如何在Android应用中使用AlertDialog实现一个对话框

AlertDialog.Builder builder = new AlertDialog.Builder(this);   builder.setTitle("确认对话框");   builder.setIcon(R.drawable.icon_72);   builder.setMessage("这里是对话框内容");   builder.setPositiveButton("确定", new DialogInterface.OnClickListener() {    @Override    public void onClick(DialogInterface arg0, int arg1) {     // TODO Auto-generated method stub     Toast.makeText(AlertDialog_text.this, "点击了确定按钮", 1).show();    }   });   AlertDialog dialog = builder.create();   dialog.show(); //显示、