Question

我传递一个stringbuild out变量来执行哪个参数类型是stringbuild，但编译器打电话给我

＆＃34;在离开功能之前，您必须为sbValue＆＃34;

指定值

    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，发布图片需要10点声望

Answer 1

[out]表示要创建。 [class]是参考类型。

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();
}

Answer 2

当将变量sb声明为StringBuilder时，必须将值传递给构造函数，否则它将初始化为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。

您可以检查here以获取StringBuilder类支持的构造函数参数的类型。

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);
}

此外，您必须从FuncOutParamString函数返回sbValue变量。

如何在StringBuilder中使用输出参数？

2 个答案: