Develop Reference

Android library overlay rectangle disappears

I have a library that shows a camera preview. I want to add a rectangle overlay on top of the preview. I tried 2 different approaches. But both of them display the rectangle shortly then disappear.
approach (using view.getOverlay)
mPreview.setZOrderMediaOverlay(true);
mPreview.setZOrderOnTop(true);
ViewGroup rootView = (ViewGroup)mActivity.getWindow().getDecorView().findViewById(android.R.id.content);
rootView.addView(mPreview);
final ViewOverlay overlay = mPreview.getOverlay();
final Bracket bracket = new Bracket();
mPreview.post(new Runnable() {
#Override
public void run() {
bracket.setBounds(0, 0, mPreview.getWidth(), mPreview.getHeight());
overlay.add(bracket);
}
});
approach (overriding draw function in surfaceview)
#Override
public void draw(Canvas canvas) {
super.draw(canvas);
paint.setStyle(Paint.Style.STROKE);
paint.setColor(Color.GREEN);
paint.setStrokeWidth(10);
//center
int x0 = canvas.getWidth()/2;
int y0 = canvas.getHeight()/2;
int dx = canvas.getHeight()/3;
int dy = canvas.getHeight()/3;
//draw guide box
canvas.drawRect(x0-dx, y0-dy, x0+dx, y0+dy, paint);
}
mPreview extends SurfaceView
Bracket extends Drawable
UPDATE
If I use setContentView instead of rootView.addView it works as expected. But in this case I can not remove the view.

I used a new Activity and setContentView. That solved the problem.
To remove the view I finished the action.

How to draw a simple line over buttons

I am making a noughts and crosses game and i want to draw a line over the winning combination. The playing grid consists of a grid of buttons and i want the line to be over the top of them. At the moment the line will draw but it will have a black background hiding the grid of buttons even though it is set to transparent.
How would i make the transparency work then clear when i want to start a new game?
I hope that makes sense.
This is the draw class:
public class DrawView extends View {
Paint paint = new Paint(Paint.ANTI_ALIAS_FLAG);
public DrawView(Context context) {
super(context);
paint.setColor(Color.RED);
paint.setStrokeWidth(10);
}
#Override
public void onDraw(Canvas canvas) {
canvas.drawLine(0, 0, 1000, 1000, paint);
}
}
This is the part of the method in the game:
public void checkWin() {
if (squares[1] == 1 & squares[2] == 1 & squares[3] == 1) {
for (int i = 1; i <= 9; i++) {
buttons[i].setEnabled(false);
}
drawView = new DrawView(this);
drawView.setBackgroundColor(Color.TRANSPARENT);
setContentView(drawView);
Intent d = new Intent(this, Win.class);
startActivity(d);

If you want to draw a line with alpha, use :
paint.setAlpha(125);
paint.setColor(Color.RED);
paint.setStrokeWidth(10);
Just remember to set it back after you use it, if you use paint else where.
Note:
0 = completely transparent
255 = completely opaque
Edit: Okay, I think you might be trying to clear the canvas, so it starts off blank.
Draw clear onto it, with PorterDuff to clear it.
#Override
public void onDraw(Canvas canvas) {
canvas.drawColor(Color.TRANSPARENT, PorterDuff.Mode.CLEAR);
canvas.drawLine(0, 0, 1000, 1000, paint);
}
I dont think your setBackgroundColor works because you have overriden the draw method. But I could be wrong, the above code should fix the issue.

Marker position is changing based on the device screen width

In my application,I am setting an image in my imageview. I just need to place a marker on that imageview. I am doing it with onDraw function in my custom image view class.The problem is,for example if I take x position and y position as 40 respectively.The marker position shown above image in my mobile is different when compared with running same application on tablet.
I want a solution such that when I give coordinates then the position of marker on image in mobile and tablet appears same.
Here is the code my main activity:
public class PointOnImageActivity extends Activity
{
#Override
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_point_on_image);
CustomImag ev= new CustomImag(this);
ev.setBackgroundResource(R.drawable.stad);// set background
setContentView(ev);
}
}
Here is the code of my custom imageview class:
public class CustomImag extends ImageView
{
public CustomImag(Context context)
{
super(context);
}
#Override
public void onDraw(Canvas canvas)
{
super.onDraw(canvas);
Paint mPaint = new Paint();
mPaint.setColor(Color.RED);
canvas.drawCircle(40,40,10,mPaint);
}
}

that's because 40 is pixel value, you actually need 40dp instead. so you can convert 40dp to px value dynamically, like this:
int pxValue1 = (int)TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, 40, context.getResources()
.getDisplayMetrics());
int pxValue2 = (int)TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, 10, context.getResources()
.getDisplayMetrics());
canvas.drawCircle(pxValue,pxValue,pxValue2,mPaint);

You have to position your custom View according to the screen dimensions. This way, no matter what size screen displays your app, your positioning will be relative.
In your onDraw(Canvas) method, you can get the screen dimensions and draw the circle using them. In the following example(which is mostly your code), I place the red circle at screen_width / 4 and screen_height / 4:
public class MyCustomImageViewActivity extends Activity{
CustomImag ev;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
ev = new CustomImag(this);
ev.setBackgroundResource(R.drawable.stad);// set background
setContentView(ev);
}
public class CustomImag extends ImageView {
Paint mPaint;
public CustomImag(Context context) {
super(context);
mPaint = new Paint();
}
#Override
public void onDraw(Canvas canvas) {
super.onDraw(canvas);
Point point = new Point();
getWindowManager().getDefaultDisplay().getSize(point);
mPaint.setColor(Color.RED);
canvas.drawCircle(point.x / 4, point.y / 4, 10, mPaint);
}
}
}

Create a layer with black transparent over an activity

I want to create a layer with transparent layer over an activity and I need to make visible only a particular view, say for an example "Login Button". It something mean that making hole on layer exactly the size of the button. Please anyone help me out of this.
Thanks In advance.

