c# - 如何将对象列表存储到 ViewState

Question

我有一个 List<JobSeeker> 类型的列表.我想将它存储在 ViewState 中。如何做到这一点？

private List<JobSeeker> JobSeekersList { get; set; }

Answer 1

基本上你只需要使用 get ，然后你要么从 View 状态获取发布的数据，要么在 View 状态上第一次设置它。这是更健壮的代码，可以避免对每次调用进行所有检查(是否设置 View 状态、是否存在等)，并直接保存和使用 View 状态对象。

// using this const you avoid bugs in mispelling the correct key.
const string cJobSeekerNameConst = "JobSeeker_cnst";

public List<JobSeeker> JobSeekersList
{
    get
    {
        // check if not exist to make new (normally before the post back)
        // and at the same time check that you did not use the same viewstate for other object
        if (!(ViewState[cJobSeekerNameConst] is List<JobSeeker>))
        {
            // need to fix the memory and added to viewstate
            ViewState[cJobSeekerNameConst] = new List<JobSeeker>();
        }

        return (List<JobSeeker>)ViewState[cJobSeekerNameConst];
    }
}

避免的替代方法是

// using this const you avoid bugs in mispelling the correct key.
const string cJobSeekerNameConst = "JobSeeker_cnst";

public List<JobSeeker> JobSeekersList
{
    get
    {
        // If not on the viewstate then add it
        if (ViewState[cJobSeekerNameConst] == null)                
            ViewState[cJobSeekerNameConst] = new List<JobSeeker>();

        // this code is not exist on release, but I check to be sure that I did not 
        //  overwrite this viewstate with a different object.
        Debug.Assert(ViewState[cJobSeekerNameConst] is List<JobSeeker>);

        return (List<JobSeeker>)ViewState[cJobSeekerNameConst];
    }
}

JobSeeker 类必须是[Serializable] as

[Serializable]
public class JobSeeker
{
    public int ID;
    ...
}

并且您通常将其作为对象简单地调用，并且永远不会为空。也将在回发后返回保存的 View 状态值

JobSeekersList.add(new JobSeeker(){ID=1});
var myID = JobSeekersList[0].ID;