重写返回键

private long tempTime = 0;/** * 双击退出 */@Overridepublic void onBackPressed() {    long firstClick = System.currentTimeMillis();    if (firstClick - tempTime < 500) {        ToastUtil.cancel();        super.onBackPressed();    } else {        ToastUtil.show(this, "再按一次退出");    }    tempTime = firstClick;}

Toast工具类

package com.bitmain.btccom.utils;import android.content.Context;import android.widget.Toast;/** * Created by kongqw on 2015/11/21. */public final class ToastUtil {
         private static Toast mToast;    // 工具类私有化    private ToastUtil() {    }    // 单例模式 显示Toast    public static void show(Context context, String text) {        if (null == mToast) {            mToast = Toast.makeText(context, "", Toast.LENGTH_SHORT);        }        mToast.setText(text);        mToast.show();    }    // 关闭Toast    public static void cancel() {        if (null != mToast)            mToast.cancel();    }}