How to fetch and replace image's background color in onTouch event

Question

Basically there are two hindrances as follows:

1. I want to fetch the background color of a image at the coordinate that the cursor was clicked. The code is fetching the color as well as the coordinate for the first time. But when I'm clicking again an error occurs.
2. I would like to fetch the color of the image in hex not in RGB integer values and then change that particular color with mine in that particular area wherever the color was found.

Here's the code:

private ImageView mImageView;
private Button button;

@Override
protected void onCreate(Bundle savedInstanceState)
{
    super.onCreate(savedInstanceState);
    setContentView(R.layout.vp_view_img);

    if(getIntent().hasExtra("BitmapImage")) 
    {
        final Bitmap bitmap = (Bitmap) getIntent().getParcelableExtra("BitmapImage");

        mImageView = (ImageView) findViewById(R.id.canvas_image);
        mImageView.setImageBitmap(bitmap);
        mImageView.setOnTouchListener(new ImageView.OnTouchListener()
        {     
            @Override   
            public boolean onTouch(View v, MotionEvent event)
            {
                int x = (int)event.getX();
                int y = (int)event.getY();

               /*Toast.makeText(getBaseContext(), "Touch coordinates : "
                                     + String.valueOf(event.getX()) + "x"
                                     + String.valueOf(event.getY()),
                                     Toast.LENGTH_SHORT).show();*/
                ImageView imageView = (ImageView) v;
                Bitmap bitmap = ((BitmapDrawable)imageView.getDrawable()).getBitmap();
                int pixel = bitmap.getPixel(x,y);
                int redValue = Color.red(pixel);
                int blueValue = Color.blue(pixel);
                int greenValue = Color.green(pixel);

                Toast.makeText(getBaseContext(), "Color Code :"+
                    redValue+blueValue+greenValue,Toast.LENGTH_SHORT).show();
                return true;    
                }    
            });
    }
    else
    {
        Toast.makeText(getBaseContext(), 
                "No Image Found", 
                Toast.LENGTH_LONG).show();
    }
}

Answer 1

Let's start with the second question: In order to convert a Color (represented as an Integer) into the corresponding hex value, you should know, that hexadecimal color representations are actually:

#RGB, #RRGGBB, #RRRGGGBBB, #RRRRGGGGBBBB

So you can take the base color components of the color you want, and turn them individually into a hex string, then put them together:

/**
 * Converts the passed integer (color) into it's hexadecimal representation  
 * @param pixel the Color to convert
 * @return a String: the <code>pixel</code> parameter in #RRGGBB format 
 */
private String rgbToHex(int pixel)
{
    int redValue = Color.red(pixel);
    int blueValue = Color.blue(pixel);
    int greenValue = Color.green(pixel);
    return "#" + getBaseColorAsHex(redValue) + 
        getBaseColorAsHex(greenValue) + 
        getBaseColorAsHex(blueValue);
}

/**
 * Returns the hex representation of the <code>baseColor</code>
 * parameter, padding up to 2 characters if necessary.
 * @param baseColor the color whose hex representation is needed
 * @return the hex code for the passed parameter
 */
private String getBaseColorAsHex(int baseColor)
{
    final String hex = Integer.toHexString(baseColor);
    return (hex.length() == 1 ? '0' : "") + hex;
}

As of the first question, you should provide your logcat output: without any knowledge of the error, we cannot help solving it.

Also, you should consider splitting up your question in two for real, because in this form it does not fit into the Stack Overflow's guidelines!

Edit: About the first question asked: One serious problem could be that the image you are analyzing is smaller than the screen, and it is stretched, so when you tap on the screen and retrieve the x and y coordinates, mirroring them onto the image fails due to it's size: the value of x or y might be greater then the width, respectively the height of your bitmap.

Unless you use try-catch blocks and log the exception, you won't be able to tell where the problem really is.

Answer 2

how about use selector?

in res/drawable folder, make xml file like below code

<?xml version="1.0" encoding="UTF-8"?>
<selector xmlns:android="http://schemas.android.com/apk/res/android">
    <item android:state_selected="true" android:color="@color/white"/> <!-- selected -->
    <item android:state_pressed="true" android:color="@color/white" />  <!-- pressed -->
    <item android:color="@color/black" />
</selector>