FLUTTER - 有人可以帮我执行这个帖子按钮吗？

Question

我希望你们今天都做得很好。我有另一个颤振问题，过去几天我一直在坚持。我正在尝试将此数据上传到我的 firestore 实例，但我的发布按钮似乎从未触发。我试图从它调用的方法中打印一个语句，但我似乎也无法让它工作。我正在尝试创建一个社交媒体应用程序，我们将不胜感激。

我的主要目标是让 post 按钮在 upload.dart 中执行。

我还包括了 home.dart，因为这两个类在性能方面是相关的。

上传.dart

import 'dart:io';

import 'package:cached_network_image/cached_network_image.dart';
import 'package:firebase_storage/firebase_storage.dart';
import 'package:flutter/material.dart';
import 'package:flutter_svg/flutter_svg.dart';
import 'package:fluttermedia/models/user.dart';
import 'package:fluttermedia/pages/home.dart';
import 'package:fluttermedia/widgets/progress.dart';
import 'package:image_picker/image_picker.dart';
import 'package:path_provider/path_provider.dart';
import 'package:image/image.dart' as Im;
import 'package:uuid/uuid.dart';

class Upload extends StatefulWidget {
  final User currentUser;

  Upload({this.currentUser});

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

class _UploadState extends State<Upload> {
  TextEditingController locationController = TextEditingController();
  TextEditingController captionController = TextEditingController();
  File file;
  bool isUploading = false;
  String postId = Uuid().v4();

  handleChooseFromGallery() async{
    Navigator.pop(context);
    File file = await ImagePicker.pickImage(source: ImageSource.gallery);
    setState(() {
      this.file = file;
    });
  }

  handleTakePhoto() async {
    Navigator.pop(context);
    File file = await ImagePicker.pickImage(source: ImageSource.camera,maxHeight: 675,maxWidth: 960);
    setState(() {
      this.file = file;
    });
  }

  selectImage(parentContext){
    return showDialog(
        context: parentContext,
      builder: (context) {
          return SimpleDialog(
            title: Text("Create Post"),
            children: <Widget>[
              SimpleDialogOption(
                child: Text("Photo With Camera"),
                onPressed: handleTakePhoto,
              ),
              SimpleDialogOption(
                child: Text("Image from Gallery"),
                onPressed: handleChooseFromGallery,
              ),
              SimpleDialogOption(
                child: Text("Cancel"),
                onPressed: () => Navigator.pop(context),
              ),
            ],
          );
      }
    );
  }

  Container buildSplashScreen(){
    return Container(
      color: Theme.of(context).accentColor.withOpacity(0.6),
      child: Column(
        mainAxisAlignment: MainAxisAlignment.center,
        children: <Widget>[
          SvgPicture.asset('assets/images/upload.svg',height: 260.0,),
          Padding(
            padding: EdgeInsets.only(top:20.0),
            child: RaisedButton(
              shape: RoundedRectangleBorder(
                borderRadius: BorderRadius.circular(8.0),
              ),
              child: Text(
                "Upload Image",
                style: TextStyle(
                color: Colors.white,
                fontSize: 22.0,
                ),
              ),
              color: Colors.deepOrange,
              onPressed: () => selectImage(context),
            ),
          )
        ],
      ),

    );
  }

  clearImage(){
    setState(() {
      file = null;
    });
  }

  //This compresses images for firebase
  compressImage() async{
    final tempDir = await getTemporaryDirectory();
    final path = tempDir.path;
    Im.Image imageFile = Im.decodeImage(file.readAsBytesSync());
    final compressedImageFile = File('$path/img_$postId.jpg')..writeAsBytesSync(Im.encodeJpg(imageFile,quality: 85));
    setState(() {
      file = compressedImageFile;
    });
  }

  Future<String> uploadImage(imageFile) async{
    StorageUploadTask uploadTask = storageRef.child("post_$postId.jpg").putFile(imageFile);
    StorageTaskSnapshot storageSnap = await uploadTask.onComplete;
    String downloadUrl = await storageSnap.ref.getDownloadURL();
    return downloadUrl;
  }

  //upload new info to firestore that creates a new collection
  createPostInFirestore({String mediaUrl, String location, String description}){
    postsRef.document(widget.currentUser.id)
        .collection("userPosts")
        .document(postId)
        .setData({
      "postId": postId,
      "ownerId": widget.currentUser.id,
      "username": widget.currentUser.username,
      "mediaUrl": mediaUrl,
      "description": description,
      "location": location,
      "timestamp": timeStamp,
      "likes":{}
        });
  }

