UniDeskExpr Type

Expression engine singleton that supports %variable syntax for system data references and %{math expression} syntax for numerical computations in text. All text controls (e.g. UDCText) call convertStr() before rendering.

Item	Description
Control Type	Global Singleton (QML_SINGLETON)
Source File	UniDesk/CppExt/UniDeskExpr.h / .cpp
Inherits	QQuickItem
QML Import	import UniDesk 1.0

Properties

readonly property SystemStats systemStats

Cached system stats, updated every second by an internal timer. The SystemStats struct contains:

• cpu.usagePercent / cpu.temperature — CPU usage and temperature
• cpu.name / cpu.physicalCores / cpu.logicalCores / cpu.maxClockMHz — CPU model and specs
• gpu.name / gpu.usagePercent / gpu.vramTotal / gpu.vramUsed / gpu.temperature — GPU info
• mem.virtmemTotal / mem.virtmemUsed / mem.virtmemPercent — Physical memory
• mem.swapmemTotal / mem.swapmemUsed / mem.swapmemPercent — Swap memory
• net.bytesSend / net.bytesRecv — Total network traffic
• net.bytesSendPerSec / net.bytesRecvPerSec — Network rate per second
• net.dropPercent — Packet drop rate
• bat.batteryPercent / bat.charging / bat.remainMinutes — Battery info
• disk.totalSpace / disk.freeSpace / disk.usagePercent — Disk info
• sysInfo.uptimeSeconds / sysInfo.hostname / sysInfo.osName — System info
• sysInfo.screenWidth / sysInfo.screenHeight — Screen resolution

Methods

function convertStr(text, presets) → QString

Parses all %variable and %{math expression} tokens in the text and replaces them with actual values.

Replacement priority:

1. All %variable tokens (system data, date/time) are replaced directly via QString::replace
2. Then %{math expression} blocks are evaluated with the exprtk library, with custom variables from presets

import UniDesk 1.0

// %variable replacement
var result = UniDeskExpr.convertStr("CPU: %cpuPercent%")
// → "CPU: 23.5%"

// %{math expression} evaluation (system variables still need % prefix inside)
var result = UniDeskExpr.convertStr(
    "Speed: %{%bytesRecvPerSec/1024} KB/s"
)
// → "Speed: 512.5 KB/s"

// Custom variables via presets (no % prefix needed)
var result = UniDeskExpr.convertStr(
    "Total: %{a + b}",
    { "a": 10, "b": 20 }
)
// → "Total: 30"

function evalResponse(response, expression) → QVariant

Parses an API response (JSON string) and evaluates a JS expression in the response global object context, supporting dictionary and list access.

var value = UniDeskExpr.evalResponse(
    '{"temp": 26.5, "weather": {"city": "Beijing"}}',
    "weather.city"
)
// → "Beijing"

function stopTimer()

Stops the internal data refresh timer (typically called on application exit).

%variable Replacement Table

All %variable tokens are matched and replaced directly via QString::replace, executed in order — earlier matches take priority.

CPU

Variable	Description	Type
%cpuPercent	CPU usage	double (%)
%cpuTemp	CPU temperature	double (°C)
%cpuName	CPU model name	string
%cpuCores	CPU logical core count (threads)	int
%cpuMaxClock	CPU max clock speed	double (MHz)

GPU

Variable	Description	Type
%gpuUsagePercent	GPU usage	double (%)
%gpuVramTotal	GPU total VRAM	uint64 (bytes)
%gpuVramUsed	GPU used VRAM	uint64 (bytes)
%gpuTemp	GPU temperature	double (°C)
%gpuName	GPU model name	string

Memory

Variable	Description	Type
%virtmemTotal	Total physical memory	uint64 (bytes)
%virtmemUsed	Used physical memory	uint64 (bytes)
%virtmemPercent	Physical memory usage	double (%)
%swapmemTotal	Total swap memory	uint64 (bytes)
%swapmemUsed	Used swap memory	uint64 (bytes)
%swapmemPercent	Swap memory usage	double (%)

Network

Variable	Description	Type
%bytesSendTotal	Total bytes sent	uint64
%bytesRecvTotal	Total bytes received	uint64
%bytesSendPerSec	Bytes sent per second	uint64
%bytesRecvPerSec	Bytes received per second	uint64
%dropPercent	Packet drop rate	double (%)

Battery

Variable	Description	Type
%bpercent	Battery percentage	int
%bplug	Currently charging (1/0)	int
%bleftdays	Days remaining (UNLIMITED when charging)	string
%blefthours	Hours remaining (UNLIMITED when charging)	string
%bleftmins	Minutes remaining (UNLIMITED when charging)	string
%blefthoursr	Hours remaining (excluding days)	string
%bleftminsr	Minutes remaining (excluding hours)	string

