我有一个问题。我正在尝试与Mi Band接口。在github上找到这段代码,效果很好。但是,我不明白数据类型转换发生了什么。
var u16 = UnsafePointer<Int32>(characteristic.value!.bytes).memory
来自此代码块:
func peripheral(peripheral: CBPeripheral, didUpdateValueForCharacteristic characteristic: CBCharacteristic, error: NSError?) {
output("Data for "+characteristic.UUID.UUIDString, data: characteristic.value!)
if(characteristic.UUID.UUIDString == "FF06") {
spinnerView.hidden = true
let u16 = UnsafePointer<Int>(characteristic.value!.bytes).memory
stepsView.stringValue = ("\(u16) steps")
} else if(characteristic.UUID.UUIDString == "FF0C") {
spinnerView.hidden = true
var u16 = UnsafePointer<Int32>(characteristic.value!.bytes).memory
u16 = u16 & 0xff
batteryView.stringValue = ("\(u16) % charged")
}
}
有人可以向我解释一下吗?谢谢!
答案 0 :(得分:0)
此部分获取内存中的地址:
characteristic.value!.bytes
但.bytes
的返回类型为UnsafePointer<Void>
,因此将其转换为UnsafePointer<Int32>
类型,即Swift等效于指向32位整数的C指针(int32_t* ptr;
)。
UnsafePointer<Int32>(characteristic.value!.bytes)
在Swift中,您可以使用.memory
获取此类指针的内容(在C中它将是*ptr
)。因此u16
变量是类型Int32
的值(该内存位置的内容,解释为Int32
)。
var u16 = UnsafePointer<Int32>(characteristic.value!.bytes).memory
下一行屏蔽所有高24位,只留下该值的最低8位,然后将其打印为电池百分比。
答案 1 :(得分:0)
Swift 3
if you have this kind of characteristic :
<CBCharacteristic: 0x26e42b42, UUID = Battery, properties = 0x33,
value = <4d455348 54454348 204153>, notifying = NO>
then use this type code:
let value = [UInt8](characteristic.value!)