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NullPointerException：Attempt to Invoke a Method on a Null Object Reference

NullPointerException：Attempt to Invoke a Method on a Null Object Reference ✨ 摘要大家好，我是默语，今天我们要深入探讨Java...NPE的成因与原理什么是null？在Java中，null是一个特殊的字面量，它表示一个对象的“缺失”或“空值”。当一个变量被初始化为null时，它并不指向任何对象的内存位置。...避免显式赋值null 在代码中尽量避免显式将变量设置为null，可以使用默认值或空对象模式来代替。...# NullPointerException：Attempt to Invoke a Method on a Null Object Reference ✨ 摘要大家好，我是默语，今天我们要深入探讨Java...NPE的成因与原理什么是null？在Java中，null是一个特殊的字面量，它表示一个对象的“缺失”或“空值”。当一个变量被初始化为null时，它并不指向任何对象的内存位置。

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org.apache.ibatis.binding.BindingException: Mapper method attempted to return null from a method wi

一、问题描述今天发现测试环境报出来一个数据库相关的错误 org.apache.ibatis.binding.BindingException: Mapper method 'attempted to...return null from a method with a primitive return type (long)....Long可以为null，但基本类型long则不可以被赋值null。...当然是不可以的 Long a = null; long b = a; 因为会报java.lang.NullPointerException，而框架报出来的就是attempted to return null...from a method with a primitive return type (long) 三、解决方案方案一：将返回类型修改为Long就可以了，并在对应的Service层做相应的判断就可以了

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NullPointerException：Attempt to Invoke a Method on a Null Object Reference完美解决方法

NullPointerException：Attempt to Invoke a Method on a Null Object Reference完美解决方法摘要大家好，我是默语！...今天我们将深入探讨 Java 中的 NullPointerException 异常，特别是“Attempt to invoke a method on a null object reference”的错误...// 试图调用 null 对象的方法 System.out.println(str.length()); } } 在这个示例中，str 为 null，调用 str.length(...在访问对象前进行 null 检查，避免对 null 对象进行操作。使用 Optional 类来处理可能为 null 的值，提升代码的可读性和安全性。...根据异常发生的具体场景，添加 null 检查或重构代码以避免对 null 对象的操作。

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NullPointerException : Attempt to invoke a method on a null object reference 完美解决方法

NullPointerException : Attempt to invoke a method on a null object reference 完美解决方法摘要大家好，我是默语。...null可能会导致NPE。...} 2.3 操作返回null的函数结果当函数返回值可能为null时，直接操作其结果也是引发NPE的常见场景。...= null) { System.out.println(str.length()); } 3.2 使用Optional来防止null Java 8引入了Optional类，可以有效避免null...null } 4.

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laravel项目出现Non-static method Redis::hGet() cannot be called statically的解决方法

早上ytkah在配置laravel项目中出现Non-static method Redis::hGet() cannot be called statically错误提示，很显然这是redis出问题了

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org.apache.ibatis.binding.BindingException: Mapper method ... attempted to return null from a m...

FIX: org.apache.ibatis.binding.BindingException: Mapper method 'com.alibaba.swork.info.common.mapper.QualityDataOfTeamMapper.getAvgIssueFixedDuration...attempted to return null from a method with a primitive return type (double).

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【错误记录】Flutter 构建报错 ( Error: Method not found: ‘CupertinoModalPopupRoute‘. | 下载最新 Flutter SDK 版本 )

文章目录一、报错信息二、问题分析三、解决方案一、报错信息 ---- 参考【Flutter】Flutter Gallery 官方示例简介博客 ; Flutter Galley 开源项目运行时...Running Gradle task 'assembleDebug'... lib/demos/cupertino/cupertino_alert_demo.dart:240:12: Error: Method...* Where: Script 'Y:\001_DevelopTools\010_Flutter\flutter_windows_2.0.2-stable\flutter\packages\flutter_tools...'. > Process 'command 'Y:\001_DevelopTools\010_Flutter\flutter_windows_2.0.2-stable\flutter\bin\flutter.bat...-12.2.pre 版本的 Flutter SDK ; flutter_windows_2.1.0-12.2.pre-beta.zip 下载后解压上述 SDK 压缩包 flutter_windows_

