lenn
/
dioxus-mirror
镜像来自 https://github.com/DioxusLabs/dioxus.git


			
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                        <h1 id="error-handling"><a class="header" href="#error-handling">Error handling</a></h1>
<p>A selling point of Rust for web development is the reliability of always knowing where errors can occur and being forced to handle them</p>
<p>However, we haven't talked about error handling at all in this guide! In this chapter, we'll cover some strategies in handling errors to ensure your app never crashes.</p>
<h2 id="the-simplest--returning-none"><a class="header" href="#the-simplest--returning-none">The simplest – returning None</a></h2>
<p>Astute observers might have noticed that <code>Element</code> is actually a type alias for <code>Option&lt;VNode&gt;</code>. You don't need to know what a <code>VNode</code> is, but it's important to recognize that we could actually return nothing at all:</p>
<pre><pre class="playground"><code class="language-rust edition2018">
<span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>fn App(cx: Scope) -&gt; Element {
    None
}
<span class="boring">}
</span></code></pre></pre>
<p>This lets us add in some syntactic sugar for operations we think <em>shouldn't</em> fail, but we're still not confident enough to &quot;unwrap&quot; on.</p>
<blockquote>
<p>The nature of <code>Option&lt;VNode&gt;</code> might change in the future as the <code>try</code> trait gets upgraded.</p>
</blockquote>
<pre><pre class="playground"><code class="language-rust edition2018">
<span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>fn App(cx: Scope) -&gt; Element {
    // immediately return &quot;None&quot;
    let name = cx.use_hook(|_| Some(&quot;hi&quot;))?;
}
<span class="boring">}
</span></code></pre></pre>
<h2 id="early-return-on-result"><a class="header" href="#early-return-on-result">Early return on result</a></h2>
<p>Because Rust can't accept both Options and Results with the existing try infrastructure, you'll need to manually handle Results. This can be done by converting them into Options or by explicitly handling them.</p>
<pre><pre class="playground"><code class="language-rust edition2018">
<span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>fn App(cx: Scope) -&gt; Element {
    // Convert Result to Option
    let name = cx.use_hook(|_| &quot;1.234&quot;).parse().ok()?;


    // Early return
    let count = cx.use_hook(|_| &quot;1.234&quot;);
    let val = match count.parse() {
        Ok(val) =&gt; val
        Err(err) =&gt; return cx.render(rsx!{ &quot;Parsing failed&quot; })
    };
}
<span class="boring">}
</span></code></pre></pre>
<p>Notice that while hooks in Dioxus do not like being called in conditionals or loops, they <em>are</em> okay with early returns. Returning an error state early is a completely valid way of handling errors.</p>
<h2 id="match-results"><a class="header" href="#match-results">Match results</a></h2>
<p>The next &quot;best&quot; way of handling errors in Dioxus is to match on the error locally. This is the most robust way of handling errors, though it doesn't scale to architectures beyond a single component.</p>
<p>To do this, we simply have an error state built into our component:</p>
<pre><pre class="playground"><code class="language-rust edition2018">
<span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>let err = use_state(cx, || None);
<span class="boring">}
</span></code></pre></pre>
<p>Whenever we perform an action that generates an error, we'll set that error state. We can then match on the error in a number of ways (early return, return Element, etc).</p>
<pre><pre class="playground"><code class="language-rust edition2018">
<span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>fn Commandline(cx: Scope) -&gt; Element {
    let error = use_state(cx, || None);

    cx.render(match *error {
        Some(error) =&gt; rsx!(
            h1 { &quot;An error occured&quot; }
        )
        None =&gt; rsx!(
            input {
                oninput: move |_| error.set(Some(&quot;bad thing happened!&quot;)),
            }
        )
    })
}
<span class="boring">}
</span></code></pre></pre>
<h2 id="passing-error-states-through-components"><a class="header" href="#passing-error-states-through-components">Passing error states through components</a></h2>
<p>If you're dealing with a handful of components with minimal nesting, you can just pass the error handle into child components.</p>
<pre><pre class="playground"><code class="language-rust edition2018">
<span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>fn Commandline(cx: Scope) -&gt; Element {
    let error = use_state(cx, || None);

    if let Some(error) = **error {
        return cx.render(rsx!{ &quot;An error occured&quot; });
    }

    cx.render(rsx!{
        Child { error: error.clone() }
        Child { error: error.clone() }
        Child { error: error.clone() }
        Child { error: error.clone() }
    })
}
<span class="boring">}
</span></code></pre></pre>
<p>Much like before, our child components can manually set the error during their own actions. The advantage to this pattern is that we can easily isolate error states to a few components at a time, making our app more predictable and robust.</p>
<h2 id="going-global"><a class="header" href="#going-global">Going global</a></h2>
<p>A strategy for handling cascaded errors in larger apps is through signaling an error using global state. This particular pattern involves creating an &quot;error&quot; context, and then setting it wherever relevant. This particular method is not as &quot;sophisticated&quot; as React's error boundary, but it is more fitting for Rust.</p>
<p>To get started, consider using a built-in hook like <code>use_context</code> and <code>use_context_provider</code> or Fermi. Of course, it's pretty easy to roll your own hook too.</p>
<p>At the &quot;top&quot; of our architecture, we're going to want to explicitly declare a value that could be an error.</p>
<pre><pre class="playground"><code class="language-rust edition2018">
<span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>enum InputError {
    None,
    TooLong,
    TooShort,
}

static INPUT_ERROR: Atom&lt;InputError&gt; = |_| InputError::None;
<span class="boring">}
</span></code></pre></pre>
<p>Then, in our top level component, we want to explicitly handle the possible error state for this part of the tree.</p>
<pre><pre class="playground"><code class="language-rust edition2018">
<span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>fn TopLevel(cx: Scope) -&gt; Element {
    let error = use_read(cx, INPUT_ERROR);

    match error {
        TooLong =&gt; return cx.render(rsx!{ &quot;FAILED: Too long!&quot; }),
        TooShort =&gt; return cx.render(rsx!{ &quot;FAILED: Too Short!&quot; }),
        _ =&gt; {}
    }
}
<span class="boring">}
</span></code></pre></pre>
<p>Now, whenever a downstream component has an error in its actions, it can simply just set its own error state:</p>
<pre><pre class="playground"><code class="language-rust edition2018">
<span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>fn Commandline(cx: Scope) -&gt; Element {
    let set_error = use_set(cx, INPUT_ERROR);

    cx.render(rsx!{
        input {
            oninput: move |evt| {
                if evt.value.len() &gt; 20 {
                    set_error(InputError::TooLong);
                }
            }
        }
    })
}
<span class="boring">}
</span></code></pre></pre>
<p>This approach to error handling is best in apps that have &quot;well defined&quot; error states. Consider using a crate like <code>thiserror</code> or <code>anyhow</code> to simplify the generation of the error types.</p>
<p>This pattern is widely popular in many contexts and is particularly helpful whenever your code generates a non-recoverable error. You can gracefully capture these &quot;global&quot; error states without panicking or mucking up state.</p>

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