这个是什么？

b.StringFormat = "{0:F1}";

请参阅的StringFormat 文件>也标准数字格式字符串并的自定义数字格式字符串的。

编辑：只是为了明确如何结合将创建并分配（名为假想TextBlock的文本属性正文块$在code C $ C>）

Just to make clear how a binding would be created and assigned (to the Text property of an imaginary TextBlock named textBlock) in code:

public class ViewModel
{
    public double DoubleValue { get; set; }
}

...

var viewModel = new ViewModel
{
    DoubleValue = Math.PI
};

var binding = new Binding
{
    Source = viewModel,
    Path = new PropertyPath("DoubleValue"),
    StringFormat = "{0:F1}"
};

textBlock.SetBinding(TextBlock.TextProperty, binding);

或者

var binding = new Binding
{
    Path = new PropertyPath("DoubleValue"),
    StringFormat = "{0:F1}"
};

textBlock.DataContext = viewModel;
textBlock.SetBinding(TextBlock.TextProperty, binding);