How to listen for an activity and change a setting

Question

I want to write a simple android application that listens for a command such as long press menu button or press home button 3 times and then changes value in /sys/class/mdnie/mdnie/negative to 1 or 0. I have no idea where to begin, I know modifying this value requires root access and I can successfully do this by echo > 1 /sys/class/mdnie/mdnie/negative

Any guidance is appreciated, I need this for a friend who is visually impaired. This application will toggle negative colors for himon some samsung devices and he would like to press the home key 3 times to toggle the negative colors on and off from anywhere on the device.

Possible duplicate of http://stackoverflow.com/questions/18086097/where-to-put-code-for-a-global-hardware-key-listener — Piovezan, Oct 28 '13 at 17:49
Thanks for the reference, the rom we are using allows for launching an app via hardkeys, so hardkey feature aside how would I write a simple app the looks at value at /sys/class/mdnie/mdnie/negative and changes it to a 1 or 0 based on what it already has. This app needs no user interface. — user2929128, Oct 28 '13 at 18:09

Piovezan · Answer 1 · 2013-10-29T10:43:51.477

It shouldn't be difficult. It would be an activity with no associated display that toggles the value and finishes immediately afterwards. The code would look like this (not it is untested code - if you face issues, post them as new StackOverflow questions different from this one):

public class ToggleNegativeColorsActivity extends Activity {

    private static final String FILEPATH = "/sys/class/mdnie/mdnie/negative";

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super(savedInstanceState);

        try {
            String value = readFileAsString(FILEPATH);
            if ("1".equals(value.trim())) {
                writeStringToFile(FILEPATH, "0");
            } else {
                writeStringToFile(FILEPATH, "1");
            }
        catch (IOException e) {
            e.printStackTrace();
        }

        finish();
    }

    // Grabbed from http://stackoverflow.com/questions/1656797/how-to-read-a-file-into-string-in-java
    private String readFileAsString(String filePath) throws IOException {
        StringBuffer fileData = new StringBuffer();
        BufferedReader reader = new BufferedReader(
            new FileReader(filePath));
        char[] buf = new char[1024];
        int numRead;
        while((numRead=reader.read(buf)) != -1){
            String readData = String.valueOf(buf, 0, numRead);
            fileData.append(readData);
        }
        reader.close();
        return fileData.toString();
    }

    // Grabbed from http://stackoverflow.com/questions/1053467/how-do-i-save-a-string-to-a-text-file-using-java
    private void writeStringToFile(String filePath, String value) throws IOException {
        PrintWriter out = new PrintWriter(filePath);
        out.print(value);
        out.close();
    }
}

How to listen for an activity and change a setting

1 Answers1