  //Getting the info from the caption, location and pic
  handleSubmit() async{
    setState(() {
      isUploading = true;
    });
    await compressImage();
    String mediaUrl = await uploadImage(file);
    createPostInFirestore(
      mediaUrl: mediaUrl,
      location: locationController.text,
      description: captionController.text,
    );
    captionController.clear();
    locationController.clear();
    setState(() {
      file = null;
      isUploading = false;
    });
  }

  Scaffold buildUploadForm(){
    return Scaffold(
      appBar: AppBar(
        backgroundColor: Colors.white70,
        leading: IconButton(
          icon: Icon(Icons.arrow_back,color: Colors.black,),
          onPressed: clearImage,
        ),
        title: Text(
          "Caption Post",
          style: TextStyle(color: Colors.black),
        ),
        actions: <Widget>[
          FlatButton(
            onPressed: () => isUploading ? null : () => handleSubmit(),
            child: Text(
                "Post",
              style: TextStyle(
                color: Colors.blueAccent,
                fontWeight: FontWeight.bold,
                fontSize: 20.0,
              ),
            ),
          )
        ],
      ),
      body: ListView(
        children: <Widget>[
          isUploading ? linearProgress(context):Text(""),
          Container(
            height: 220.0,
            width: MediaQuery.of(context).size.width*0.8,
            child: Center(
              child: AspectRatio(
                aspectRatio: 16/9,
                child: Container(
                  decoration: BoxDecoration(
                    image: DecorationImage(
                      fit: BoxFit.cover,
                      image: FileImage(file),
                    )
                  ),
                ),
              ),
            ),
          ),
          Padding(
            padding: EdgeInsets.only(top:10),
          ),
          ListTile(
            leading: CircleAvatar(
              backgroundImage: CachedNetworkImageProvider(widget.currentUser.photoUrl),
            ),
            title: Container(
              width: 250.0,
              child: TextField(
                controller: captionController,
                decoration: InputDecoration(
                  hintText: "Write a Caption...",
                  border: InputBorder.none,
                ),
              ),
            ),
          ),
          Divider(),
          ListTile(
            leading: Icon(Icons.pin_drop,color: Colors.orange,size: 35.0),
            title: Container(
              width: 250.0,
              child: TextField(
                controller: locationController,
                decoration: InputDecoration(
                  hintText: "Where was this photo taken",
                  border: InputBorder.none,
                ),
              ),
            ),
          ),
          Container(
            width: 200.0,
            height: 100.0,
            alignment: Alignment.center,
            child: RaisedButton.icon(
              label: Text(
                "Use Current Location",
                style: TextStyle(color: Colors.white),
              ),
              shape: RoundedRectangleBorder(
                  borderRadius: BorderRadius.circular(30.0),
              ),
              color: Colors.blue,
              onPressed: () => print("Get user location"),
              icon: Icon(
                Icons.my_location,
                color: Colors.white,
              ),
            ),
          )
        ],
      ),
    );
  }

  @override
  Widget build(BuildContext context) {
    return file == null ? buildSplashScreen() : buildUploadForm();
  }
}

home.dart

import 'package:cloud_firestore/cloud_firestore.dart';
import 'package:firebase_storage/firebase_storage.dart';
import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';
import 'package:fluttermedia/models/user.dart';
import 'package:fluttermedia/pages/activity_feed.dart';
import 'package:fluttermedia/pages/create_account.dart';
import 'package:fluttermedia/pages/profile.dart';
import 'package:fluttermedia/pages/search.dart';
import 'package:fluttermedia/pages/upload.dart';
import 'package:google_sign_in/google_sign_in.dart';

final GoogleSignIn googleSignIn = GoogleSignIn();
final StorageReference storageRef = FirebaseStorage.instance.ref();
final usersRef = Firestore.instance.collection('users');
final postsRef = Firestore.instance.collection('posts');
final DateTime timeStamp = DateTime.now();
User currentUser;

class Home extends StatefulWidget {
  @override
  _HomeState createState() => _HomeState();
}

class _HomeState extends State<Home> {

  bool isAuth = false;
  PageController pageController;
  int pageIndex = 0;

  @override
  void initState() {
    super.initState();
    pageController = PageController();
    // Detects if user signs in
    googleSignIn.onCurrentUserChanged.listen((account) {
      handleSignIn(account);
    }, onError: (err){
      print('Error sigining in: $err');
    });
    //Reauthenticate user when app is opened
    googleSignIn.signInSilently(suppressErrors: false)
    .then((account) =>
        handleSignIn(account)).catchError((err){
          print('Error signing in on retry: $err');
    });

  }

  @override
  Widget build(BuildContext context) {
    return isAuth ? buildAuthScreen() : buildUnAuthScreen();
  }

  @override
  void dispose(){
    pageController.dispose();
    super.dispose();
  }

