获取前台进程包名（ForegroundProcess）

在之前我们可以通过下面的方式获取到前台进程的包名

public String getForegroundApp(Context context) {      ActivityManager mActivityManager =          (ActivityManager) mContext.getSystemService(Context.ACTIVITY_SERVICE);          if (mActivityManager.getRunningTasks(1) == null) {              return null;          }          ActivityManager.RunningTaskInfo mRunningTask =                      mActivityManager.getRunningTasks(1).get(0);          if (mRunningTask == null) {              return null;          }          String pkgName =  mRunningTask.topActivity.getPackageName();          return pkgName;    }  

最新的Android版本中google已经收紧权限了，只能获取到自己APP的进程信息，所以我们可以通过下面的方式获取前台进程。

    public static String getForegroundApp() {        File[] files = new File("/proc").listFiles();        int lowestOomScore = Integer.MAX_VALUE;        String foregroundProcess = null;        for (File file : files) {            if (!file.isDirectory()) {                continue;            }            int pid;            try {                pid = Integer.parseInt(file.getName());            } catch (NumberFormatException e) {                continue;            }            try {                String cgroup = read(String.format("/proc/%d/cgroup", pid));                String[] lines = cgroup.split("\n");                String cpuSubsystem = null;                String cpuaccctSubsystem = null;                // 我们取cpu和cpuacct两行数据                for (String s : lines) {                    if (s.contains(":cpu:")) {                        cpuSubsystem = s;                    }                    if (s.contains(":cpuacct:")) {                        cpuaccctSubsystem = s;                    }                }                if (!cpuaccctSubsystem.endsWith(Integer.toString(pid))) {                    // not an application process                    continue;                }                if (cpuSubsystem.endsWith("bg_non_interactive")) {                    // background policy                    continue;                }                int uid = Integer.parseInt(cpuaccctSubsystem.split(":")[2]                        .split("/")[1].replace("uid_", ""));                if (uid >= 1000 && uid <= 1038) {                    // system process                    continue;                }                int appId = uid - AID_APP;                int userId = 0;                // loop until we get the correct user id.                // 100000 is the offset for each user.                while (appId > AID_USER) {                    appId -= AID_USER;                    userId++;                }                if (appId < 0) {                    continue;                }                // u{user_id}_a{app_id} is used on API 17+ for multiple user                // account support.                // String uidName = String.format("u%d_a%d", userId, appId);                File oomScoreAdj = new File(String.format(                        "/proc/%d/oom_score_adj", pid));                if (oomScoreAdj.canRead()) {                    String str = read(oomScoreAdj.getAbsolutePath());                    int oomAdj = Integer.valueOf(str);                    if (oomAdj != 0) {                        continue;                    }                }                String cmdline = read(String.format("/proc/%d/cmdline", pid));                if (cmdline.contains("com.android.systemui") || cmdline.contains("dirac")) {                    continue;                }                int oomscore = Integer.parseInt(read(String.format(                        "/proc/%d/oom_score", pid)));                if (oomscore < lowestOomScore) {                    lowestOomScore = oomscore;                    foregroundProcess = cmdline;                }            } catch (IOException e) {                e.printStackTrace();            }        }        return foregroundProcess;    }    private static String read(String path) throws IOException {        StringBuilder output = new StringBuilder();        BufferedReader reader = new BufferedReader(new FileReader(path));        output.append(reader.readLine());        for (String line = reader.readLine(); line != null; line = reader                .readLine()) {            output.append('\n').append(line);        }        reader.close();        return output.toString().trim();// 不调用trim()，包名后会带有乱码    }

当然该方法也有缺点，就是需要进行IO操作，所以速度会比较慢。