如何使用CanExecute与Mvvmcross [英] How to use CanExecute with Mvvmcross

问题描述

我有一个按钮

<Button 
      android:id="@+id/ButtonConnect"
      android:layout_width="match_parent"
      android:layout_height="wrap_content"
      android:text="Disconnect"
      local:MvxBind="{'Click':{'Path':'DisconnectCommand'}}" />

我有一个命令

public IMvxCommand DisconnectCommand
{
    get
    {
        return new MvxRelayCommand(this.GetService<IConnectionService>().Disconnect);
    }
}

然后我要启用/禁用DisconnectCommand使用

Then I want to enable/disable the DisconnectCommand using

DisconnectCommand.CanExecute(this.GetService<IConnectionService>().UsbConnected);

但是这显然是错误的（它不工作），我把支票作为参数，但通常我会做

But thats clearly wrong (It is not working), I put the check in as a a parameter, but normally I would do

DisconnectCommand.CanExecute = someBool;

但是没有属性可以设置，那么该怎么做呢？

But there is no property to set, so how to go about this?

推荐答案

要解决如何使用 CanExecute ，请查看Silverlight或WPF - 有很多在那里谈论如何使用 ICommand 的博客 - 例如 http://weblogs.asp.net /nmarun/archive/2009/12/02/using-icommand-silverlight-4.aspx 或 http://blog.galasoft.ch/archive/2009/09/26/using-relaycommands-in-silverlight-and-wpf.aspx

To work out how to use CanExecute, take a look at Silverlight or WPF - there's lots of blogs out there which talk about how to use ICommand - e.g. http://weblogs.asp.net/nmarun/archive/2009/12/02/using-icommand-silverlight-4.aspx or http://blog.galasoft.ch/archive/2009/09/26/using-relaycommands-in-silverlight-and-wpf.aspx

一个例子是：

private MvxRelayCommand _disconnectCommand;
public IMvxCommand DisconnectCommand
{
    get
    {
        if (_disconnectCommand == null)
            _disconnectCommand = new MvxRelayCommand(this.GetService<IConnectionService>().Disconnect, item => this.IsItemConnected(item));
        return _disconnectCommand;
    }
}

private void SomeServiceNotificationHandler()
{
    _disconnectCommand.RaisePropertyChanged();
}

private bool IsItemConnected(object thing)
{
    return /* your code */;
}

---

有一个小问题虽然...

---

There is one small problem though....

CanExecute 在所有平台的所有MvxBindings中并没有真正完全实现...它会为其中一些工作，但对于其中的一些，它不会 - 我现在不知道哪些！如果您遇到问题，请通过GitHub问题通知我们，他们会得到修正...

CanExecute isn't really fully implemented across all the MvxBindings across all platforms... It will work for some of them, but for some of them it won't - and I don't really know which ones at present! If you come across issues, then please let me know (via GitHub issues) and they will get fixed...

个人...我不倾向于使用 CanExecute - 我倾向于使用一个单独的布尔属性，然后我绑定到控件上的任何属性 - 例如大多数控件具有类似 Enabled ， IsEnabled ， Disabled IsDisabled 等

Personally... I don't tend to use CanExecute - I tend instead to use a separate Boolean property which I then bind to whatever property is available on the control - e.g. most controls have something like Enabled, IsEnabled, Disabled, IsDisabled, etc.

我通常发现设置布尔属性更容易（更可读），而不是调用 RaiseCanExecuteChanged

I generally find it easier (and more readable) to set the Boolean property rather than to call RaiseCanExecuteChanged

eg我会使用以下东西：

e.g. I'd use something like:

<Button 
  android:id="@+id/ButtonConnect"
  android:layout_width="match_parent"
  android:layout_height="wrap_content"
  android:text="Disconnect"
  local:MvxBind="{'Click':{'Path':'DisconnectCommand'},'Enabled':{'Path':'UsbConnected'}}" />

你可以肯定地认为 CanExecute 具有优点 - 因为它将Command逻辑全部保存在一个对象中，并且因为它可以用于阻止 RelayCommand 执行调用c $ c>。这就是为什么我很高兴在我们找到它们时，尝试修复mvvmcross绑定中的 CanExecute 错误。

You can definitely argue that the CanExecute approach has advantages - because it keeps the Command logic all in one object, and because it can be used to prevent Execute calls happening within the RelayCommand. That's why I'm happy to try to fix CanExecute bugs in mvvmcross bindings as we find them.

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