  //Helper Functions
  //The sign in section of the code
  handleSignIn(GoogleSignInAccount account){
      if(account != null){
        createUserInFirestore();
        setState(() {
          isAuth = true;
        });
      }else{
        setState(() {
          isAuth = false;
        });
      }
  }

  login(){
    googleSignIn.signIn();
  }

  logout(){
    googleSignIn.signOut();
  }

  onPageChanged(int pageIndex){
    setState(() {
      this.pageIndex =  pageIndex;
    });
  }

  createUserInFirestore() async{
    // 1) Check if user exists in users collection in database (According to id)
    final GoogleSignInAccount user = googleSignIn.currentUser;
    DocumentSnapshot doc = await usersRef.document(user.id).get();
    if(!doc.exists){
      // 2) If the user doesn't exist, take them to create account page
      final username = await Navigator.push(context, MaterialPageRoute(builder: (context) => CreateAccount()));
      // 3) get username from create account, use it to make new user document in users collection
      usersRef.document(user.id).setData({
        "id":user.id,
        "username":username,
        "photoUrl": user.photoUrl,
        "email":user.email,
        "displayName": user.displayName,
        "bio":"",
        "timeStamp": timeStamp,
      });
      doc = await usersRef.document(user.id).get();
    }
    currentUser = User.fromDocument(doc);
    //print(currentUser);
    //print(currentUser.username);
  }

  onTap(int pageIndex){
    //This what you would use to animate in between the different screens
    pageController.animateToPage(
        pageIndex,
        duration: Duration(milliseconds: 300),
        curve: Curves.easeInOut
    );
  }

//UI Code
  Widget buildAuthScreen() {
    return Scaffold(
      body: PageView(
        children: <Widget>[
          //Timeline(),
          RaisedButton(
            child: Text('Logout'),
            onPressed: logout,
          ),
          ActivityFeed(),
          Upload(currentUser: currentUser),
          Search(),
          Profile(),
        ],
        controller: pageController,
        onPageChanged: onPageChanged,
        physics: NeverScrollableScrollPhysics(),
      ),
      bottomNavigationBar: CupertinoTabBar(
        currentIndex: pageIndex,
        onTap: onTap,
        activeColor: Theme.of(context).primaryColor,
        items: [
          BottomNavigationBarItem(icon: Icon(Icons.whatshot),),
          BottomNavigationBarItem(icon: Icon(Icons.notifications_active),),
          BottomNavigationBarItem(icon: Icon(Icons.photo_camera, size: 34.0,),),
          BottomNavigationBarItem(icon: Icon(Icons.search),),
          BottomNavigationBarItem(icon: Icon(Icons.account_circle),),
        ],
      ),
    );

    /*return RaisedButton(
      child: Text('Logout'),
      onPressed: logout,
    );*/
  }

  Scaffold buildUnAuthScreen() {
    return Scaffold(
      body: Container(
        width: MediaQuery.of(context).size.width,
        height: MediaQuery.of(context).size.height,
        decoration: BoxDecoration(
          gradient: LinearGradient(
            begin: Alignment.topRight,
            end: Alignment.bottomLeft,
            colors: [
              Theme.of(context).primaryColor,
              Theme.of(context).accentColor,
            ]
          )
        ),
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          crossAxisAlignment: CrossAxisAlignment.center,
          children: <Widget>[
            Text('FlutterMedia',
            style: TextStyle(
              fontFamily: "Signatra",
              fontSize: 90.0,
              color: Colors.white
            ),
            ),
            GestureDetector(
              onTap:() => login(),
              child: Container(
                width: 260,
                height: 60,
                decoration: BoxDecoration(
                  image: DecorationImage(
                    image: AssetImage('assets/images/google_signin_button.png'),
                    fit: BoxFit.cover,
                  ),
                ),
              ),
            )
          ],
        ),
      ),
    );
  }


}

Answer 1

onPressed: () => isUploading ? null : () => handleSubmit(),

嗯，这就是你的问题。当isUploading 为假时，您的意思是有一个第三条件使onPressed 调用handleSubmit。相反，您将onPressed 变成了一个返回函数的函数。

为了更清楚地说明这一点，让我们将这个函数分解为适当的非 lambda 函数和 if/else 块：

onPressed: () {
  if (isUploading) {
    return null;
  } else {
    return () {
      handleUpload();
    }
  }
}

因此，请考虑按下按钮时会发生什么。它调用外部函数，检查isUploading。如果为 true，则该函数返回 null，如果为 false，则返回另一个函数，如果调用该函数，则调用 handleUpload。所以这是怎么回事，onPressed 永远不会为 null（它有时只是返回 null）并且handleUpload 永远不会被调用（因为返回的内部函数永远不会被调用自身）。

去掉外层的 lambda，它就可以工作了：

onPressed: isUploading ? null : () => handleSubmit(),