Disk

Variable	Description	Type
%diskTotal	System drive total space	uint64 (bytes)
%diskFree	System drive free space	uint64 (bytes)
%diskPercent	System drive usage	double (%)

System

Variable	Description	Type
%uptime	System uptime	quint64 (seconds)
%hostname	Host name	string
%osName	Operating system name	string
%screenWidth	Primary screen width	int (pixels)
%screenHeight	Primary screen height	int (pixels)

Date & Time

Variable	Description	Example
%yyyy	4-digit year	2026
%yy	2-digit year	26
%MMMM	Full month name	August
%MMM	Abbreviated month	Aug
%MM	2-digit month	08
%M	Month	8
%dddd	Full day name	Saturday
%ddd	Abbreviated day	Sat
%dd	2-digit day	22
%d	Day	22
%HH	2-digit hour (24h)	14
%hh	2-digit hour (12h)	02
%H	Hour (24h)	14
%h	Hour (12h)	2
%mm	2-digit minute	35
%m	Minute	35
%ss	2-digit second	59
%s	Second	59
%ap	Lowercase am/pm	am / pm
%AP	Uppercase AM/PM	AM / PM
%zzz	3-digit milliseconds	123
%z	Milliseconds	123
%t	Timestamp	1756878959

Calendar

Variable	Description	Type
%isLeapYear	Leap year (1/0)	int
%yearDays	Days in current year	int
%monthDays	Days in current month	int
%dayOfYear	Day of year	int
%dayOfWeek	Day of week (1=Monday)	int

%{math expression} Blocks

%{...} supports exprtk math expression syntax. Execution flow:

1. All %variable tokens (including those inside %{}) are replaced with their actual numeric values
2. The content inside %{...} is then evaluated as a math expression

Therefore, when referencing system variables inside %{}, you must keep the % prefix (e.g. %{%cpuPercent * 2}).

Custom variables passed via presets do not need a % prefix — use them directly by name.

Supports:

• Arithmetic: + - * / ^
• Math functions: sin cos sqrt abs log exp min max etc.
• Comparison: > < >= <= == !=
• Nested parentheses

// Unit conversion (system variables need % prefix, substituted before evaluation)
"%{%bytesRecvPerSec/1048576} MB/s"

// Percentage calculation
"%{%virtmemUsed/%virtmemTotal*100}%"

// CPU temperature to Fahrenheit
"%{%cpuTemp * 9 / 5 + 32}°F"

// GPU VRAM usage percentage
"%{%gpuVramUsed / %gpuVramTotal * 100}%"

// Using preset variables (no % prefix)
UniDeskExpr.convertStr("%{price * count}", { "price": 9.9, "count": 3 })
// → "29.7"

// Mixed usage
UniDeskExpr.convertStr("%{%cpuPercent + bonus}", { "bonus": 5 })
// → "28.5"

Full Example

import UniDesk 1.0
import UniDesk.Controls 1.0

UDCText {
    textContent: "CPU: %cpuPercent%  GPU: %gpuUsagePercent%  Memory: %virtmemPercent%"
}

UDCText {
    textContent: "CPU Temp: %cpuTemp°C  GPU Temp: %gpuTemp°C"
}

UDCText {
    textContent: "GPU: %gpuName  VRAM: %{%gpuVramUsed/1048576}MB"
}

UDCText {
    textContent: "Network: %{%bytesRecvPerSec/1048576} MB/s  Disk: %diskPercent%"
}

UDCText {
    textContent: "%osName | %hostname | Uptime: %uptime seconds"
}

Implementation Details

• System data is refreshed by an internal 1000ms (1 second) timer.
• % variables use QString::replace for direct substitution — no escaping. To display a literal %, use two consecutive % (%%), which the engine temporarily replaces with an internal placeholder [(*&*%^*$^%#%%^^&&*^*&(^))] before restoring to % after all variables are processed.
• %{} expressions support nested parentheses, using a bracket-counting algorithm to find matching closing brackets.
• Unmatched %variable or mismatched %{} brackets are preserved as-is.
• %variable substitution happens before %{} evaluation, so system variables inside %{} are already replaced with their numeric values.
• Temperature variables may return -1 (unavailable) on some devices; use conditional checks in UI to handle this.

Related

• UniDeskTempleteMgr — Template system, passes custom variables via presets
• UniDeskSystemInfo — System data source
• UDCText — Text control using expressions