我正在学习Rx for .NET,一位同事给我发了一个简单的例子,但有一些我不喜欢的丑陋。
代码:
using System;
using System.Reactive.Linq;
using System.Reactive.Threading.Tasks;
using System.Threading.Tasks;
using System.Windows.Forms;
using System.Collections.Generic;
namespace WindowsFormsApplication1
{
public partial class Form1 : Form
{
public IObservable<Content> contentStream;
public static bool isRunning = false;
public Form1()
{
InitializeComponent();
contentStream = Observable.FromEventPattern<ScrollEventArgs>(dataGridView1, "Scroll") // create scroll event observable
.Where(e => (dataGridView1.Rows.Count - e.EventArgs.NewValue < 50 && !isRunning)) //discart event if scroll is not down enough
//or we are already retrieving items (isRunning)
.Select(e => { isRunning = true; return 100; }) //transform to 100--100--100--> stream, discart next events until we finish
.Scan((x, y) => x + y) //get item index by accumulating stream items
.StartWith(0) //start with 0 before event gets triggered
.SelectMany(i => getContent(i).ToObservable());//create a stream with the result of an async function and merge them into just one stream
contentStream.Subscribe(c => invokeUpdateList(c)); //just update the control every time a item is in the contentStream
}
async private Task<Content> getContent(int index)
{
await Task.Delay(1000);//request to a web api...
return new Content(index);//mock the response
}
private void invokeUpdateList(Content c)
{
dataGridView1.Invoke((MethodInvoker)delegate
{
updateList(c);
});
}
private void updateList(Content c)
{
foreach (var item in c.pageContent)
{
dataGridView1.Rows.Add(item);
}
isRunning = false; //unlocks event filter
}
}
public class Content
{
public List<string> pageContent = new List<string>();
public const string content_template = "This is the item {0}.";
public Content()
{
}
public Content(int index)
{
for (int i = index; i < index + 100; i++)
{
pageContent.Add(string.Format(content_template, i));
}
}
}
}
我不喜欢的是isRunning
过滤器。有没有更好的方法来放弃流中的某些事件,直到控件更新为止?
虽然@Shlomo方法似乎是正确的但它不会在加载时开始填充:
var index = new BehaviorSubject<int>(0);
var source = Observable.FromEventPattern<ScrollEventArgs>(dataGridView2, "Scroll")
.Where(e => dataGridView2.Rows.Count - e.EventArgs.NewValue < 50)
.Select(_ => Unit.Default)
.StartWith(Unit.Default)
.Do(i => Console.WriteLine("Event triggered"));
var fetchStream = source
.WithLatestFrom(index, (u, i) => new {unit = u,index = i } )
.Do(o => Console.WriteLine("Merge result" + o.unit + o.index ))
.DistinctUntilChanged()
.Do(o => Console.WriteLine("Merge changed" + o.unit + o.index))
.SelectMany(i => getContent(i.index).ToObservable());
var contentStream = fetchStream.WithLatestFrom(index, (c, i) => new { Content = c, Index = i })
.ObserveOn(dataGridView2)
.Subscribe(a =>
{
updateGrid(a.Content);
index.OnNext(a.Index + 100);
});
我可以在输出日志中看到“事件已触发”,但在我进入source
后,第一个StartWith(Unit.Default)
元素(WithLatestFrom
)似乎丢失了。
答案 0 :(得分:1)
这看起来像某种分页自动滚动实现?从概念上讲,它可以帮助你分割你的观察力:
var index = new BehaviorSubject<int>(0);
var source = Observable.FromEventPattern<ScrollEventArgs>(dataGridView1, "Scroll")
.Where(e => dataGridView1.Rows.Count - e.EventArgs.NewValue < 50)
.Select(_ => Unit.Default)
.StartWith(Unit.Default);
var fetchStream = source
.WithLatestFrom(index, (_, i) => i)
.DistinctUntilChanged()
.SelectMany(i => getContent(i).ToObservable());
所以source
是一系列单位,基本上是用户想要发起列表更新的空通知。 index
表示下载的下一个索引。 fetchstream
将source
与index
合并以确保对给定索引只有一个请求,然后启动提取。
现在我们有一系列不同的请求,我们需要订阅和更新用户界面index
。
var contentStream =
fetchStream .WithLatestFrom(index, (c, i) => new { Content = c, Index = i })
.ObserveOn(dataGridView1)
.Subscribe(a =>
{
updateList(a.Content);
index.OnNext(a.Index + 100);
});
注意ObserveOn(datagridView1)
完成与InvokeUpdateList
方法相同的操作,但是更简洁(需要Nuget System.Reactive.Windows.Forms
),因此您可以删除该方法。
所有这些都可以在构造函数中进行,因此您可以隐藏其中的所有状态更改。