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【错误记录】Android 编译报错 ( Attempt to invoke virtual method ‘void xx.ActionBar.setTitle()‘ on a null obj )

cn.zkhw.client.BottomNavigationActivity}: java.lang.NullPointerException: Attempt to invoke virtual method...'void androidx.appcompat.app.ActionBar.setTitle(java.lang.CharSequence)' on a null object reference...(Native Method) at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java...'void androidx.appcompat.app.ActionBar.setTitle(java.lang.CharSequence)' on a null object reference...'void androidx.appcompat.app.ActionBar.setTitle(java.lang.CharSequence)' on a null object reference

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【Flutter】Flutter 混合开发 ( Flutter 与 Native 通信 | Android 端实现 MethodChannel 通信 )

) { Log.e(TAG, "Parameter messenger must not be null."); } if (name == null) {...Log.e(TAG, "Parameter name must not be null."); } if (codec == null) { Log.e(TAG,...* * The handler is called on the platform thread (Android main thread)....MethodChannel}. */ public final class MethodCall { /** The name of the called method. */ public final...* * All methods of this class must be called on the platform thread (Android main thread).

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flutter weight demo

flutter sdk:快速下载：https://github.com/flutter/flutter/releases 翻译: StatelessWidget 无状态小部件...由于flutter_app2依赖于flutter_test任何不存在的sdk（flutter sdk不可用），版本求解失败。...If we changed _counter without calling // setState(), then the build method would not be called...every time setState is called, for instance // as done by the _increment method above. // The...argument_type_not_assignable leading: new IconButton( icon: new Icon(Icons.menu), onPressed: null

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Flutter Notification使用说明

Flutter Notification 使用说明概述在Flutter进行界面开发时，我们经常会遇到数据传递的问题。由于Flutter采用节点树的方式组织页面，以致于一个普通页面的节点层级会很深。...所幸，Flutter的Notification为我们提供了这样的能力。.../// Calling this method is relatively expensive (O(N) in the depth of the tree). /// /// This method.... /// /// The notification's [Notification.visitAncestor] method is called for each /// ancestor...以上就是Flutter中Notification的基本原理和使用方法。

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Flutter ServicesBinding.defaultBinaryMessenger was accessed before the binding was initialized.

()` has been called (for example, during plugin initialization), then you need to explicitly call the...()` as the first line in your test's `main()` method to initialize the binding....If you're running an application and need to access the binary messenger before `runApp()` has been called...initialized, then /// it will at least implement [WidgetsBinding]. /// /// You only need to call this method...static WidgetsBinding ensureInitialized() { if (WidgetsBinding.instance == null) WidgetsFlutterBinding

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那些初学者实践 Flutter 最常出现的错误

典型错误一：无法掌握的Future 典型错误信息：NoSuchMethodError: The method 'markNeedsBuild' was called on null....典型错误二：Navigator.of(context) 是个 null 典型错误信息：NoSuchMethodError: The method 'pop' was called on null....典型错误信息： Failed assertion: boolean expression must not be null NoSuchMethodError: The method '>' was called...NoSuchMethodError: The method '+' was called on null....NoSuchMethodError: The method '*' was called on null. 示例代码这种错误，较常发生在使用服务端返回的数据model时。

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纯Flutter工程如何实现Flutter与原生互相通信

", null); } } else {...'; FutureNull> _getBatteryLevel() async { String batteryLevel; try { final int result...== "onLoginSuccess") { userInfoNotifier.getUserInfo(); } else if (call.method == "onAuthSuccess...都应该是这个 BinaryMessenger get defaultBinaryMessenger { assert(() { if (ServicesBinding.instance == null...running an application and need to access the binary " 'messenger before `runApp()` has been called

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认识MethodChannel

= null), assert(binaryMessenger != null), assert(codec !...(MethodCall(method, arguments)), ); if (result == null) { throw MissingPluginException(...'No implementation found for method $method on channel $name'); } final T typedResult = codec.decodeEnvelope...this.isAttached()) { Log.d("FlutterView", "FlutterView.send called on a detached view, channel...this.isAttached()) { Log.d("FlutterNativeView", "FlutterView.send called on a detached view,

