源码下载：

运行效果：

按了返回后：

java代码：

package com.example.cest;import android.app.Activity;import android.graphics.drawable.PaintDrawable;import android.os.Bundle;import android.view.Gravity;import android.view.KeyEvent;import android.view.LayoutInflater;import android.view.View;import android.view.View.OnClickListener;import android.view.ViewGroup;import android.widget.Button;import android.widget.PopupWindow;import android.widget.TextView;import android.widget.Toast;public class MainActivity extends Activity {	PopupWindow popupWindow,popupWindoweExit;	Button bu_shi,bu_fou;	TextView view1;	TextView view2;	Button button;	@Override	protected void onCreate(Bundle savedInstanceState) {		super.onCreate(savedInstanceState);		setContentView(R.layout.activity_main);		button=(Button) findViewById(R.id.bu);		button.setOnClickListener(new OnClickListener() {			@Override			public void onClick(View arg0) {				// TODO Auto-generated method stub				popinit();			}		});	}	protected void popinit() {		// TODO Auto-generated method stub		LayoutInflater inflater = LayoutInflater.from(this);		View pop_view = inflater.inflate(R.layout.bujv, null);		view1=(TextView) pop_view.findViewById(R.id.tv1);		view2=(TextView) pop_view.findViewById(R.id.tv2);		                                      //设置下拉按钮父布局的高和宽		popupWindow = new PopupWindow(pop_view,ViewGroup.LayoutParams.FILL_PARENT,ViewGroup.LayoutParams.WRAP_CONTENT);		popupWindow.setFocusable(true);//没这行按钮下拉了，按手机返回会直接退出//		popupWindow.setOutsideTouchable(true);		popupWindow.setBackgroundDrawable(new PaintDrawable());//没这行按钮下拉了不会消失		popupWindow.showAtLocation(pop_view, Gravity.BOTTOM, 0, 0);//PopupWindow显示的位置		view1.setOnClickListener(new OnClickListener() {			@Override			public void onClick(View v) {				// TODO Auto-generated method stub				Toast.makeText(MainActivity.this, "这是注册",Toast.LENGTH_LONG).show();			}		});		view2.setOnClickListener(new OnClickListener() {			@Override			public void onClick(View v) {				// TODO Auto-generated method stub				Toast.makeText(MainActivity.this, "这是登录",Toast.LENGTH_LONG).show();			}		});	}	/*按返回弹出是否退出画面	 * 	 * */	@Override	public boolean onKeyDown(int keyCode, KeyEvent event) {		// TODO Auto-generated method stub		if (keyCode == KeyEvent.KEYCODE_BACK && event.getRepeatCount() == 0) {			popExit();		}		return false;	}	/*用PopupWindow做的退出	 * */	private void popExit() {		// TODO Auto-generated method stub		LayoutInflater inflater = LayoutInflater.from(this);		View pop_view = inflater.inflate(R.layout.exit, null);		bu_shi=(Button) pop_view.findViewById(R.id.bu_exit_shi);		bu_fou=(Button) pop_view.findViewById(R.id.bu_exit_fou);		popupWindoweExit = new PopupWindow(pop_view,200,ViewGroup.LayoutParams.WRAP_CONTENT);		popupWindoweExit.setFocusable(true);		popupWindoweExit.setOutsideTouchable(true);//		popupWindow.setBackgroundDrawable(new PaintDrawable());		popupWindoweExit.showAtLocation(pop_view, Gravity.BOTTOM|Gravity.CENTER_VERTICAL, 0, 150);		bu_shi.setOnClickListener(new OnClickListener() {						@Override			public void onClick(View v) {				// TODO Auto-generated method stub				MainActivity.this.finish();			}		});		bu_fou.setOnClickListener(new OnClickListener() {						@Override			public void onClick(View v) {				// TODO Auto-generated method stub				popupWindoweExit.dismiss();			}		});	}}

点击按钮显示的布局文件bujv.xml:

按返回按钮弹出退出的xml: