Xamarin表单ListView缓存策略

问题描述：

我最近在Xamarin Forms应用程序中测试了CachingStrategy中ListView的列表中有1000个项目.列表项是从ViewCell数据模板创建的.我尝试对CachingStrategy使用RecycleElement选项.

I have recently tested the CachingStrategy for a ListView in a Xamarin Forms App with 1000 items in the list. List items are being created from a data template of ViewCell. I Tried using RecycleElement option for CachingStrategy.

当我使用Xamarin Profiler对在Xamarin Anroid Player(模拟器)上部署的Android App进行性能分析时，我注意到当滚动浏览列表时，内存分配不会增加(在分配摘要"选项卡上).但是，当我在模拟器上对iPhone App进行性能分析时，我注意到分配摘要"选项卡上没有显示任何数据.因此，我在滚动列表时捕获了一些快照，每当滚动列表(上下)时都会注意到，内存分配不断增加.

When I did profiling, using Xamarin Profiler, for Android App deployed on Xamarin Anroid Player (emulator) I noticed that when I scroll through the list the memory allocation doesn't increase (on allocations summary tab). But, when I did profiling for iPhone App on emulator, I noticed that no data is being displayed on Allocations Summary tab. So I captured some snapshots while scrolling through the list and noticed whenever I scroll through the list (up or down), the memory allocation keeps increasing.

为什么RecycleElement不适用于iOS(iPhone)?

Why RecycleElement is not working for iOS (iPhone)?

我正在使用Mac进行开发. 这是我的工具:

I am using Mac for development. Here are my tools:

=== Xamarin Studio ===

版本5.10.1(内部版本3) 安装UUID:7ae992a3-b710-4297-ba1d-0c519fbb2ea8 运行: 单声道4.2.1(explicit/6dd2d0d) GTK + 2.24.23(罗利主题)

Version 5.10.1 (build 3) Installation UUID: 7ae992a3-b710-4297-ba1d-0c519fbb2ea8 Runtime: Mono 4.2.1 (explicit/6dd2d0d) GTK+ 2.24.23 (Raleigh theme)

Package version: 402010102

=== Xamarin.Profiler ===

版本:0.24.0.0 位置:/Applications/Xamarin Profiler.app/Contents/MacOS/Xamarin Profiler

Version: 0.24.0.0 Location: /Applications/Xamarin Profiler.app/Contents/MacOS/Xamarin Profiler

=== Apple开发人员工具===

=== Apple Developer Tools ===

Xcode 7.1.1(9081) 版本7B1005

Xcode 7.1.1 (9081) Build 7B1005

=== Xamarin.iOS ===

版本:9.2.1.54(企业版) 哈希:eb4c1ef 分公司:硕士建立日期:2015-12-01 02:12:30-0500

Version: 9.2.1.54 (Enterprise Edition) Hash: eb4c1ef Branch: master Build date: 2015-12-01 02:12:30-0500

=== Xamarin.Android ===

版本:6.0.0.34(企业版) Android SDK:/Users/haider/Library/Developer/Xamarin/android-sdk-macosx 支持的Android版本: 4.0.3(API级别15) 4.4(API级别19) 5.0(API级别21) 5.1(API级别22) 6.0(API级别23)

Version: 6.0.0.34 (Enterprise Edition) Android SDK: /Users/haider/Library/Developer/Xamarin/android-sdk-macosx Supported Android versions: 4.0.3 (API level 15) 4.4 (API level 19) 5.0 (API level 21) 5.1 (API level 22) 6.0 (API level 23)

SDK工具版本:24.4.1 SDK平台工具版本:23.1 rc1 SDK Build Tools版本:23.0.2

SDK Tools Version: 24.4.1 SDK Platform Tools Version: 23.1 rc1 SDK Build Tools Version: 23.0.2

Java SDK:/usr Java版本"1.7.0_71" Java(TM)SE运行时环境(内部版本1.7.0_71-b14) Java HotSpot(TM)64位服务器VM(内部版本24.71-b01，混合模式)

Java SDK: /usr java version "1.7.0_71" Java(TM) SE Runtime Environment (build 1.7.0_71-b14) Java HotSpot(TM) 64-Bit Server VM (build 24.71-b01, mixed mode)

=== Xamarin Android Player ===

版本:0.6.5 位置:/Applications/Xamarin Android Player.app

Version: 0.6.5 Location: /Applications/Xamarin Android Player.app

=== Xamarin.Mac ===

版本:2.4.0.109(简化版)

Version: 2.4.0.109 (Starter Edition)

===构建信息===

=== Build Information ===

版本ID:510010003 Git修订版:f2021a209d66d49cbc0649a6d968b29040e57807 建立日期:2015-12-01 10:43:40-05 Xamarin插件:dfd4f5103e8951edbc8ac24480b53b53c55e04ff 构建通道:monodevelop-lion-cycle6-baseline

Release ID: 510010003 Git revision: f2021a209d66d49cbc0649a6d968b29040e57807 Build date: 2015-12-01 10:43:40-05 Xamarin addins: dfd4f5103e8951edbc8ac24480b53b53c55e04ff Build lane: monodevelop-lion-cycle6-baseline

===操作系统===

=== Operating System ===

Mac OS X 10.11.1 Darwin Haiders-MacBook-Pro.local 15.0.0 Darwin内核版本15.0.0 2015年9月19日星期六15:53:46 根目录:xnu-3247.10.11〜1/RELEASE_X86_64 x86_64

Mac OS X 10.11.1 Darwin Haiders-MacBook-Pro.local 15.0.0 Darwin Kernel Version 15.0.0 Sat Sep 19 15:53:46 PDT 2015 root:xnu-3247.10.11~1/RELEASE_X86_64 x86_64

答

这里有几件事要检查

在Xamarin Profiler中，确保仅在查找自定义ViewCell类，并拍摄多个快照以触发垃圾收集器.如果ViewCells的数量没有增加，则可能是导致内存泄漏的其他原因.如果ViewCells的数量在增加，请转到建议2和. 3，下面. Xamarin Profiler ViewCell示例

在ViewCell代码中，确保覆盖OnBindingContextChanged()并在OnBindingContextChanged()中而不是在ViewCell的构造函数中设置控件的属性.我在下面添加了一些示例代码，这些代码演示了如何使用自定义ViewCell来实现ListViewCachingStrategy.RecycleElement策略.

In the ViewCell code, make sure to override OnBindingContextChanged() and set the controls' properties in OnBindingContextChanged(), rather than in the ViewCell's constructor. I added some sample code below that shows how to implement the ListViewCachingStrategy.RecycleElement strategy using a custom ViewCell.

使用RecycleElement的ListView

ListView = new ListView(ListViewCachingStrategy.RecycleElement)
{
    DataTemplate(typeof(CustomViewCell))
};

ViewCell

public class CustomViewCell : ViewCell
{
    Label _myLabel;
    MenuItem _deleteAction;

    public CustomViewCell()
    {
        _myLabel = new Label();

        View = _myLabel;
    }

    protected override void OnBindingContextChanged()
    {
        base.OnBindingContextChanged();

        _myLabel.Text = "";

        var item = BindingContext as MyModel;
        if (item != null)
        {
            _myLabel.Text = item.Text;
        }
    }

    protected override void OnAppearing()
    {
        base.OnAppearing();

        //Subscribe ViewCell Event Handlers
        _deleteAction.Clicked += HandleDeleteClicked;
        ContextActions.Add(_deleteAction);
    }

    protected override void OnDisappearing()
    {
        base.OnDisappearing();

        //Unsubscribe ViewCell Event Handlers
        _deleteAction.Clicked -= HandleDeleteClicked;
        ContextActions.Remove(_deleteAction);
    }

    void HandleDeleteClicked(object sender, EventArgs e)
    {
        //Code to handle when the delete action is tapped
    }
}

ViewCell模型

public class MyModel
{
    [PrimaryKey]
    public int ID { get; set; }

    public string Text { get; set; }
}

Xamarin表单ListView缓存策略

这里有几件事要检查

使用RecycleElement的ListView

ViewCell

ViewCell模型

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