我正在尝试通过Rust中的CGWindowListCopyWindowInfo获取窗口所有者名称。到目前为止，我已经成功获取了CFDictionaryRef，但是我无法为CFDictionaryGetValueIfPresent使用正确的指针。
const options: CGWindowListOption = kCGWindowListOptionOnScreenOnly + kCGWindowListExcludeDesktopElements;
const ptr_window_list_info: CFArrayRef = unsafe { CGWindowListCopyWindowInfo(options, kCGNullWindowID) as CFArrayRef };
const count = unsafe { CFArrayGetCount(ptr_window_list_info) };
for i in 0..count-1 {
let dic_ref = CFArrayGetValueAtIndex(ptr_window_list_info, i) as CFDictionaryRef;
//let key = CFString::new("kCGWindowOwnerName");
let b = CFDictionaryGetValueIfPresent(dic_ref, ?, ?);
println!("window owner name: {}", value);
}
我对Rust还是陌生的，将不胜感激。
CFDictionaryGetValueIfPresent看起来像这样：
Boolean CFDictionaryGetValueIfPresent(CFDictionaryRef theDict, const void *key, const void **value);
在core_foundation中，看起来像这样：
pub unsafe extern "C" fn CFDictionaryGetValueIfPresent(
theDict: CFDictionaryRef,
key: *const c_void,
value: *mut *const c_void
) -> Boolean
我相信密钥希望是CFStringRef；在C语言中，有一个宏可以简化操作（CFSTR("cstring")），在这里我们必须使用稍长的形式：
let c_key = CString::new("kCGWindowOwnerName").unwrap();
let cf_key = unsafe {
CFStringCreateWithCString(std::ptr::null(), c_key.as_ptr(), kCFStringEncodingUTF8)
};
这给我们CFStringRef，在core_foundation中是这样定义的：
pub type CFStringRef = *const __CFString;
它已经是*const指针，但不是我们需要的类型。您可以改为c_void：
let key_ptr: *const c_void = unsafe { std::mem::transmute(cf_key) };
value参数只需要一个原始双指针来存储结果。创建一个空指针：
let mut value: *const c_void = std::ptr::null();
并传递可变的引用给它（&mut value）以得到*mut *const c_void。
您的rust代码中有一些错误和奇怪之处。这是一个经过评论的有效示例：
use core_graphics::display::*;
use core_foundation::string::*;
use std::ffi::{ CStr, CString, c_void };
fn main() {
// CGWindowListOption is a bitmask, combine the flags with bitwise OR
const OPTIONS: CGWindowListOption = kCGWindowListOptionOnScreenOnly | kCGWindowListExcludeDesktopElements;
// No need to specify the type or use 'as'; CFArrayRef is the return type from CGWindowListCopyWindowInfo
let window_list_info = unsafe { CGWindowListCopyWindowInfo(OPTIONS, kCGNullWindowID) };
// Don't use const here, CFArrayGetCount returns CFIndex (long)
let count: i64 = unsafe { CFArrayGetCount(window_list_info) };
for i in 0..count-1 {
// Here we need the 'as', CFArrayGetValueAtIndex just returns void*
let dic_ref = unsafe { CFArrayGetValueAtIndex(window_list_info, i) as CFDictionaryRef };
// Create a CString from the key name we are interested in
let c_key = CString::new("kCGWindowOwnerName").unwrap();
// Create a CFString, needs to be released with `CFRelease`. I leave that as an exercise for the reader.
let cf_key = unsafe { CFStringCreateWithCString(std::ptr::null(), c_key.as_ptr(), kCFStringEncodingUTF8) };
// cf_key is a CFStringRef, which is a type alias to *const __CFString
// We transmute it into *const c_void since that is what CFDictionaryGetValueIfPresent wants
let key_ptr: *const c_void = unsafe { std::mem::transmute(cf_key) };
// A raw void* to hold the result
let mut value: *const c_void = std::ptr::null();
if unsafe { CFDictionaryGetValueIfPresent(dic_ref, key_ptr, &mut value) != 0 } {
// CFDictionaryGetValueIfPresent returned true; that means value must point to a CFStringRef
let cf_ref = value as core_foundation::string::CFStringRef;
// Get a pointer to a C-string buffer with the characters from the CFString
let c_ptr = unsafe { CFStringGetCStringPtr(cf_ref, kCFStringEncodingUTF8) };
// The value may be null; don't pass it to CStr::from_ptr
if c_ptr.is_null() { continue; }
// Wrap the pointer in a rust CStr so we can convert a str
let c_value = unsafe { CStr::from_ptr(c_ptr) };
println!("{}", c_value.to_str().unwrap());
}
}
}
供参考，这是C中的相同示例：
#import <Foundation/Foundation.h>
#import <CoreGraphics/CoreGraphics.h>
int main(int argc, const char * argv[]) {
@autoreleasepool {
CGWindowListOption options = kCGWindowListOptionOnScreenOnly | kCGWindowListExcludeDesktopElements;
CFArrayRef windows = CGWindowListCopyWindowInfo(options, kCGNullWindowID);
CFIndex count = CFArrayGetCount(windows);
for (int i = 0; i < count; i++)
{
CFDictionaryRef windowDict = CFArrayGetValueAtIndex(windows, i);
CFStringRef key = CFStringCreateWithCString(NULL, "kCGWindowOwnerName", kCFStringEncodingUTF8);
const void* value = nil;
if (CFDictionaryGetValueIfPresent(windowDict, key, &value) == YES)
{
const char* c_value = CFStringGetCStringPtr(value, kCFStringEncodingUTF8);
NSLog(@"window: %s", c_value);
}
CFRelease(key);
}
}
return 0;
}
Disclaimer我也对锈病还比较陌生，这可能不是惯用的解决方法
除了TheNextman的答案外，我还修改了代码，以避免使用transmute。
use core_graphics::display::*;
use core_foundation::string::*;
use core_foundation::number::*;
use core_foundation::base::*;
use std::ffi::{ CStr, c_void };
fn main() {
const OPTIONS: CGWindowListOption = kCGWindowListOptionOnScreenOnly | kCGWindowListExcludeDesktopElements;
let window_list_info = unsafe { CGWindowListCopyWindowInfo(OPTIONS, kCGNullWindowID) };
let count = unsafe { CFArrayGetCount(window_list_info) };
for i in 0..count {
let dic_ref = unsafe { CFArrayGetValueAtIndex(window_list_info, i as isize) as CFDictionaryRef };
let key = CFString::new("kCGWindowOwnerName");
let mut value: *const c_void = std::ptr::null();
if unsafe { CFDictionaryGetValueIfPresent(dic_ref, key.to_void(), &mut value) != 0 } {
let cf_ref = value as CFStringRef;
let c_ptr = unsafe { CFStringGetCStringPtr(cf_ref, kCFStringEncodingUTF8) };
if !c_ptr.is_null() {
let c_result = unsafe { CStr::from_ptr(c_ptr) };
let result = String::from(c_result.to_str().unwrap());
println!("window owner name: {}", result)
}
}
}
unsafe {
CFRelease(window_list_info as CFTypeRef)
}
}