Question

捕捉快照后，我一直试图在屏幕上打印base64编码的图像字符串。以下是代码。

import 'dart:io';
import 'package:image_picker/image_picker.dart';
import 'package:flutter/material.dart';
import 'dart:async';
import 'dart:convert';

import 'package:http/http.dart' as http;

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
    // This widget is the root of your application.
    @override
    Widget build(BuildContext context) {
        return MaterialApp(
        title: 'Flutter Demo',
        theme: ThemeData(

        primarySwatch: Colors.blue,
     ),
     home: MyHomePage(title: 'Flutter Demo Home Page'),
   );
  }
 }

class MyHomePage extends StatefulWidget {
    MyHomePage({Key key, this.title}) : super(key: key);



    final String title;

   @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {

    File _image;







     Future<String> getb64Image() async {
        List<int> imageBytes= await _image.readAsBytes();
        String b64image= base64Encode(imageBytes);
        print('In future func: $b64image\n');
         return b64image;
     }

     void clickPic() async {
       var image= await ImagePicker.pickImage(source: ImageSource.camera);
       setState(() {
         _image=image;
       });
   }

  Widget getImage(){
    return FutureBuilder<String>(
    future: getb64Image(),
    builder: (BuildContext context,AsyncSnapshot<String> snapshot){
    if(snapshot.connectionState==ConnectionState.done){
      if(snapshot.hasData){
        print('In snapshot : ${snapshot.data}');
        return new Text(snapshot.data);
      }
      else{
        return CircularProgressIndicator();
      }
    }
    else{
      return CircularProgressIndicator();
    }
  },
);
}


@override
Widget build(BuildContext context) {

 return Scaffold(
   appBar: AppBar(

    title: Text(widget.title),
  ),
  body: Center(

    child: Column(

      mainAxisAlignment: MainAxisAlignment.center,
      children: <Widget>[



        Center(
          child: _image!=null?getImage():Container(child: Text(
            'Click below to take a snap',
            style: Theme.of(context).textTheme.display1,
          ),),
        ),



        RaisedButton.icon(onPressed: clickPic,
            icon: Icon(Icons.camera),

            label:Text('click me to take a snap'),

        )

      ],
    ),
  ),

);
 }
 }

我的flutter版本为1.2.1，并且我正在使用Android Studio 3.3。问题是应用程序运行正常直到拍下快照，而当试图将b64转换后的图像字符串显示在屏幕上时，futurebuilder却不构建任何东西。该应用程序甚至没有CircularProgressIndicator的动画而卡住，并突然停止。除了“应用程序完成”或“与设备的连接断开”之外，控制台不会显示任何错误。我放入FutureBuilder和b64Image方法中的调试行可以工作，但是唯一的问题是FutureBuilder在不打印字符串的情况下崩溃了。请注意，我正在android模拟器上运行该应用程序。

这是在模拟器中运行代码的示例的链接：https://youtu.be/291sQtow3Q4

以下是控制台日志：

Launching lib/main.dart on Android SDK built for x86 in debug mode...
Initializing gradle...
Resolving dependencies...
Running Gradle task 'assembleDebug'...
Built build/app/outputs/apk/debug/app-debug.apk.
Installing build/app/outputs/apk/app.apk...
I/.flutter_pylen(12574): Background young concurrent copying GC freed      3846(621KB) AllocSpace objects, 3(60KB) LOS objects, 84% free, 1103KB/7247KB, paused 214us total 119.231ms
Syncing files to device Android SDK built for x86...
I/Choreographer(12574): Skipped 92 frames!  The application may be doing too much work on its main thread.
D/EGL_emulation(12574): eglMakeCurrent: 0xdb612b40: ver 2 0 (tinfo 0xdb608da0)
I/OpenGLRenderer(12574): Davey! duration=1686ms; Flags=1,    IntendedVsync=3188489793352, Vsync=3190023126624,   OldestInputEvent=9223372036854775807, NewestInputEvent=0, HandleInputStart=3190028534473, AnimationStart=3190028585003, PerformTraversalsStart=3190028607203, DrawStart=3190037234683, SyncQueued=3190038151683, SyncStart=3190052614713, IssueDrawCommandsStart=3190052729313, SwapBuffers=3190081882083,  FrameCompleted=3190190896713, DequeueBufferDuration=59694000,  QueueBufferDuration=238000, 
 D/        (12574): HostConnection::get() New Host Connection established 0xd68cab80, tid 12598
 D/        (12574): HostComposition ext ANDROID_EMU_CHECKSUM_HELPER_v1 ANDROID_EMU_dma_v1 GL_OES_vertex_array_object  GL_KHR_texture_compression_astc_ldr ANDROID_EMU_gles_max_version_2 
 D/EGL_emulation(12574): eglMakeCurrent: 0xec6e9660: ver 2 0 (tinfo 0xd67b6d40)
 D/EGL_emulation(12574): eglMakeCurrent: 0xdb612b40: ver 2 0 (tinfo 0xdb608da0)
 D/EGL_emulation(12574): eglCreateContext: 0xec6e9840: maj 2 min 0 rcv 2
 D/EGL_emulation(12574): eglMakeCurrent: 0xec6e9840: ver 2 0 (tinfo 0xd67b6c20)
 D/EGL_emulation(12574): eglMakeCurrent: 0xdb612b40: ver 2 0 (tinfo 0xdb608da0)
 D/EGL_emulation(12574): eglMakeCurrent: 0xec6e9840: ver 2 0 (tinfo 0xd67b6d40)
 I/flutter (12574): In future func: /9j/4AAQSkZJRgABAQAAAQABAAD 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
I/flutter (12574): In snapshot : 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
 Application finished.

我遇到的问题是没有显示错误。因此，我无法理解问题所在。有人可以在这里帮助我吗？

Answer 1

由于Dart VM花费太多时间来渲染“胖”文本数据，您的android进程似乎被杀死了。

您应该看到类似以下的日志：

03-17 20:03:55.922   712   712 I Zygote  : Process 12250 exited due to signal (9)

和

I/Choreographer(20099): Skipped 72 frames!  The application may be doing too much work on its main thread.

在Android logcat中为您的进程搜索exited due to signal。

基本上是Text widget could not handle string with millions of characters 可能是试图一次在主线程上渲染太多文本。

在这种情况下，虽然可能会出现一些不稳定的开发人员消息，但目前还没有任何消息。提出了同样的问题：https://github.com/flutter/flutter/issues/29510

FutureBuilder不返回小部件

1 个答案: