Dialog(四)——报错Unable to add window -- token null is not for an application

/**
	 * 问题描述:
	 * 创建和显示对话框的时候报错
	 * Unable to add window -- token null is not for an application
	 * 
	 * 问题修正:
	 * 不可使用Builder builder=new Builder(getApplicationContext());
	 * 应该使用Builder builder=new Builder(MainActivity.this);
	 */
	private void showDialog(){
		 Dialog dialog;
		 //正确
		 Builder builder=new Builder(MainActivity.this);
		 //错误
		 //Builder builder=new Builder(getApplicationContext());
         builder.setIcon(R.drawable.ic_launcher);
         builder.setTitle(getResources().getString(R.string.dialog_title));
         builder.setMessage(R.string.dialog_message);
         builder.setNegativeButton("取消", new DialogInterface.OnClickListener() {
				@Override
				public void onClick(DialogInterface dialog, int arg1) {
				}
			});
         builder.setPositiveButton("确定", new DialogInterface.OnClickListener() {
				@Override
				public void onClick(DialogInterface dialog, int arg1) {
				}
			});
         
         dialog=builder.create();
         dialog.show();
    }