šØļø Project: Table Printer
š Lesson 8: Polish Your CLI
ā± 25-30 min
š Intermediate
šÆ Objective
Build a formatted table printer that displays data in clean, aligned columns with borders, headers, and customizable alignment. Perfect for CLI data display.
Requirements
- Create a
TablePrinterclass that formats data into tables - Support column headers with customizable alignment (left, center, right)
- Use
StringBufferfor efficient table building - Support different border styles (single, double, rounded, none)
- Auto-size columns based on content width
// Step 1: Alignment enum
enum TextAlignment { left, center, right }
// Step 2: Border style enum
enum BorderStyle { single, double, rounded, simple, none }
// Step 3: Column definition
class Column {
final String header;
final TextAlignment alignment;
final int? fixedWidth;
Column(this.header, {this.alignment = TextAlignment.left, this.fixedWidth});
}
// Step 4: Table printer class
class TablePrinter {
final List columns;
final BorderStyle borderStyle;
String _title = '';
TablePrinter(this.columns, {this.borderStyle = BorderStyle.single});
void setTitle(String title) {
_title = title;
}
String render(List> rows) {
final buffer = StringBuffer();
// Calculate column widths
List widths = _calculateWidths(rows);
// Border characters
final border = _getBorderChars();
// Title
if (_title.isNotEmpty) {
int totalWidth = widths.reduce((a, b) => a + b) + (columns.length * 3) + 1;
buffer.writeln(_centerText(_title, totalWidth));
}
// Top border
buffer.writeln(_buildBorder(widths, border.topLeft, border.top, border.topRight, border.horizontal));
// Header row
buffer.writeln(_buildRow(columns.map((c) => c.header).toList(), widths, border.vertical));
// Header separator
buffer.writeln(_buildBorder(widths, border.midLeft, border.mid, border.midRight, border.horizontal));
// Data rows
for (var row in rows) {
List values = row.map((v) => v.toString()).toList();
buffer.writeln(_buildRow(values, widths, border.vertical));
}
// Bottom border
buffer.writeln(_buildBorder(widths, border.bottomLeft, border.bottom, border.bottomRight, border.horizontal));
// Row count
buffer.write('${rows.length} row(s)');
return buffer.toString();
}
List _calculateWidths(List> rows) {
List widths = [];
for (int i = 0; i < columns.length; i++) {
int maxWidth = columns[i].header.length;
for (var row in rows) {
if (i < row.length) {
int cellWidth = row[i].toString().length;
if (cellWidth > maxWidth) maxWidth = cellWidth;
}
}
// Apply fixed width if specified
if (columns[i].fixedWidth != null) {
maxWidth = columns[i].fixedWidth!;
}
widths.add(maxWidth + 2); // Add padding
}
return widths;
}
String _buildRow(List values, List widths, String separator) {
final buffer = StringBuffer();
buffer.write(separator);
for (int i = 0; i < columns.length; i++) {
String value = i < values.length ? values[i] : '';
String padded = _alignText(value, widths[i], columns[i].alignment);
buffer.write(padded);
buffer.write(separator);
}
return buffer.toString();
}
String _alignText(String text, int width, TextAlignment alignment) {
if (text.length >= width) {
return ' ${text.substring(0, width - 2)} ';
}
int padding = width - text.length;
switch (alignment) {
case TextAlignment.left:
return ' $text${' ' * (padding - 1)}';
case TextAlignment.right:
return '${' ' * (padding - 1)}$text ';
case TextAlignment.center:
int leftPad = padding ~/ 2;
int rightPad = padding - leftPad;
return '${' ' * leftPad}$text${' ' * rightPad}';
}
}
String _centerText(String text, int width) {
if (text.length >= width) return text;
int padding = (width - text.length) ~/ 2;
return '${' ' * padding}$text';
}
String _buildBorder(List widths, String left, String mid, String right, String horizontal) {
final buffer = StringBuffer();
buffer.write(left);
for (int i = 0; i < widths.length; i++) {
buffer.write(horizontal * widths[i]);
if (i < widths.length - 1) {
buffer.write(mid);
}
}
buffer.write(right);
return buffer.toString();
}
_BorderChars _getBorderChars() {
switch (borderStyle) {
case BorderStyle.single:
return _BorderChars('ā', 'ā¬', 'ā', 'ā', 'ā¼', 'ā¤', 'ā', 'ā“', 'ā', 'ā', 'ā');
case BorderStyle.double:
return _BorderChars('ā', 'ā¦', 'ā', 'ā ', 'ā¬', 'ā£', 'ā', 'ā©', 'ā', 'ā', 'ā');
case BorderStyle.rounded:
return _BorderChars('ā', 'ā¬', 'ā®', 'ā', 'ā¼', 'ā¤', 'ā°', 'ā“', 'āÆ', 'ā', 'ā');
case BorderStyle.simple:
return _BorderChars('+', '+', '+', '+', '+', '+', '+', '+', '+', '|', '-');
case BorderStyle.none:
return _BorderChars('', ' ', '', '', ' ', '', '', ' ', '', ' ', ' ');
}
}
}
class _BorderChars {
final String topLeft, top, topRight;
final String midLeft, mid, midRight;
final String bottomLeft, bottom, bottomRight;
final String vertical, horizontal;
_BorderChars(
this.topLeft, this.top, this.topRight,
this.midLeft, this.mid, this.midRight,
this.bottomLeft, this.bottom, this.bottomRight,
this.vertical, this.horizontal,
);
}
// Step 5: Main program
void main() {
print('āāāāāāāāāāāāāāāāāāāāāāāāāāāāāāāāāāāā');
print('ā TABLE PRINTER ā');
print('āāāāāāāāāāāāāāāāāāāāāāāāāāāāāāāāāāāā\n');
// Define columns
final columns = [
Column('ID', alignment: TextAlignment.center, fixedWidth: 6),
Column('Name', alignment: TextAlignment.left),
Column('Age', alignment: TextAlignment.center),
Column('City', alignment: TextAlignment.left),
Column('Score', alignment: TextAlignment.right),
];
// Sample data
final data = [
[1, 'Alice Johnson', 28, 'New York', 95.5],
[2, 'Bob Smith', 35, 'Los Angeles', 87.3],
[3, 'Charlie Brown', 22, 'Chicago', 91.0],
[4, 'Diana Prince', 30, 'Houston', 98.7],
[5, 'Eve Wilson', 27, 'Phoenix', 76.4],
];
// Demo different styles
print('š Single Border Style:');
final table1 = TablePrinter(columns, borderStyle: BorderStyle.single);
table1.setTitle('STUDENT RECORDS');
print(table1.render(data));
print('\n\nš Double Border Style:');
final table2 = TablePrinter(columns, borderStyle: BorderStyle.double);
table2.setTitle('EMPLOYEE DATABASE');
print(table2.render(data));
print('\n\nš Rounded Border Style:');
final table3 = TablePrinter(columns, borderStyle: BorderStyle.rounded);
table3.setTitle('USER STATISTICS');
print(table3.render(data));
}