我通过ajax获取数据，每隔20秒查询一次数据绘制到画布上，如何自动更改TextBlock上的数据而不影响画布结构（类似于局部重绘画布）
Could you please describe in more detail about what you are trying to avoid?
The general answer is that you want to have a Binding on TextBlock.text, and that you want to call Model.setDataProperty on the bound data property.
Remember to conduct all of your changes within a single transaction.