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【Flutter 专题】81 图解 Android Native 集成 FlutterBoost 小尝试 (三)

发现有些手机进退两次应用就会崩溃，和尚也是很崩溃，抓到 Log 提示 Surface 在销毁时空指针； java.lang.NullPointerException: Attempt to invoke virtual method...'void android.view.Surface.release()' on a null object reference at io.flutter.embedding.android.FlutterTextureView.disconnectSurfaceFromRenderer...Looper.java:154) at android.app.ActivityThread.main(ActivityThread.java:5527) at java.lang.reflect.Method.invoke...(Native Method) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:739...) { throw new IllegalStateException("disconnectSurfaceFromRenderer() should only be called when

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Flutter Chanel通信流程

static const method = const MethodChannel('com.ycbjie.android/method'); 添加监听NA调用flutter方法的监听，flutter代码是...eventSink = events Log.d("Android", "EventChannel onListen called...{ Log.w("Android", "EventChannel onCancel called") }...( name, codec.encodeMethodCall(new MethodCall(method, arguments)), callback == null ?...method, { bool missingOk, dynamic arguments }) async { assert(method !

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【Flutter 专题】49 图解 Flutter 与 Android 原生交互

=null?...=null?...中传递的相同 method name 时可以尝试获取传递参数；若此时需要向 Flutter 返回传递参数可以通过 result.success() 方法进行数据传递，若无需传递则可不设置当前方法；...=null?...注意事项 1. ensureInitializationComplete must be called after startInitialization 和尚在从 Android 到 Flutter

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从JNI_OnLoad看so的加载

= Looper.getMainLooper()) { throw new IllegalStateException("startInitialization must be called...on the main thread"); } else if (sSettings == null) { sSettings = settings; long...") 进行 flutter 的 so 加载。...(Runtime, freeMemory, "()J"), FAST_NATIVE_METHOD(Runtime, totalMemory, "()J"), FAST_NATIVE_METHOD...(Runtime, maxMemory, "()J"), NATIVE_METHOD(Runtime, gc, "()V"), NATIVE_METHOD(Runtime, nativeExit

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Dart和Java通信源码分析和实践

codec.encodeMethodCall(MethodCall(method, arguments)), ); if (result == null) { throw MissingPluginException..., [this.arguments]): assert(method !...= null); final String method; final dynamic arguments; @override String toString() => '$runtimeType...为io/flutter/embedding/engine/FlutterJNI g_handle_platform_message_method = env->GetMethodID.../embedding/engine/FlutterJNI.java // Called by native. // TODO(mattcarroll): determine if message is

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NullPointerException：Attempt to Invoke a Method on a Null Object Reference

org.apache.ibatis.binding.BindingException: Mapper method attempted to return null from a method wi

NullPointerException：Attempt to Invoke a Method on a Null Object Reference完美解决方法

NullPointerException : Attempt to invoke a method on a null object reference 完美解决方法

laravel项目出现Non-static method Redis::hGet() cannot be called statically的解决方法

org.apache.ibatis.binding.BindingException: Mapper method ... attempted to return null from a m...

【错误记录】Flutter 构建报错 ( Error: Method not found: ‘CupertinoModalPopupRoute‘. | 下载最新 Flutter SDK 版本 )

【错误记录】Android 编译报错 ( Attempt to invoke virtual method ‘void xx.ActionBar.setTitle()‘ on a null obj )

【Flutter】Flutter 混合开发 ( Flutter 与 Native 通信 | Android 端实现 MethodChannel 通信 )

flutter weight demo

Flutter Notification使用说明

Flutter ServicesBinding.defaultBinaryMessenger was accessed before the binding was initialized.

那些初学者实践 Flutter 最常出现的错误

纯Flutter工程如何实现Flutter与原生互相通信

认识MethodChannel

【Flutter 专题】81 图解 Android Native 集成 FlutterBoost 小尝试 (三)

Flutter Chanel通信流程

【Flutter 专题】49 图解 Flutter 与 Android 原生交互

从JNI_OnLoad看so的加载

Dart和Java通信源码分析和实践

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