android 5.1 获取系统时间写入rtc

1、放一个按钮，直接调用系统的修改时间

Intent intent = new Intent(Settings.ACTION_DATE_SETTINGS);
startActivity(intent);

2、写个线程，每秒获取当前时间，发现时间更改就写入rtc

new Thread(new Runnable() {
            @Override
            public void run() {
                while (true) {
                    runOnUiThread(new Runnable() {
                        @Override
                        public void run() {
                            Date date = new Date();
                            DateFormat df = DateFormat.getDateTimeInstance();
                            Log.i(TAG, "时间time为： " + df.format(date));
                            tv_time_current.setText(df.format(date));
                            //execSuCmd("busybox hwclock -w\n");

                            Log.i(TAG, "时间： " + savetime);
                            long diff = Math.abs(savetime - date.getTime()) / 1000;
                            Log.i(TAG, "时间： " + savetime + "差值：" + diff);
                            savetime = date.getTime();
                            if (diff > 1) {
                                Log.i(TAG, "满足条件，写入RTC");
                                execSuCmd("busybox hwclock -w\n");
                            }
                        }
                    });
                    SystemClock.sleep(1000);
                }
            }
        }).start();

3、su权限的函数：(系统需要有su权限)

    /**
     * 执行Android命令
     *
     * @param cmd 命令
     */
    private static void execSuCmd(String cmd) {
        Process process = null;
        DataOutputStream os = null;
        DataInputStream is = null;
        try {
            process = Runtime.getRuntime().exec("su");
            os = new DataOutputStream(process.getOutputStream());
            os.writeBytes(cmd + "\n");
            os.writeBytes("exit\n");
            os.flush();
            int aa = process.waitFor();
            is = new DataInputStream(process.getInputStream());
            byte[] buffer = new byte[is.available()];
            is.read(buffer);
            String out = new String(buffer);
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            try {
                if (os != null) {
                    os.close();
                }
                if (is != null) {
                    is.close();
                }
                if (process != null) {
                    process.destroy();
                }

            } catch (Exception e) {
            }
        }
    }

参考：

https://www.cnblogs.com/tc310/p/10922464.html