Flutter錯誤：無法在“WidgetsBinding”上呼叫方法“addPostFrameCallback”？因為它可能為空-有解無憂

每當我嘗試運行顫振應用程式時，我都會收到此錯誤。

../flutter/.pub-cache/hosted/pub.dartlang.org/percent_indicator-4.2.1/lib/linear_percent_indicator.dart:162:5: Warning: The class 'WidgetsBinding' cannot be null.
Try replacing '?.' with '.'
    WidgetsBinding?.instance.addPostFrameCallback((_) {
    ^^^^^^^^^^^^^^
../flutter/.pub-cache/hosted/pub.dartlang.org/percent_indicator-4.2.1/lib/linear_percent_indicator.dart:162:30: Error: Method 'addPostFrameCallback' cannot be called on 'WidgetsBinding?' because it is potentially null.
 - 'WidgetsBinding' is from 'package:flutter/src/widgets/binding.dart' ('../flutter/packages/flutter/lib/src/widgets/binding.dart').
Try calling using ?. instead.
    WidgetsBinding?.instance.addPostFrameCallback((_) {
                             ^^^^^^^^^^^^^^^^^^^^


FAILURE: Build failed with an exception.

* Where:
Script '/home/user/Downloads/flutter/packages/flutter_tools/gradle/flutter.gradle' line: 1102

* What went wrong:
Execution failed for task ':app:compileFlutterBuildDebug'.
> Process 'command '/home/user/Downloads/flutter/bin/flutter'' finished with non-zero exit value 1

* Try:
Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output. Run with --scan to get full insights.

* Get more help at https://help.gradle.org

BUILD FAILED in 22s
Running Gradle task 'assembleDebug'...                             22.8s
Exception: Gradle task assembleDebug failed with exit code 1

這是我的 Flutter 醫生輸出

[?] Flutter (Channel stable, 2.10.3, on Ubuntu 20.04.4 LTS 5.13.0-41-generic, locale en_IN)
    ? Flutter version 2.10.3 at /home/user/Downloads/flutter
    ? Upstream repository https://github.com/flutter/flutter.git
    ? Framework revision 7e9793dee1 (3 months ago), 2022-03-02 11:23:12 -0600
    ? Engine revision bd539267b4
    ? Dart version 2.16.1
    ? DevTools version 2.9.2

[?] Android toolchain - develop for Android devices (Android SDK version 32.1.0-rc1)
    ? Android SDK at /home/user/Android/Sdk
    ? Platform android-32, build-tools 32.1.0-rc1
    ? Java binary at: /opt/android-studio-2021.1.1/android-studio/jre/bin/java
    ? Java version OpenJDK Runtime Environment (build 11.0.11 0-b60-7590822)
    ? All Android licenses accepted.

[?] Chrome - develop for the web
    ? Chrome at google-chrome

[?] Android Studio (version 2021.1)
    ? Android Studio at /opt/android-studio-2021.1.1/android-studio
    ? Flutter plugin version 66.0.1
    ? Dart plugin version 211.7811
    ? Java version OpenJDK Runtime Environment (build 11.0.11 0-b60-7590822)

[?] Android Studio
    ? Android Studio at /opt/android-studio
    ? Flutter plugin can be installed from:
      ?? https://plugins.jetbrains.com/plugin/9212-flutter
    ? Dart plugin can be installed from:
      ?? https://plugins.jetbrains.com/plugin/6351-dart
    ? Java version OpenJDK Runtime Environment (build 11.0.11 0-b60-7590822)

[?] Connected device (2 available)
    ? sdk gphone64 x86 64 (mobile) ? emulator-5554 ? android-x64    ? Android 12 (API 31) (emulator)
    ? Chrome (web)                 ? chrome        ? web-javascript ? Google Chrome 99.0.4844.82

[?] HTTP Host Availability
    ? All required HTTP hosts are available

? No issues found!

我已經嘗試過以下事情

使 android-studio 失效并重啟
洗掉 .gradle 檔案夾并再次嘗試構建
flutter clean然后“顫振 pub 獲得, 顫振 pub 快取修復”
- 還洗掉了構建檔案夾和 pubspec.lock 檔案

但沒有，作業

另外，這是我的 Gradle 檔案

android/app/build.gradle

def localProperties = new Properties()
def localPropertiesFile = rootProject.file('local.properties')
if (localPropertiesFile.exists()) {
    localPropertiesFile.withReader('UTF-8') { reader ->
        localProperties.load(reader)
    }
}

def flutterRoot = localProperties.getProperty('flutter.sdk')
if (flutterRoot == null) {
    throw new GradleException("Flutter SDK not found. Define location with flutter.sdk in the local.properties file.")
}

def flutterVersionCode = localProperties.getProperty('flutter.versionCode')
if (flutterVersionCode == null) {
    flutterVersionCode = '1'
}

def flutterVersionName = localProperties.getProperty('flutter.versionName')
if (flutterVersionName == null) {
    flutterVersionName = '1.0'
}

