如何使用 StringBuilder 的输出参数？

Question

我将一个 stringbuild out 变量传递给参数类型为 out stringbuild 的函数，但编译器告诉我

"Before leave function, You must assign value to sbValue"

    public void FuncOutParamString(out StringBuilder sbValue)
    {
        sbValue.Append("wold!");
    }

    private void btnOutParam_Click(object sender, RoutedEventArgs e)
    {
        Console.WriteLine("=================== Out Parameter ===================");
        // Declare a variable but don't assign a value to it ******************************
        int y = 0;

        // Pass it in as an output parameter, even though its value is unassigned
        FuncOutParamInt(out y);

        // It's now assigned a value, so we can write it out:
        Console.WriteLine(y);

        // Declare a variable but don't assign a value to it ******************************
        StringBuilder sb = new StringBuilder();
        sb.Append("Hello ");
        FuncOutParamString(out sb);

        Console.WriteLine(sb);
    }

抱歉，我需要 10 个声望才能 post 图片

Answer 1

当将变量 sb 声明为 StringBuilder 时，您必须将一个值传递给构造函数，否则它将被初始化为 null。由于它需要从堆中分配内存，因此需要一个参数以便稍后使用追加。

您可以检查 here 构造函数参数 StringBuilder class 支持的类型。

这应该有效：

public void FuncOutParamString(StringBuilder sbValue)
{
    sbValue.Append("wold!");
    return sbValue;
}

private void btnOutParam_Click(object sender, RoutedEventArgs e)
{
    Console.WriteLine("=================== Out Parameter ===================");
    // Declare a variable but don't assign a value to it ******************************
    int y = 0;

    // Pass it in as an output parameter, even though its value is unassigned
    FuncOutParamInt(out y);

    // It's now assigned a value, so we can write it out:
    Console.WriteLine(y);

    // Declare a variable but don't assign a value to it ******************************
    StringBuilder sb = new StringBuilder(50);
    sb.Append("Hello ");
    sb = FuncOutParamString(sb);

    Console.WriteLine(sb);
}

您还必须 return 来自 FuncOutParamString 函数的 sbValue 变量。

Answer 2

[out]表示待创建。 [class] 是引用类型。

public void FuncOutParamString(StringBuilder sbValue)
{
    sbValue.Append("wold!");
}

public void FuncOutParamStringRef(ref StringBuilder sbValue)
{
    //if(...)
        sbValue = new StringBuilder();
}

public void FuncOutParamStringOut(out StringBuilder sbValue)
{
    sbValue = new StringBuilder();
}

如何使用 StringBuilder 的输出参数？

How to use output parameter with StringBuilder?

c#

wpf

out