I am using VS Code.
Supposedly there is a function called inspect() in dart that allows you to vardump an object.
my barebones example is as follows:
import 'dart:developer';
class User {
String name;
int age;
User(this.name, this.age);
}
void main() {
User newUser = User("Steve", 30);
inspect(newUser);
print('done');
}
I don't get any errors, but all I see in the Debug Console is "done"
On this page there is am image showing inspect() sample output (4th image from the top) in the Debug Console:
Link
Is there something else I need to do to make this command work in VS Code?
Recently I was trying out some code snippets from "Dart For Absolute Beginners" on DartPad.
Specifically:
import 'dart:math';
import 'dart:io';
void main()
{
int guess;
Random rand = new Random(); //create a random number generator
int answer = rand.nextInt(100); //gets a random integer from 0 to 99
do
{
print("Enter your guess:");
String temp = stdin.readLineSync(); //read in from the keyboard
guess = int.parse(temp); //convert String to integer
if (guess < answer)
{
print("Too low!");
}
else if (guess > answer)
{
print("Too high!");
}
}
while (guess != answer);
print("You got it!");
}
However upon running, it shows the error "Error compiling to JavaScript:
unsupported import: dart:io"
So my question is
Is it that we can't run I/O operations on DartPad and we need a full fledge editor for that ?
or is there something else wrong ??
The dart:io library is not supported in DartPad. However you can use this Dart compiler, it supports dart:io.
As noted in the dart:io documentation:
Important: Browser-based apps can't use this library. Only the following can import and use the dart:io library:
Servers
Command-line scripts
Flutter mobile apps
Flutter desktop apps
I try to use the same code for both web and android. Where the code differs I switch between widgets based on a global variable.
Is the performance worse when using a non constant / non final variable when switching between widgets? I'm thinking, because the variable is not final or constant and can be changed at any point, Flutter will not be able to optimise the code. Is that true? If inefficient, how do I make my code efficient?
eg.
I have two main files and set my AppType enum in each
[appType.dart]
AppType appType; //can't think of how to make this constant or final
[android_main.dart]
void main() {
appType = AppType.and;
[web_main.dart]
void main() {
appType = AppType.and;
In my widgets I switch where I need a widget specific for the web or android
if(appType == AppType.web)
return MyWidgetWeb();
else
return MyWeigetAnd();
Yes, a constant is more efficient, mainly because of tree-shaking.
Assume that you have the following types:
enum AppType {
mobile,
web,
}
class Mobile {}
class Web {}
Then when you write:
const type = AppType.web;
void main() {
if (type == AppType.web) {
print(Web());
}
else if (type == AppType.mobile) {
print(Mobile());
}
}
Then when compiling the code, the compiler knows that the if block will always be reached, and the else if never will.
As such:
the conditions are removed. When compiled, the code will be:
const type = AppType.web;
void main() {
// no `if` performed
print(Web());
}
Mobile will not be bundled in the executable, so you have a lighter application.
To fully benefit from this behavior, you can use Dart "defines", using int/bool/String.fromEnvironment, which allows you to define constants that behave differently depending on some external build parameters.
The way such constant would look like is:
const isWeb = bool.fromEnvironment('isWeb', defaultValue: false);
Which you can then control using arguments on flutter run and flutter build commands:
flutter build <whatever> --dart-define=isWeb=true
I am working on a Vala GTK application that starts minimized by default and I want to bind a specific keyword shortcut to bring the minimized window to the front.
I am able to handle Keyboard events using Accelerators when the app is focus ed, but I am unable to intercept any key press from the system when the app is minimized.
How can I make the app listen to system keyboard events so I can detect the key press accordingly?
Thank you.
I took a look at the source for Ideogram to see how it registers Super-e as a hot-key. It looks to be basically the following, including first checking that a custom hot-key has not already been registered for the application.
// These constants are set at class level.
public const string SHORTCUT = "<Super>e";
public const string ID = "com.github.cassidyjames.ideogram";
// Set shortcut within activate method.
CustomShortcutSettings.init ();
bool has_shortcut = false;
foreach (var shortcut in CustomShortcutSettings.list_custom_shortcuts ()) {
if (shortcut.command == ID) {
has_shortcut = true;
return;
}
}
if (!has_shortcut) {
var shortcut = CustomShortcutSettings.create_shortcut ();
if (shortcut != null) {
CustomShortcutSettings.edit_shortcut (shortcut, SHORTCUT);
CustomShortcutSettings.edit_command (shortcut, ID);
}
}
It uses a CustomShortcutSettings class included in its source to handle the reading and writing to the system settings. The class originated in another application called Clipped.
I'm looking for a way to execute code in Flutter when the app is in Debug mode. Is that possible in Flutter? I can't seem to find it anywhere in the documentation.
Something like this
If(app.inDebugMode) {
print("Print only in debug mode");
}
How can I check if the Flutter application is running in debug or release mode?
