Activity按下2次退出和获取当前时间

先看下onBackPressed和onKeyDown的区别

在Android上有两种方法来获取该按钮的事件

1.直接获取按钮按下事件，此方法兼容Android 1.0到Android 2.1 也是常规方法，直接重写Activity的onKeyDown方法即可，代码如下:

@Override
public boolean onKeyDown(int keyCode, KeyEvent event)  {
    if (keyCode == KeyEvent.KEYCODE_BACK) { //按下的如果是BACK，同时没有重复
       Toast.makeText(ml78.this,"返回键Back键测试",1).show();
        return true;
    }

return super.onKeyDown(keyCode, event);
}

而对于Android 2.0开始又多出了一种新的方法，对于Activity 可以单独获取Back键的按下事件，直接重写onBackPressed方法即可，代码如下

@Override
public void onBackPressed() {
// 这里处理逻辑代码，大家注意：该方法仅适用于2.0或更新版的sdk
return;
}

1  现在实现对根Activity按下2此返回键实现退出

private static boolean isSysExit = false;
    @Override
    public void onBackPressed() {
        // TODO Auto-generated method stub
        if(!isSysExit){
            isSysExit = true;

            DensityUtil.showToast(this, "再按一次退出");
            Timer timer = new Timer();
            timer.schedule(new TimerTask() {

                @Override
                public void run() {
                    // TODO Auto-generated method stub
                    isSysExit =false;
                }
            }, 2000);
        }else {
            finish();
        }
    }

2  在根Activity中重写后退按钮响应事件，当按后退按钮的时候把Activity退置到后台

@Override
    public boolean onKeyDown(int keyCode, KeyEvent event) {
        // TODO Auto-generated method stub
        //当按下返回键时吧Activity退至到后台
        if(keyCode ==KeyEvent.KEYCODE_BACK){
            moveTaskToBack(true);
            return true;
        }

        return super.onKeyDown(keyCode, event);
    }

 @Override
    public boolean onKeyDown(int keyCode, KeyEvent event) {
        if (event.getKeyCode() == KeyEvent.KEYCODE_MENU) {
            if (mDrawerLayout.isDrawerOpen(Gravity.LEFT)) {
                mDrawerLayout.closeDrawer(Gravity.LEFT);
            } else {
                mDrawerLayout.openDrawer(Gravity.LEFT);
            }
            return true;
        } else if (event.getKeyCode() == KeyEvent.KEYCODE_BACK) {
            if (mDrawerLayout.isDrawerOpen(Gravity.LEFT)) {
                mDrawerLayout.closeDrawer(Gravity.LEFT);
            } else {
                if ((System.currentTimeMillis() - DOUBLE_CLICK_TIME) > 2000) {
                    showToast(getString(R.string.double_click_exit));
                    DOUBLE_CLICK_TIME = System.currentTimeMillis();
                } else {
                    getBaseApplication().exitApp();
                }
            }
            return true;
        }
        return super.onKeyDown(keyCode, event);
    }

获取时间从http://blog.csdn.net/kookob/article/details/6885383粘贴来的

    package com.ob;  

    import java.text.ParseException;
    import java.text.SimpleDateFormat;
    import java.util.Calendar;
    import java.util.Date;  

    public class DateTest {  

        public static void main(String[] args) throws ParseException {
            Calendar now = Calendar.getInstance();
            System.out.println("年: " + now.get(Calendar.YEAR));
            System.out.println("月: " + (now.get(Calendar.MONTH) + 1) + "");
            System.out.println("日: " + now.get(Calendar.DAY_OF_MONTH));
            System.out.println("时: " + now.get(Calendar.HOUR_OF_DAY));
            System.out.println("分: " + now.get(Calendar.MINUTE));
            System.out.println("秒: " + now.get(Calendar.SECOND));
            System.out.println("当前时间毫秒数：" + now.getTimeInMillis());
            System.out.println(now.getTime());  

            Date d = new Date();
            System.out.println(d);
            SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
            String dateNowStr = sdf.format(d);
            System.out.println("格式化后的日期：" + dateNowStr);  

            String str = "2012-1-13 17:26:33";  //要跟上面sdf定义的格式一样
            Date today = sdf.parse(str);
            System.out.println("字符串转成日期：" + today);
        }
    }  

输出结果：

年: 2012
月: 1
日: 13
时: 17
分: 28
秒: 19
当前时间毫秒数：1326446899902
Fri Jan 13 17:28:19 CST 2012
Fri Jan 13 17:28:19 CST 2012
格式化后的日期：2012-01-13 17:28:19
字符串转成日期：Fri Jan 13 17:26:33 CST 2012