How to kill currently running task in android

Question

I am trying to build a task killer type of app in android. I can show the list of currently running task using ActivityManager but facing problem in killing the task.

Here is what i am doing to get the list of currently running task :

ActivityManager am = (ActivityManager) context.
            getSystemService(Activity.ACTIVITY_SERVICE);
List<RunningTaskInfo> a = am.getRunningTasks(Integer.MAX_VALUE);

PackageManager pack = this.getPackageManager();

for(int i = 0; i < a.size(); i++) {
    String packageName = a.get(i).topActivity.getPackageName();
    Drawable d = null;
    String appName = "";

    try {
        d = pack.getApplicationIcon(packageName);
        appName = (String)pack.getApplicationLabel(pack.getApplicationInfo(packageName,PackageManager.GET_META_DATA));
    } catch (NameNotFoundException e) {
        e.printStackTrace();
    }
    
    packName.add(packageName);  //arraylist of package name
    apps.add(appName);          // arraylist of app name
    icons.add(d);               //arraylist of icons
}

It worked for me But now as I am trying to kill the task using killBackgroundProcesses :

am.killBackgroundProcesses(package name);

It did not work . Also killBackgroundProcesses method is available in API level 2.2 then how can i perform the same task in previous API level such as 1.6 etc.

Is there any other way to show the currently active apps and kill them?