In later versions, you can use kDebugMode:
if (kDebugMode)
doSomething();
While asserts can technically be used to manually create an "is debug mode" variable, you should avoid that.
Instead, use the constant kReleaseMode from package:flutter/foundation.dart
The difference is all about tree shaking.
Tree shaking (aka the compiler removing unused code) depends on variables being constants.
The issue is, with asserts our isInReleaseMode boolean is not a constant. So when shipping our app, both the dev and release code are included.
On the other hand, kReleaseMode is a constant. Therefore the compiler is correctly able to remove unused code, and we can safely do:
if (kReleaseMode) {
} else {
// Will be tree-shaked on release builds.
}
Here is a simple solution to this:
import 'package:flutter/foundation.dart';
Then you can use kReleaseMode like
if(kReleaseMode){ // Is Release Mode??
print('release mode');
} else {
print('debug mode');
}
Please use Remi's answer with kReleaseMode and kDebugMode or Dart compilation won't be able to tree-shake your code.
This little snippet should do what you need:
bool get isInDebugMode {
bool inDebugMode = false;
assert(inDebugMode = true);
return inDebugMode;
}
If not, you can configure your IDE to launch a different main.dart in debug mode where you can set a Boolean.
kDebugMode
You can now use the kDebugMode constant.
if (kDebugMode) {
// Code here will only be included in debug mode.
// As kDebugMode is a constant, the tree shaker
// will remove the code entirely from compiled code.
} else {
}
This is preferable over !kReleaseMode as it also checks for profile mode, i.e., kDebugMode means not in release mode and not in profile mode.
kReleaseMode
If you just want to check for release mode and not for profile mode, you can use kReleaseMode instead:
if (kReleaseMode) {
// Code here will only be run in release mode.
// As kReleaseMode is a constant, the tree shaker
// will remove the code entirely from other builds.
} else {
}
kProfileMode
If you just want to check for profile mode and not for release mode, you can use kProfileMode instead:
if (kProfileMode) {
// Code here will only be run in release mode.
// As kProfileMode is a constant, the tree shaker
// will remove the code entirely from other builds.
} else {
}
While this works, using constants kReleaseMode or kDebugMode is preferable. See Rémi's answer below for a full explanation, which should probably be the accepted question.
The easiest way is to use assert as it only runs in debug mode.
Here's an example from Flutter's Navigator source code:
assert(() {
if (navigator == null && !nullOk) {
throw new FlutterError(
'Navigator operation requested with a context that does not include a Navigator.\n'
'The context used to push or pop routes from the Navigator must be that of a '
'widget that is a descendant of a Navigator widget.'
);
}
return true;
}());
Note in particular the () at the end of the call - assert can only operate on a Boolean, so just passing in a function doesn't work.
Not to be picky, but the foundation package includes a kDebugMode constant.
So:
import 'package:flutter/foundation.dart' as Foundation;
if(Foundation.kDebugMode) {
print("App in debug mode");
}
I believe the latest way to do this is:
const bool prod = const bool.fromEnvironment('dart.vm.product');
src
Just import this
import 'package:flutter/foundation.dart'
String bulid = kReleaseMode ? "Release" : "";
or
String bulid = kDebugMode ? "Debug" : "";
or
String bulid = kProfileMode ? "Profile" : "";
Or try this
if (kDebugMode) {
print("Debug");
} else if (kReleaseMode) {
print("Release");
} else if (kProfileMode) {
print("Profile");
}
Make a file named constants.dart. Add these variables in it:
const bool kReleaseMode = bool.fromEnvironment('dart.vm.product');
const bool kProfileMode = bool.fromEnvironment('dart.vm.profile');
const bool kDebugMode = !kReleaseMode && !kProfileMode;
printk(String string) {
if (kDebugMode) {
// ignore: avoid_print
print(string);
}
}
Then import this constant file in any other file and use it like this:
import 'package:package_name/constants.dart';
if(kDebugMode){
//Debug code
}else{
//Non-Debug code
}
printk("Debug Log");
I've created this useful class, based on other answers and inspired on Android usage.
If anything changes on "Foundation" package, it would not be necessary to change the entire application, it would be necessary to change only this class.
import 'package:flutter/foundation.dart' as Foundation;
abstract class Build {
static const bool isDebugMode = Foundation.kDebugMode;
static const bool isReleaseMode = Foundation.kReleaseMode;
static const bool isWeb = Foundation.kIsWeb;
static const bool isProfileMode = Foundation.kProfileMode;
}
Extracted from Dart Documentation:
When exactly do assertions work? That depends on the tools and
framework you’re using:
Flutter enables assertions in debug mode.
Development-only tools such as dartdevc typically enable assertions by default.
Some tools, such as dart and dart2js, support assertions through a command-line flag: --enable-asserts.
In production code, assertions are ignored, and the arguments to
assert aren’t evaluated.