How to use a layout's background as a bitmap to convert X and Y to RGB values

问题

I have a layout with the color palette as the background.

Within the layout I added a smaller image as a thumb (which is resized using @dimen to make it smaller, really small, like a crosshair) which should move around as the user drag around the layout above:

How do I use the layout's background as a bitmap so I can use the following code:

f = (FrameLayout) findViewById(R.id.fl);
f.setOnTouchListener(flt);

iv = (ImageView) findViewById(R.id.iv);

View.OnTouchListener flt = new View.OnTouchListener() {

        @Override
        public boolean onTouch(View v, MotionEvent event) {

            float x = event.getX();
            float y = event.getY();
            //int pixel = resizedbitmap.getPixel((int)x,(int) y); //the background of the layout goes here...

            switch (event.getAction()) {
            case MotionEvent.ACTION_DOWN:
                if (x<0) {
                    x = x + 10;
                    iv.setX(x);
                    iv.setY(y);
                }
                if (x>f.getWidth()) {
                    x = x - 10;
                    iv.setX(x);
                    iv.setY(y);
                }
                else {
                    iv.setX(x);
                    iv.setY(y);
                }
                // Write your code to perform an action on down
                break;
            case MotionEvent.ACTION_MOVE:
                if (x<0) {
                    x = x + 10;
                    iv.setX(x);
                    iv.setY(y);
                    inRed = Color.red(pixel);
                    inBlue = Color.blue(pixel);
                    inGreen = Color.green(pixel);
                    Log.d("Colors","R:" +inRed +" G:" +inGreen+" B:" + inBlue);
                }
                if (x>f.getWidth()) {
                    x = x - 10;
                    iv.setX(x);
                    iv.setY(y);
                }
                else {
                    iv.setX(x);
                    iv.setY(y);
                }
                // Write your code to perform an action on contineus touch move
                break;
            case MotionEvent.ACTION_UP:
                // Write your code to perform an action on touch up
                break;
        }
            // TODO Auto-generated method stub
            return true;
        }
    };

The XML is:

<FrameLayout
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@drawable/palette2"
    android:id="@+id/fl" >

    <ImageView
        android:id="@+id/iv"
        android:layout_width="10dp"
        android:layout_height="10dp"
        android:src="@drawable/esquare" />

</FrameLayout>

What I am looking to do is, create a color picker so as the user drags within the layout, the user is presented with the R G B values. Can anyone help me complete the codes?

回答1:

1. Get the pixel with a line like the one you commented out. Use BitMap's getPixel(x,y). You need to keep a bitmap around for this.

2. getPixel() returns a color int, as you can see by checking http://developer.android.com/reference/android/graphics/Bitmap.html Actually, the documentation wrongly suggests that getPixel returns an android.graphics.Color object. It does not. It returns a color int argb.

3. get the components of the color int, c, by calls like this, as you can see by checking http://developer.android.com/reference/android/graphics/Color.html

   int alpha = Bitmap.alpha(c);

   int red = Bitmap.red(c);

Or you can do the bit ops yourself:

int alpha = c >>> 24;
int red = (c >>> 16) & 0xFF;

Does that answer your question?

来源：https://stackoverflow.com/questions/21567226/how-to-use-a-layouts-background-as-a-bitmap-to-convert-x-and-y-to-rgb-values