Flutter打印缓冲区内容插件print_buffer的使用

在Flutter中，有时我们希望将print函数输出的内容缓存起来，而不是立即输出到控制台。print_buffer插件可以帮助我们实现这一需求。

使用

简单的print缓冲

print('Start buffering');

final buffer = PrintBuffer();
await buffer.overridePrint(() {
  print('Buffered');
});

print('End buffering');
stdout.write(buffer.buffer);

输出结果：

Start buffering
End buffering
Buffered

简单的stdout缓冲

stdout.writeln('Start buffering');

final buffer = PrintBuffer();
await buffer.overrideStdout(() {
  stdout.writeln('Buffered');
});

stdout.writeln('End buffering');
stdout.write(buffer.buffer);

输出结果：

Start buffering
End buffering
Buffered

暂停缓冲

print('Start buffering');

final buffer = PrintBuffer();
await buffer.overridePrint(() {
  print('Buffered 1');
  buffer.isBuffering = false;
  print('Buffering paused');
  buffer.isBuffering = true;
  print('Buffered 2');
});

print('End buffering');
stdout.write(buffer.buffer);

输出结果：

Start buffering
Buffering paused
End buffering
Buffered 1
Buffered 2

添加时间戳

使用转换器函数。每个函数接受一个字符串并返回一个字符串：

print('Start buffering');

final buffer = PrintBuffer(
  transformers: [utcDate, utcTimeSeconds],
);

await buffer.overridePrint(() {
  print('Buffered with timestamp');
  buffer.isBuffering = false;
  print('Buffering paused');
  buffer.isTransforming = false;
  print('Buffering and transforming paused');
  buffer.isBuffering = true;
  print('Buffered without timestamp');
});

print('End buffering');
stdout.write(buffer.buffer);  

输出结果：

Start buffering
2024-06-03 05:04:02Z Buffering paused
Buffering and transforming paused
End buffering
2024-06-03 05:04:02Z Buffered with timestamp
Buffered without timestamp

完整示例

以下是一个完整的示例代码，展示了如何使用print_buffer插件的不同功能。

import 'dart:io';

import 'package:print_buffer/print_buffer.dart';

Future<void> main() async {
  await runPrint();
  print('--');
  await runPrintTransformed();
  print('--');
  await runReturns();
  print('--');
  await runStdoutTransformed();
}

Future<void> runPrint() async {
  print('Start buffering print');

  final buffer = PrintBuffer();
  await buffer.overridePrint(() {
    print('Buffered unchanged 1');
    buffer.isBuffering = false;
    print('Buffering paused');
    buffer.isBuffering = true;
    print('Buffered unchanged 2');
  });

  print('End buffering print');
  stdout.write(buffer.buffer);
}

Future<void> runPrintTransformed() async {
  print('Start buffering print with timestamp');

  final buffer = PrintBuffer(
    transformers: [utcDate, utcTimeSeconds],
  );

  await buffer.overridePrint(() {
    stdout.writeln('Not buffering or transforming stdout');
    print('Buffered with timestamp');
    buffer.isBuffering = false;
    print('Buffering paused');
    buffer.isTransforming = false;
    print('Buffering and transforming paused');
    buffer.isBuffering = true;
    print('Buffered without timestamp');
  });

  print('End buffering print with timestamp');
  stdout.write(buffer.buffer);
}

Future<void> runReturns() async {
  final buffer = PrintBuffer();

  print('Start buffering print sync');
  print(
    await buffer.overridePrint(() {
      print('Buffered sync');
      return 'Sync result';
    }),
  );
  print('End buffering print sync');

  print('Start buffering print async');
  print(
    await buffer.overridePrint(() async {
      await Future.delayed(Duration.zero);
      print('Buffered async');
      return 'Async result';
    }),
  );
  print('End buffering print async');

  stdout.write(buffer.buffer);
}

Future<void> runStdoutTransformed() async {
  stdout.writeln('Start buffering stdout with timestamp');

  final buffer = PrintBuffer(
    transformers: [utcDate, utcTimeSeconds],
  );

  await buffer.overrideStdout(() {
    print('Not buffering or transforming print');
    stdout.write('Buffered with timestamp\n');
    buffer.isBuffering = false;
    stdout.write('Buffering paused\n');
    buffer.isTransforming = false;
    stdout.writeln('Buffering and transforming paused');
    buffer.isBuffering = true;
    stdout.writeln('Buffered without timestamp');
  });

  stdout.writeln('End buffering stdout with timestamp');
  stdout.write(buffer.buffer);
}