I have a memory image stored in Sqllite converted to String with the toString() method, I want to convert it to Unit8List to display it inside a MemoryImage widget
codeUnits gets you a List<int>
Uint8List.fromList(...) converts List<int> to Uint8List
String.fromCharCodes(...) converts List<int> or Uint8List to String
List<int> list = 'xxx'.codeUnits;
Uint8List bytes = Uint8List.fromList(list);
String string = String.fromCharCodes(bytes);
Use utf8.encode(myString) to convert String to bytes or List<int>,
And then convert it back using utf8.decode(bytes)
String source = 'Błonie';
List<int> list = utf8.encode(source);
Uint8List bytes = Uint8List.fromList(list);
String outcome = utf8.decode(bytes);
the best and simple way of doing it is,
Image.memory(base64decode(string_value_here))
Related
I wrote this code to convert dynamic list to Word list but linter says:
Omit type annotations for local variables. on 2nd line.
However if I omit type annotations, I get an error A value of type 'List<dynamic>' can't be returned from method 'convert' because it has a return type of 'List<Word>'.
It there any smarter way to convert?
static List<Word> convert(List<dynamic> words) {
final List<Word> wordsList = [];
words.forEach((v) {
final map = Map<String, dynamic>.from(v as Map<dynamic, dynamic>);
wordsList.add(Word.fromMap(map));
});
return wordsList;
}
Word.fromMap is:
Word.fromMap(Map<String, dynamic> map)
: text = map['text'] as String,
count = map['count'] as int;
To avoid the warning, and put the type on the right-hand side as the lint wants, just write:
final wordsList = <Word>[];
I assume words is JSON data, so the maps are already Map<String, dynamic>. Then you can also do everything in one line:
static List<Word> convert(List<dynamic> words) =>
[for (var v in words) Word.fromMap(v)];
Use the cast() method like this:
class Word {
final String text;
final int count;
static List<Word> convert(List<dynamic> words) {
final List<Word> wordsList = [];
words.cast<Map<dynamic, dynamic>>().forEach((v) { // <-- look here
final map = Map<String, dynamic>.from(v);
wordsList.add(Word.fromMap(map));
});
return wordsList;
}
Word.fromMap(Map<String, dynamic> map)
: text = map['text'] as String,
count = map['count'] as int;
}
It will ensure the casting are done on each element. Make sure the type are correct since it will else result in a type-cast error.
I'm getting a Bluetooth Characteristic from a Bluetooth controller with flutter blue as a List. This characteristic contains weight measurement of a Bluetooth scale. Is there a function to convert this list of ints to a Double?
I tried to find some background on float representations by reading the IEEE 754 standard. There is the dart library typed_data but I am new to dart and have no experience with this lib.
Example:
I have this List: [191, 100, 29, 173] which is coming from a bluetooth controller as a IEEE754 representation for a float value.
Now i believe i have to convert each int to hex and concat these values: bf 64 1d ad
Next thing need to do is convert this to double, but i cannot find a function to convert hex to double. Only int.parse("0xbf641dad").
I guess your mean to convert the list of ints to a list of floats, not to a single float, right?
First, dart has no type called float. Instead it has type double. To convert it, you can use the map() function:
var listInt = [1, 2, 3];
var listDouble = list.map((i) => i.toDouble()).toList();
Had this same issue.
I think you mean how do you make the four bytes into a float32 ?
I needed to do the same thing.
you will want to do something like this:
first take the List value as a byte buffer, then take the byte data, then you can use the getFloat32 function.
ByteBuffer buffer = new Int8List.fromList(value_in).buffer;
ByteData byteData = new ByteData.view(buffer);
result = byteData.getFloat32(0);
Just be a little aware that the order of bytes from the Bluetooth may be back to front, as the convention varys.
Also you will need the typed_data library:
import 'dart:typed_data'; //for data formatting
I'm trying to go in the other direction now . . . for the obvious reason.
