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json - 如何解决这个 "The getter ' 长度' was called on null"

我在我的大学服务器上托管了一个php文件,当我在服务器上运行该文件时,它运行良好。运行链接中的php文件后,我可以获得json数据http://www.alkadhum-col.edu.iq/Teachers%20Activities/get.php但是当我在应用程序屏幕上的抖动中尝试时无法得到它们时得到“getter'length'wascalledonnull”。import'package:flutter/material.dart';import'package:http/http.dart'ashttp;import'dart:convert';voidmain(){runA

python selenium报错ValueError: Timeout value connect was <...>, but it must be an int, float or None.

pythonselenium报错ValueError:Timeoutvalueconnectwas<…>,butitmustbeanint,floatorNone.因更换系统,重新安装了selenium。命令:pipinstallselenium默认版本为selenium4,版本不太兼容,所以卸载:pipuninstallselenium更换为旧版本:pipinstallselenium==3.141.0安装完以后显示:Successfullyinstalledselenium-3.141.0urllib3-2.0.2(坑出现了)运行一下代码以后报错:fromseleniumimportweb

android - flutter - 重新加载时奖励视频广告错误 : "ad_not_loaded, show failed for rewarded video, no ad was loaded, null)"

我尝试重新加载奖励视频广告,当我调用RewardedVideoAd.instance.load(adUnitId:"xxx",targetingInfo:xyz);我发现以下错误:W/MessageQueue(13672):Handler(android.os.Handler){1a13e8a}sendingmessagetoaHandleronadeadthreadW/MessageQueue(13672):java.lang.IllegalStateException:Handler(android.os.Handler){1a13e8a}sendingmessagetoaHand

android - flutter - 重新加载时奖励视频广告错误 : "ad_not_loaded, show failed for rewarded video, no ad was loaded, null)"

我尝试重新加载奖励视频广告,当我调用RewardedVideoAd.instance.load(adUnitId:"xxx",targetingInfo:xyz);我发现以下错误:W/MessageQueue(13672):Handler(android.os.Handler){1a13e8a}sendingmessagetoaHandleronadeadthreadW/MessageQueue(13672):java.lang.IllegalStateException:Handler(android.os.Handler){1a13e8a}sendingmessagetoaHand

flutter_local_notifications : "PlatformException (PlatformException(INVALID_ICON, 找不到资源))

我正在尝试使用flutter_local_notifications插件向我的应用程序添加通知,但AndroidInitializationSettings需要可绘制资源并在未提供时抛出此错误:"PlatformException(PlatformException(INVALID_ICON,Theresourcecouldnotbefound.PleasemakesureithasbeenaddedasadrawableresourcetoyourAndroidheadproject.,null))"问题是不知道Androidhead项目在哪 最佳答案

flutter_local_notifications : "PlatformException (PlatformException(INVALID_ICON, 找不到资源))

我正在尝试使用flutter_local_notifications插件向我的应用程序添加通知,但AndroidInitializationSettings需要可绘制资源并在未提供时抛出此错误:"PlatformException(PlatformException(INVALID_ICON,Theresourcecouldnotbefound.PleasemakesureithasbeenaddedasadrawableresourcetoyourAndroidheadproject.,null))"问题是不知道Androidhead项目在哪 最佳答案

android - NoSuchMethodError : The method 'validate' was called on null 错误

我是Flutter的初学者,这就是问题所在——我正在尝试构建一个带有验证和“提交”按钮的表单,该按钮必须导航到一个新屏幕,但存在“NoSuchMethodError:方法‘validate’被调用为空”当我按下这个按钮时在调试器中。这是代码:class_SignInPageextendsState{finalscaffoldKey=GlobalKey();finalformKey=GlobalKey();String_email;String_password;void_submit(){finalform=formKey.currentState;if(form.validate()

android - NoSuchMethodError : The method 'validate' was called on null 错误

我是Flutter的初学者,这就是问题所在——我正在尝试构建一个带有验证和“提交”按钮的表单,该按钮必须导航到一个新屏幕,但存在“NoSuchMethodError:方法‘validate’被调用为空”当我按下这个按钮时在调试器中。这是代码:class_SignInPageextendsState{finalscaffoldKey=GlobalKey();finalformKey=GlobalKey();String_email;String_password;void_submit(){finalform=formKey.currentState;if(form.validate()

解决cURL error 60: SSL: no alternative certificate subject name matches target host name ‘test.com‘

 按照提示前往libcurl-ErrorCodes说是SSL证书问题 解决方法:1.前往该路径下载https://curl.se/ca/cacert.pem 将文件里的内容全部复制下来,然后替换上图路径的/ca-bundle.crt 里面的内容保存即可若行不通可以尝试第二种方法2.在执行curl操作前在前面加上如下代码$ch=curl_init();curl_setopt($ch,CURLOPT_URL,"https://test.com/");curl_setopt($ch,CURLOPT_HEADER,false);//原本的代码段//...//...//...curl_close($ch

notifications - Flutter:如何仅当我们使用 local_notification 单击通知时才执行操作?

我正在使用local_notification显示通知,我想在单击通知时执行一个操作(例如,在新窗口中打开新信号的消息)。我试着用onNotificationClick:newNotificationAction(actionText:"Open",callback:openSignal(signalEventFromCloud[i]),payload:"Opensignal")回调函数为:openSignal(Signalsignal){Navigator.push(context,newMaterialPageRoute(builder:(context)=>newDetailSc