点击按钮显示弹出框

package com.briup.dialog;

import android.app.Activity;
import android.app.AlertDialog;
import android.content.DialogInterface;
import android.content.DialogInterface.OnClickListener;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.Toast;

public class MainActivity extends Activity implements View.OnClickListener {
	private Button btn1;

	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);
		btn1 = (Button) findViewById(R.id.btn1);
		btn1.setOnClickListener(this);
	}

	@Override
	public void onClick(View v) {
		// TODO Auto-generated method stub
		int id = v.getId();
		switch (id) {
		case R.id.btn1:
			dialog();
			break;

		default:
			break;
		}
	}

	// 基本弹出框
	public void dialog() {
		// 弹出框类
		AlertDialog.Builder alert = new AlertDialog.Builder(this);
		alert.setIcon(R.drawable.ic_launcher);//设置弹出框图标
		alert.setTitle("警告");//设置标题
		alert.setMessage("你肯定要花费20个金币获取答案吗？");//设置内容
		alert.setCancelable(true);//点击其余位置是否消失，默认true能够消失
		alert.setPositiveButton("确认",new OnClickListener() {
			public void onClick(DialogInterface dialog, int which) {
				// TODO Auto-generated method stub
			  Toast.makeText(MainActivity.this, "确认成功", Toast.LENGTH_LONG).show();
			  dialog.dismiss();//关闭弹出框
			}
		});
		alert.setNegativeButton("取消",new OnClickListener() {
			public void onClick(DialogInterface dialog, int which) {
				// TODO Auto-generated method stub
				dialog.dismiss();
			}
		} );
		alert.show();//显示弹出框
	}

}

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="com.briup.dialog.MainActivity" >
<Button 
    android:id="@+id/btn1"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="基本弹出框"/>
  

</RelativeLayout>