[英]"mismatched types expected unit type `()` found enum `Option<String>`" Error when trying to read the content of a file with Tauri
I was trying to use the file picker of tauri to read the contents of a file in Rust this way.我试图使用 tauri 的文件选择器以这种方式读取 Rust 中文件的内容。
fn open_file() -> Option<String> {
let dialog_open_file = tauri::api::dialog::FileDialogBuilder::new();
dialog_open_file.pick_file(|path| {
match path {
Some(directory) => {
let archivo = fs::read_to_string(directory);
match archivo {
Ok(content) => { return Some(content); },
Err(error) => { return None; }
}
},
None => { return None; }
}
});
}
The problem is that when I try to return Some(content) I get the error "mismatched types expected unit type ()
found enum Option<String>
"问题是,当我尝试返回 Some(content) 时,我收到错误“mismatched types expected unit type
()
found enum Option<String>
”
error[E0308]: mismatched types
--> src/main.rs:25:43
|
25 | Ok(content) => { return Some(content); },
| ^^^^^^^^^^^^^ expected `()`, found enum
= note: expected unit type `()`
found enum `Option<String>`
error[E0308]: mismatched types
--> src/main.rs:18:19
|
18 | fn open_file() -> Option<String> {
| --------- ^^^^^^^^^^^^^^ expected enum `Option`, found `()`
| |
| implicitly returns `()` as its body has no tail or `return` expression
|
= note: expected enum `Option<String>`
found unit type `()`
I have tried many ways but I can't return the Option out of the function "dialog_open_file" to make the function return something.我尝试了很多方法,但我无法从函数“dialog_open_file”中返回选项以使函数返回一些东西。
It looks like tauri
has changed its API in this area.看起来
tauri
在这方面改变了它的 API。 See https://docs.rs/tauri-api/0.7.6/tauri_api/dialog/index.html .请参阅https://docs.rs/tauri-api/0.7.6/tauri_api/dialog/index.html 。 Now the functions no longer accept a closure, but instead return a
dialog::Response
struct.现在这些函数不再接受闭包,而是返回一个
dialog::Response
结构。
This means your code could be written as something like:这意味着您的代码可以编写为:
// This is tauri's internal error type too.
use anyhow::{Error, bail};
fn open_file_impl() -> Result<String, Error> {
use tauri::api::dialog::Response;
let result = tauri::api::dialog::select(None,None)?;
let path = match {
Response::Okay(s) => s;
Response::OkayMultiple(s) => bail!("multiple selected"),
Response::Cancel => bail!("canceled");
}
Ok(fs::read_to_string(directory)?)
}
pub fn open_file() -> Option<String> {
open_file_impl().ok()
}
I'd probably introduce a concrete error type with this, rather than relying on anyhow
... but that does make things longer.我可能会为此引入一个具体的错误类型,而不是
anyhow
都依赖......但这确实会使事情变得更长。
Or you could get rid of the open_file_impl
altogether...或者你可以完全摆脱
open_file_impl
...
fn open_file_impl() -> Option<String> {
use tauri::api::dialog::Response;
let result = tauri::api::dialog::select(None,None).ok()?;
if let Response::Okay(path) = result {
fs::read_to_string(directory).ok()
} else {
None
}
}
This post does not work for the OP question, because tauri's API requires the closure to be 'static
, and thus rules out the possibility (except with dirty unsafe
hacks) to retrieve the content of the file in a way similar to what was asked.这篇文章不适用于 OP 问题,因为 tauri 的 API 要求闭包是
'static
,因此排除了以类似于所要求的方式检索文件内容的可能性(除了肮脏的unsafe
黑客)。
Also, tauri's API has been changed in more recent versions.此外,tauri 的 API 在最近的版本中已更改。 If you are only interested in a solution that specifically works with tauri, please see @Michael Anderson's answer.
如果您只对专门适用于 tauri 的解决方案感兴趣,请参阅@Michael Anderson 的回答。
As you can see, there are two errors, which are opposite, in some way: one error tells you that Rust expected ()
, but found Option<String>
, and the other one that it expected Option<String>
, but found ()
.正如你所看到的,有两个错误,在某种程度上是相反的:一个错误告诉你 Rust 期望
()
,但是找到了Option<String>
,另一个错误告诉你它期望Option<String>
,但是找到了()
. This should prompt you to check if you are passing you Option<String>
at the right place and, in fact, you're not.这应该会提示您检查是否在正确的位置传递
Option<String>
,事实上,您不是。
A closure is a function (not quite the same as other functions you define with fn
, but still a function), so when you call return
in it, you're actually returning inside the closure.闭包是一个函数(与您使用
fn
定义的其他函数不完全相同,但仍然是一个函数),因此当您在其中调用return
时,您实际上是在闭包内部返回。 So, the error just comes from the fact that pick_file
expected a function that returns ()
, whereas you provided one that returns Option<String>
, and conversely the outer function is (implicitly) returning ()
.因此,错误只是来自这样一个事实,即
pick_file
期望一个返回()
的函数,而您提供了一个返回Option<String>
的函数,相反,外部函数是(隐式)返回()
。
You may ask: is there a way to return from inside the closure, but for the return statement to apply to the outside function, and the answer is no , so one way would be to create a variable outside and mutate it from inside the closure:你可能会问:有没有办法从闭包内部返回,但是 return 语句应用于外部函数,答案是否定的,所以一种方法是在外部创建一个变量并从闭包内部对其进行变异:
fn open_file() -> Option<String> {
let dialog_open_file = tauri::api::dialog::FileDialogBuilder::new();
let mut result = None;
dialog_open_file.pick_file(|path| {
if let Some(directory) = path {
let archivo = fs::read_to_string(directory);
if let Ok(content) = archivo {
result = Some(content);
}
}
});
result
}
If you format your code, you would find out that you are missing the return statement in the outer space.如果你格式化你的代码,你会发现你错过了外层空间的 return 语句。
fn open_file() -> Option<String> {
let dialog_open_file = tauri::api::dialog::FileDialogBuilder::new();
let mut result = None;
dialog_open_file.pick_file(|path| match path {
Some(directory) => {
let archivo = fs::read_to_string(directory);
match archivo {
Ok(content) => result = Some(content),
Err(error) => result = None,
}
}
});
result
}
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