Android-获取线程的返回值

Question

I start with Android and Java, and my English is not very good (sorry). I'm doing a application which compare 2 pictures taking by the camera and return a float value = a ratio of identical pixels in the 2 pictures.

public static float comparePic(String img_1, String img_2){
    Bitmap bitmap1 = BitmapFactory.decodeFile(img_1);
    Bitmap bitmap2 = BitmapFactory.decodeFile(img_2);
    int equ = 0;
    //get one height and one width because we assume that pictures have always same sizes
    int h = bitmap1.getHeight();
    int w = bitmap1.getWidth();
    for(int y=0;y<h;y++){
        for (int x=0;x<w;x++){
            int pixel1 = bitmap1.getPixel(x,y);
            int pixel2 = bitmap2.getPixel(x,y);
            //alpha doesn't matter, they're jpg
            int redValue1 = Color.red(pixel1);
            int redValue2 = Color.red(pixel2);
            int greenValue1 = Color.green(pixel1);
            int greenValue2 = Color.green(pixel2);
            int blueValue1 = Color.blue(pixel1);
            int blueValue2 = Color.blue(pixel2);
            if (redValue1==redValue2 && greenValue1==greenValue2 && blueValue1==blueValue2){
                equ++;
            }
        }
    }
    return (float)equ/(h*w);
}

When I execute it, I have this message : "I/Choreographer﹕ Skipped 730 frames! The application may be doing too much work on its main thread." So I tried to do it with a thread, but I'm always failing because I don't know how to return the value. Futhermore, by skipping frames I guess, the ratio is not correct. I know that it's an asynchonous work, so what can I do ? Thanks !

Answer 1

You can simply add a public (setter-)method in your main class (or wherever you need the value). When your async thread is done call the method with equ as the parameter.

You obviously need to care about thread-safety so consider making the method sychronized.

Answer 2

You should give a try to AsyncTask . It's a class specifically prepared for background processing. It has some drawbacks (it's not good idea to do networking with AsyncTask), but for some picture comparison stuff it is a great tool.

Answer 3

Define an Asynctask with a interface and implement that interface in the main Activity.

That way you can notify that host activity that the background asynctask has completed.