apply plugin: 'com.android.application'
apply plugin: 'kotlin-android'
apply from: "$flutterRoot/packages/flutter_tools/gradle/flutter.gradle"
apply plugin: 'com.google.gms.google-services'
android {
    compileSdkVersion flutter.compileSdkVersion

    compileOptions {
        sourceCompatibility JavaVersion.VERSION_1_8
        targetCompatibility JavaVersion.VERSION_1_8
    }

    kotlinOptions {
        jvmTarget = '1.8'
    }

    sourceSets {
        main.java.srcDirs  = 'src/main/kotlin'
    }
    splits {
        abi {
            enable true
            reset()
            include 'x86', 'armeabi-v7a'
            universalApk true
        }
    }
    defaultConfig {
        // TODO: Specify your own unique Application ID (https://developer.android.com/studio/build/application-id.html).
        applicationId "com.example.app.example"
        minSdkVersion 19
        targetSdkVersion flutter.targetSdkVersion
        versionCode flutterVersionCode.toInteger()
        versionName flutterVersionName
        multiDexEnabled = true
    }
    // signingConfigs {
    //     debug {
    //         if (debugKeystorePropertiesFile.exists()) {
    //             keyAlias debugKeystoreProperties['keyAlias']
    //             keyPassword debugKeystoreProperties['keyPassword']
    //             storeFile file(debugKeystoreProperties['storeFile'])
    //             storePassword debugKeystoreProperties['storePassword']
    //         }
    //     }
    // }
    buildTypes {
        release {
//            if (keystorePropertiesFile.exists()) {
//                signingConfig signingConfigs.release
//                println "Signing with key.properties"
//            } else {
                signingConfig signingConfigs.debug
                println "Signing with debug keys"
//            }
        }
    }
}

flutter {
    source '../..'
}

dependencies {
    implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk7:$kotlin_version"
    implementation platform('com.google.firebase:firebase-bom:29.2.1')
    implementation 'com.google.firebase:firebase-auth-ktx'
    implementation 'com.google.android.gms:play-services-safetynet:18.0.1'
    implementation 'com.google.firebase:firebase-appcheck-safetynet:16.0.0-beta05'

    implementation "androidx.browser:browser:1.3.0"
}

安卓/build.gradle

buildscript {
    ext.kotlin_version = '1.6.10'
    repositories {
        google()
        mavenCentral()
    }

    dependencies {
        classpath 'com.android.tools.build:gradle:4.1.0'
        classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
        classpath 'com.google.gms:google-services:4.3.10'
    }
}

allprojects {
    repositories {
        google()
        mavenCentral()
    }
}

rootProject.buildDir = '../build'
subprojects {
    project.buildDir = "${rootProject.buildDir}/${project.name}"
}
subprojects {
    project.evaluationDependsOn(':app')
}

task clean(type: Delete) {
    delete rootProject.buildDir
}

我確實添加了android.useAndroidX和android.enableJetifier為真
還添加android:exported="true"在 androidmanifest.xml 中

uj5u.com熱心網友回復：

將您的 percent_indicator 依賴項更改pubspec.yaml為：

percent_indicator: #update flutter 3
git:
  url: https://github.com/XuannThucc/flutter_percent_indicator.git
  ref: be51b3d56e729ca1889f77a5f6311b5287fa611d

uj5u.com熱心網友回復：

你應該改變

WidgetsBinding?.instance.addPostFrameCallback

到

WidgetsBinding.instance?.addPostFrameCallback

uj5u.com熱心網友回復：

似乎包將 null 感知運算子放在 WidgetsBinding 而不是實體上。

dart:162:5：警告：“WidgetsBinding”類不能為空。嘗試替換 '?.' 和 '。' WidgetsBinding?.instance.addPostFrameCallback((_) { ^^^^^^^^^^^^^^

它應該是：

WidgetsBinding.instance?.addPostFrameCallback((_) {

uj5u.com熱心網友回復：

你?的位置不對。嘗試像這樣更改代碼

// WidgetsBinding?.instance.addPostFrameCallback
-> WidgetsBinding.instance?.addPostFrameCallback

uj5u.com熱心網友回復：

通過將 percent_indicator 庫添加到本地專案來解決。

在那我改變了，這

WidgetsBinding?.instance.addPostFrameCallback((_) {
                             ^^^^^^^^^^^^^^^^^^^^

對此

WidgetsBinding?.instance?.addPostFrameCallback((_) {

它正在作業

謝謝大家的回復

uj5u.com熱心網友回復：

使用 percent_indicator 4.0.1 版。更高版本被定制為顫振3.0，所以你有一個錯誤。或者將flutter升級到3.0版本

Flutter 錯誤：無法在“WidgetsBinding”上呼叫方法“addPostFrameCallback”？因為它可能為空

轉載請註明出處，本文鏈接：https://www.uj5u.com/houduan/476112.html

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