设计界面布局时显示的错误：

Rendering Problems Missing styles. Is the correct theme chosen for this layout?
Use the Theme combo box above the layout to choose a different layout, or fix the theme style references.
Failed to find style ‘buttonStyle’ in current theme (8 similar errors not shown)

预览时控件非常小，如图：

解决办法：

在界面预览状态，点击上面的“AppTheme”，在打开的对话框中选择一种风格即可。