再按下一次Back键退出应用程序

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package com.example.myactivitytest;

import java.util.ArrayList;
import java.util.Timer;
import java.util.TimerTask;

import android.app.Activity;
import android.os.Bundle;
import android.view.KeyEvent;
import android.widget.Toast;

public class BaseActivity extends Activity {

	Timer timer;
	boolean bFlag = false;// bFlag = false 没有按下back 键
	
	static ArrayList<BaseActivity> mActivities = new ArrayList<BaseActivity>();

	public BaseActivity() {

	}

	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);

		timer = new Timer();
		mActivities.add(this);
		
	}

	@Override
	public boolean onKeyDown(int keyCode, KeyEvent event) {
		if (keyCode == KeyEvent.KEYCODE_BACK) {
			if (bFlag == true) { // 第二按下back键
				for (int i = 0; i < mActivities.size(); i++) {
				   BaseActivity baseActivity = 	mActivities.get(i);
				   baseActivity.finish();
				}
				mActivities.clear();
				return true;
			}

			bFlag = true; // bFlag = false 没有按下back 键
			timer.schedule(new TimerTask() {

				@Override
				public void run() {
					bFlag = false;
				}
			}, 2000);
			Toast.makeText(BaseActivity.this, "再按下一次Back键退出应用程序",
					Toast.LENGTH_LONG).show();
			return true;
		}
		return super.onKeyDown(keyCode, event);
	}

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