You may need this:
double parseHexString(String hexStr, bool littleEndian){
if(hexStr.length % 2 != 0){
return 0;
}
if(littleEndian == true){
List<int> bytes = hex.decode(hexStr).reversed.toList();
hexStr = hex.encode(bytes);
}
var byteConvert = ByteData(12);
byteConvert.setInt64(0, int.parse(hexStr,radix: 16));
return byteConvert.getFloat64(0);}
And demo :
double lat = parseHexString("0000004069665E40",true);
//lat = 121.60017395019531
If you already have:
int.parse("0xbf641dad")
I don't see why this wouldn't work:
int.parse("0xbf641dad").toDouble();
I used dart:typed_data for this:
import 'dart:typed_data';
List<int> intList = [191, 100, 29, 173];
double asFloat = ByteData.view(Uint8List.fromList(List.from(intList)).buffer).getFloat32(0, Endian.little);
Library reference: https://api.dart.dev/be/136883/dart-typed_data/dart-typed_data-library.html
I am new to flutter and I just want to display a list of alphabets in a for loop. I just want to know how can I convert the integer to ascii character. I searched for this and I found dart:convert library, but I don't know how to use it.
I want something like -
for(int i=65; i<=90; i++){
print(ascii(i)); //ascii is not any method, its just to understand my question
}
It should print the letters from 'A' to 'Z'.
You don't need dart:convert, you can just use String.fromCharCode
print(String.fromCharCode(i));
More info: https://api.dartlang.org/stable/2.0.0/dart-core/String/String.fromCharCode.html
In Dart, use these 2 functions to convert from int (byte) to String (char) and vice versa.
int value = ';'.codeUnitAt(0); //get unicode for semicolon
String char = String.fromCharCode(value); //get the semicolon string ;
This ia exactly what you need to generate your alphabet:
import 'dart:core';
void RandomString() {
List<int> a = new List<int>.generate(26, (int index) => index + 65);
String f = String.fromCharCodes(a);
print(f);
}
void main() {
RandomString();
}
Also You can copy, paste and test it here https://dartpad.dartlang.org/
I've been searching for a way to convert decimal numbers to hexadecimal format in the Dart programming language.
The hex.encode method in the HexCodec class, for example, cannot convert the decimal 1111 (which has a hex value of 457) and instead gives an exception:
FormatException: Invalid byte 0x457. (at offset 0)
How do I convert a decimal number to hex?
int.toRadixString(16)
does that.
See also https://groups.google.com/a/dartlang.org/forum/m/#!topic/misc/ljkYEzveYWk
Here is a little fuller example:
final myInteger = 2020;
final hexString = myInteger.toRadixString(16); // 7e4
The radix just means the base, so 16 means base-16. You can use the same method to make a binary string:
final binaryString = myInteger.toRadixString(2); // 11111100100
If you want the hex string to always be four characters long then you can pad the left side with zeros:
final paddedString = hexString.padLeft(4, '0'); // 07e4
And if you prefer it in uppercase hex:
final uppercaseString = paddedString.toUpperCase(); // 07E4
Here are a couple other interesting things:
print(0x7e4); // 2020
int myInt = int.parse('07e4', radix: 16);
print(myInt); // 2020
I am extracting metadata of a song using following code ,And how I can convert the byte array (buf) to string? Please help me,Thanks in advance.
String mint = httpConnection.getHeaderField("icy-metaint");
int b = 0;
int count =0;
while(count++ < length){
b = inputStream.read();
}
int metalength = ((int)b)*16;
if(metalength <= 0)
return;
byte buf[] = new byte[metalength];
inputStream.read(buf,0,buf.length);
1). Read bytes from the stream:
// use net.rim.device.api.io.IOUtilities
byte[] data = IOUtilities.streamToBytes(inputStream);
2). Create a String from the bytes:
String s = new String(data, "UTF-8");
This implies you know the encoding the text data was encoded with before sending from the server. In the example right above the encoding is UTF-8. BlackBerry supports the following character encodings:
* "ISO-8859-1"
* "UTF-8"
* "UTF-16BE"
* "US-ASCII"
The default encoding is "ISO-8859-1". So when you use String(byte[] data) constructor it is the same as String(byte[] data, "ISO-8859-1").
If you don't know what encoding the server uses then I'd recommend to try UTF-8 first, because by now it has almost become a default one for servers. Also note the server may send the encoding via an http header, so you can extract it from the response. However I saw a lot of servers which put "UTF-8" into the header while actually use ISO-8859-1 or even ASCII for the data encoding.
String has a constructor that accepts a byte array that you can use for this.
See e.g. http://java.sun.com/javame/reference/apis/jsr139/java/lang/String.html
As #Heiko mentioned you can create string directly using the constructor. This applies to blackberry java too:
byte[] array = {1,2,3,4,5};
String str = new String(array);