如何组合c#谓词

本文关键字：谓词 组合 何组合 | 更新日期: 2023-09-27 18:09:08

嗨，我有两个谓词。我想知道是否有可能以某种方式将它们结合在一起?第一:

Predicate<object> viewFilter = f =>
{
    ExternalUser u = f as ExternalUser;
    return u.AgentName.ToLower().StartsWith(agentName.ToLower());
};
第二:

Predicate<object> viewFilter = f =>
{
    ExternalUser u = f as ExternalUser;
    return u.ExternalLogin.ToLower().StartsWith(login.ToLower());
};

这就是连接谓词的样子。

Predicate<object> viewFilter = f =>
{
    ExternalUser u = f as ExternalUser;
    return u.ExternalLogin.ToLower().StartsWith(login.ToLower()) && u.AgentName.ToLower().StartsWith(agentName.ToLower());
};

我需要这个WPF数据网格过滤器，其中网格源是ICollectionView。因此，在创建谓词之后，我将其设置为过滤器，如下所示:

private void FilterByLogin(ICollectionView view, string login)
{
    Predicate<object> viewFilter = f =>
    {
        ExternalUser u = f as ExternalUser;
        return u.ExternalLogin.ToLower().StartsWith(login.ToLower());
    };
    view.Filter = viewFilter;
}

如何组合c#谓词

我将创建两个新方法:

public static Prediate<object> Cast<T>(Predicate<T> inner)
{
    return new Predicate<object>(o => inner((T)o));
}
public static Predicate<T> And<T>(Predicate<T> p1, Predicate<T> p2)
{
    return x => p1(x) && p2(x);
}

则可以从谓词中删除强制转换，并将其移动到顶层:

Predicate<ExternalUser> first = u => u.AgentName.ToLower().StartsWith(agentName.ToLower());
Predicate<ExternalUser> second = u => u.ExternalLogin.ToLower().StartsWith(login.ToLower());
view.Filter = Cast(And(first, second));

真的应该像这样简单:

Predicate<object> viewFilter1 = f =>
{
    ExternalUser u = f as ExternalUser;
    return u.AgentName.ToLower().StartsWith(agentName.ToLower());
};
Predicate<object> viewFilter2 = f =>
{
    ExternalUser u = f as ExternalUser;
    return u.ExternalLogin.ToLower().StartsWith(login.ToLower());
};
Predicate<object> viewFilter = f => viewFilter1(f) && viewFilter2(f);
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