StringBuilder.AppendFormat引发异常

Question

I have an instance of StringBuilder in my C# application wherein I would like certain lines to be padded with a varying number of spaces depending on the context. My usage is very simple:

StringBuilder MyStringBuilder = new StringBuilder();
MyStringBuilder.AppendFormat("{0:" + this._padding + "}"); // <-- Exception thrown here
MyStringBuilder.AppendLine("My data.");

If this._padding==10 , the resulting output should look something like this:

  My data. 

How can I pad my strings without resorting to using a for loop? Thanks.

ADDITIONAL INFO

Exception: "Index (zero based) must be greater than or equal to zero and less than the size of the argument list."

Answer 1

• You need to provide both the format and the arguments in one call.
• To pad left you use {0,10} , not {0:10} .

Try this:

MyStringBuilder.AppendFormat("{0," + this._padding + "}", "My Data");

There is also a string.PadLeft method that you could use.

MyStringBuilder.Append("My Data".PadLeft(this._padding));

Answer 2

您从未传递过供{0}引用的参数。

Answer 3

AppendFormat()希望将数据格式化为附加参数：

MyStringBuilder.AppendFormat("{0:" + this._padding + "}", "My data.");

Answer 4

这似乎是一种奇怪的方式：

sb.Append(' ', this._padding).AppendLine("My Data");

Answer 5

Try

//  AppendFormat("{0:" + this._padding + "}");
    AppendFormat("{0:" + this._padding + "}", "");

A place-holder is holding a place for something .

Exception: "Index (zero based) must be greater than or equal to zero and less than the size of the argument list."

0 is greater than or equal to zero but it in this case it was not less than the size of the argument list ( 0 as well).

Answer 6

You cannot simply write something like MyStringBuilder.AppendFormat("{0}"); You must give the variable to be formatted by the format string, like MyStringBuilder.AppendFormat("{0}", "My data");

Answer 7

You can use IEnumerable.Repeat to generate arbitrary numbers of the same string/char.

http://msdn.microsoft.com/en-us/library/bb348899.aspx

Answer 8

A lame way of doing it, but should work

for(int i=0; i <this._padding; i++)
{
   MyStringBuilder.AppendFormat("{0}"," ");
}

_padding needs to be an int