button does not work in Canvas. What you need to change / add the caller to a message? The button is created but does not respond when you press. Is it possible that the canvas is over the button?
public class ButtonInCanvas extends AppCompatActivity implements View.OnClickListener {
Button button;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
button = new Button(ButtonInCanvas.this);
button.setOnClickListener(this);
button.setText("OK!");
setContentView(new BtInCanvas(ButtonInCanvas.this));
}
public class BtInCanvas extends View {
public BtInCanvas(Context context) {
super(context);
}
public void onDraw(Canvas canvas){
button.layout(50,50,300,300);
button.draw(canvas);
}
}
#Override
public void onClick(View v) {
Toast.makeText(this,"OK!",Toast.LENGTH_LONG).show();
}
}

Let refer to the link Android drawing button to canvas with custom view?
"You cannot insert a button into canvas. Canvas is an interface for bitmap or a bitmap buffer for a view. You can only draw other bitmap or pixels in it, not insert an object or a widget.
There are some solutions:
as Nikolay suggested, use a FrameLayout and create two layers (views), first your custom view and the second LinerView or RelativeView, which will come on top, where you can have buttons etc
draw an image of a buttun on Canvas then use onTouchEvent in your custom view and test for the coordinates of the touch, then do something... an example for onTouchEvent here: Make certain area of bitmap transparent on touch"

The setOnClickListener method for each View

I wrote the following code and it works well. But I have other purpose. I want to click only on a view to doing the operations.First, Please see the following image:
MY CODE IS AS FOLLOWS:
public class MainActivity extends Activity {
RelativeLayout relativeLayout;
#Override
protected void onCreate(Bundle bundle)
{ super.onCreate(bundle);
relativeLayout = new RelativeLayout(getApplicationContext());
setContentView(relativeLayout);
A a = new A(this);
relativeLayout.addView(a);
a.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
B b = new B(getApplicationContext());
relativeLayout.addView(b);
}
});
}
}
class A extends View {
Paint paint;
A(Context context) {
super(context);
paint = new Paint();
}
#Override
protected void onDraw(Canvas canvas) {
paint.setAntiAlias(true);
paint.setColor(Color.RED);
canvas.drawRect(20,60,100,150,paint);
}
}
class B extends View {
Paint paint;
B(Context context){
super(context);
paint = new Paint();
}
#Override
protected void onDraw(Canvas canvas){
paint.setAntiAlias(true);
paint.setColor(Color.GREEN);
canvas.drawRect(100,150,200,250,paint);
}
}
when I run the above code I can see the green rectangle after press on the red rectangle. But the problem is that when I press another places on the screen I can do this operations also. I want that only I can see the green rectangle to press on the red rectangle and not in the another places on the screen to doing this operations.

Use onTouch event
a.setOnTouchListener(new View.OnTouchListener() {
#Override
public boolean onTouch(View v, MotionEvent event) {
if (event.getX(0)>=20 && event.getY(0)>=60 && event.getX(0)<=160 && event.getY(0)<=150) {
B b = new B(getApplicationContext());
relativeLayout.addView(b);
}
return true;
}
});

You are defining the red square's parameters but not the parameters of the canvas in which you are drawing. You are creating the view (A) without defining the width and height of it, so it is set to match_parent by default, which means it will take the whole size of your RelativeLayout (the whole screen). So, when you click "outside" the red square you are actually clicking the view (A).
Try to define an specific height and width for the view in which you are drawing, like this.
A a = new A(this);
a.setLayoutParams(new RelativeLayout.LayoutParams(300,300));
Remember that LayoutParams takes pixels as parameters, so you should really convert the dps to px as specified here
Also, setting some background colors to your views (relativeLayout, A) will help you visualize what you are doing.

# nukeforum, your guess helped me very much. I thank all of you. My problem was exactly from the canvas and its size. I added the following operation in my code and solved my problem.
relativeLayout.addView(a,70,70);
For A class, I changed as follows:
canvas.drawRect(10,20,30,40,paint);

View onDraw() delegate?

Is there something like a draw delegate for a View instance? I want to do a little bit of drawing for each view in my app. For example:
EditText et = ...;
et.addDrawDelegate(new DrawDelegate()) {
#Override
public void draw(Canvas canvas) {
// do some custom drawing here
}
}
Normally I would just create a custom view class:
public class MyView extends SomeAndroidView {
#Override
public void onDraw(Canvas canvas) {}
}
but since I want to do this for many view types, this doesn't seem as easy as one global delegate.
Thanks

Put a Image over an activity

How I can put an image over an activity (something like the image below) but with the buttons and other widgets under this image receiving the touch events?
image http://images.macworld.com/appguide/images/android/558/2908791394402692/5582908791394402692_1.jpg

You can create a transparent Activity like this How do I create a transparent Activity on Android? and make a Layout with a fullscreen ImageView

I solve the problem override the draw function.
public class TutorialLinearLayout extends LinearLayout {
public TutorialLinearLayout(Context context) {
super(context);
}
#Override
public void draw(Canvas canvas) {
super.draw(canvas);
Bitmap tutorial = BitmapFactory.decodeResource(getResources(), R.drawable.tutorial);
canvas.drawBitmap(tutorial, 0, 0, null);
tutorial.recycle();
}
}

Android drawing button to canvas with custom view?

How can I draw a button on top of the canvas in a custom view? (Preferably on the mid-right side) Is there something I have to call before doing the button.draw(canvas)?
public class MyClass extends View {
public Simulation(Context context) {
super(context);
pauseButton.setText("TestButton");
pauseButton.setClickable(true);
pauseButton.setOnClickListener(new OnClickListener() {
public void onClick(View v) {
Log.i(TAG, "Button Pressed!");
}
});
public onDraw(Canvas canvas) {
super.onDraw(canvas);
pauseButton.draw(canvas);
}
}
Thanks for your time

You cannot insert a button into canvas. Canvas is an interface for bitmap or a bitmap buffer for a view. You can only draw other bitmap or pixels in it, not insert an object or a widget.
There are some solutions:
as Nikolay suggested, use a FrameLayout and create two layers (views), first your custom view and the second LinerView or RelativeView, which will come on top, where you can have buttons etc
draw an image of a buttun on Canvas then use onTouchEvent in your custom view and test for the coordinates of the touch, then do something... an example for onTouchEvent here: Make certain area of bitmap transparent on touch

Why do you need to draw the button yourself? Use a FrameLayout and simply have the button overlayed on your custom view.

Try this
public onDraw(Canvas canvas) {
super.onDraw(canvas);
canvas.save();
pauseButton.draw(canvas);
canvas.restore();
}