如何设置 AlertDialog.Builder 的 NegativeButton 不能点击

代码如下：

AlertDialog.Builder dialog = new AlertDialog.Builder(this);
dialog.setTitle("Dialog");

dialog.setPositiveButton("Check", new DialogInterface.OnClickListener() {
  public void onClick(DialogInterface arg0, int arg1) {
    if(condition) {
      //set NegativeButton unclickable
    } else {
      //set NegativeButton clickable
    }
  } // end of onClick
});

dialog.setNegativeButton("Cancel", new DialogInterface.OnClickListener() {
  public void onClick(DialogInterface arg0, int arg1) {
    //do something
  }
});

如何设置 NegativeButton能点击或者不能点击？

//设置点击事件
dialog.setNegativeButton("Cancel", new DialogInterface.OnClickListener() {
  public void onClick(DialogInterface arg0, int arg1) {
    //do something
  }
});
//设置点击无效
dialog.setNegativeButton("Cancel", null);