Programatically, you can use Canvas to create a layer. Fill the whole thing with your color and cut out a hole.
public class DrawView extends View {
Paint paint = new Paint();
Paint transparentPaint = new Paint;
public DrawView(Context context) {
super(context);
}
#Override
public void onDraw(Canvas canvas) {
//first fill everything with your covering color
paint.setColor(yourTransparentColor);
canvas.drawRect(0, 0, canvas.getWidth(), canvas.getHeight(), paint);
//now clear out the area you want to see through
transparentPaint.setAlpha(0xFF);
transparentPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.CLEAR));
Rect rect=new Rect(left, top, right, bottom);//make this your rect!
canvas.drawRect(rect,transparentPaint);
}
}

If I understand your question correctly
Your parent Layout of the Activity will be a RelativeLayout. In your parent layout at the bottom add another child RelativeLayout that implments the match_parent parameters for both width and height. You can then set a color like this #99000000 to it's background. This will give you a black transparent layer over your parent.
Something like this
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:id="#+id/parentLayout"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="#FFFFFF">
<!-- here you add your activities views ect... -->
<RelativeLayout
android:id="#+id/childLayout"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="#99000000">
<!-- This will be your overlay so here you can add your login button ect -->
</RelativeLayout>
</RelativeLayout>
I didn't test this but it should solve your issue

On following "HalR" Steps , I was able to achieve the transparent background Thanks to him and found some of you are getting pitch black on the cut made over transparent layer is due to Graphic rendering . that can be enabled using below code inside onDraw method
` #Override
public void onDraw(Canvas canvas) {
if (android.os.Build.VERSION.SDK_INT >= 11) {
setLayerType(View.LAYER_TYPE_SOFTWARE, null);
}
.....
..... // your draw rect creation and other stuff `
which will let you have the transparent area by eliminating the Pitch black color

If i understood your question then this is what you wanted:
You tried to overlay a transparent view on your activity and cut out holes to see few stuffs.
here i found an useful example which shows how can you cut out bitmaps and combine them. i would suggest for your problem just take the part of cutting the bitmap and remember to set the imageview backgroung with opacity as shown here
android:background="#00ffffff"
here is the layout i created
<ImageButton
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:background="#android:color/transparent"
android:src="#drawable/ic_launcher"
android:layout_alignParentRight="true"
android:layout_alignParentBottom="true"/>"
<ImageView
android:id="#+id/img"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="#00ffffff"
android:scaleType="centerCrop" >
</ImageView>
</RelativeLayout>
and this is my maniactivity
public class MainActivity extends Activity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
ImageView iv = (ImageView) findViewById(R.id.img);
Bitmap foreground = BitmapFactory.decodeResource(getResources(), R.drawable.android_cat_wanted);
foreground = punchAHoleInABitmap(foreground);
iv.setImageBitmap(foreground);
}
private Bitmap punchAHoleInABitmap(Bitmap foreground) {
Bitmap bitmap = Bitmap.createBitmap(foreground.getWidth(), foreground.getHeight(), Bitmap.Config.ARGB_8888);
Canvas canvas = new Canvas(bitmap);
Paint paint = new Paint();
canvas.drawBitmap(foreground, 0, 0, paint);
paint.setAntiAlias(true);
paint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.CLEAR));
float radius = (float)(getScreenSize().x *.35);
float x = (float) ((getScreenSize().x*.5));
float y = (float) ((getScreenSize().y*.5));
canvas.drawCircle(x, y, radius, paint);
return bitmap;
}
#SuppressLint("NewApi")
private Point getScreenSize() {
WindowManager window = (WindowManager) getSystemService(Context.WINDOW_SERVICE);
Display display = window.getDefaultDisplay();
Point size = new Point();
display.getSize(size);
return size;
}
}
hope you find it useful

Change Background

I am new to android and I have an image in my drawable folder which I was able to load as my background, now I would like to draw on top of the background but havent been able to, how can achieve this... I have the following, all i want is to draw a circle on top of the image background
<?xml version="1.0" encoding="utf-8"?>
<FrameLayout android:id="#+id/my_view"
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:background="#drawable/background">
</FrameLayout>
//MY ACTIVITY
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
}
//IN MY VIEW CLASS
public GameView(Context context, float x, float y, int r) {
super(context);
setFocusable(true);
mPaint.setColor(Color.YELLOW);
this.x = x;
this.y = y;
this.r = r;
}
#Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
canvas.drawCircle(x, y, r, mPaint);
}

To set the image as background use ImageView in Absolute Layout.Enter code to set img as background :
android:background="#drawable/icon1"
Now you would be able to have circle over the image view

use ImageView in xml file & set what u want to draw on background.