英文:
Problem with clicking on favorite item in RecyclerView
问题
我正尝试使用Volley库和JSON创建一个RSS新闻订阅应用程序，基于RecyclerView，其中每行包含标题、发布日期、描述和文章链接。
该应用程序应允许创建一个收藏夹文章列表（数据库）。
当我使用占位信息而不是真实的互联网内容运行应用程序时，一切正常。
但当我连接到互联网并点击“收藏”按钮（心形按钮）时，出现以下错误：
[从互联网加载的信息][1]
[错误消息][2]
以下是相关代码的部分，其中包含突出显示的行和调试日志：
public BbsNewsViewHolder(@NonNull View itemView){
super(itemView);
titleTextView = itemView.findViewById(R.id.txtTitle);
pubDateTextView= itemView.findViewById(R.id.txtPubDate);
descriptionTextView=itemView.findViewById(R.id.txtDescription);
linkTextView = itemView.findViewById(R.id.link);
favBtn = itemView.findViewById(R.id.favBtn);
//添加到收藏夹
favBtn.setOnClickListener(new View.OnClickListener(){
@Override
public void onClick(View view){
int position = getAdapterPosition();
ArticleItem articleItem = articleItems.get(position);
if (articleItem.getFavStatus().equals("0")) {
articleItem.setFavStatus("1");
favDB.insertIntoTheDatabase(articleItem.getTitle(),
articleItem.getPubDate(),
articleItem.getDescription(),
articleItem.getWebUrl(),
articleItem.getKey_id(),
articleItem.getFavStatus());
favBtn.setBackgroundResource(R.drawable.ic_favorite_color);
} else {
articleItem.setFavStatus("0");
favDB.remove_fav(articleItem.getKey_id());
favBtn.setBackgroundResource(R.drawable.ic_favorite_border);
}
}
});
}
错误日志：
04/06 16:29:34: 在 Nexus 4 API 23 上启动'app'。
$ adb shell am start -n "com.example.favoritelist/com.example.favoritelist.MainActivity" -a android.intent.action.MAIN -c android.intent.category.LAUNCHER -D
等待应用程序上线：com.example.favoritelist.test | com.example.favoritelist
等待应用程序上线：com.example.favoritelist.test | com.example.favoritelist
等待应用程序上线：com.example.favoritelist.test | com.example.favoritelist
连接到 com.example.favoritelist
已连接到目标虚拟机，地址：'localhost:8628'，传输：'socket'
捕获并显示应用程序的日志消息。可以在“调试器”设置页面的“Logcat输出”部分中禁用此行为。
I/art: 调试器已启动
I/System.out: 调试器已连接
等待调试器稳定...
I/System.out: 等待调试器稳定...
I/System.out: 等待调试器稳定...
I/System.out: 等待调试器稳定...
I/System.out: 等待调试器稳定...
I/System.out: 等待调试器稳定...
I/System.out: 等待调试器稳定...
I/System.out: 调试器已稳定（1495）
W/System: 类加载器引用了未知路径：/data/app/com.example.favoritelist-2/lib/x86
W/FirebaseApp：默认FirebaseApp初始化失败，因为未找到默认选项。这通常意味着 com.google.gms:google-services 没有应用于您的 gradle 项目。
I/FirebaseInitProvider：FirebaseApp 初始化失败
W/art：Android 4.1 之前，在 android.graphics.drawable 中的方法 android.graphics.PorterDuffColorFilter androidx.vectordrawable.graphics.drawable.VectorDrawableCompat.updateTintFilter(android.graphics.PorterDuffColorFilter, android.content.res.ColorStateList, android.graphics.PorterDuff$Mode) 将错误地覆盖 android.graphics.drawable.Drawable 中的 package-private 方法
I/art：拒绝对先前失败的类 java.lang.Class<androidx.core.view.ViewCompat$2> 进行重新初始化
I/art：拒绝对先前失败的类 java.lang.Class<androidx.core.view.ViewCompat$2> 进行重新初始化
D/OpenGLRenderer：使用 EGL_SWAP_BEHAVIOR_PRESERVED：true
D/：HostConnection::get() 已建立新的主机连接 0xb3fefd40，tid 6001
D/：HostConnection::get() 已建立新的主机连接 0xa1cff240，tid 6040
I/OpenGLRenderer：已初始化 EGL，版本 1.4
W/OpenGLRenderer：选择带有 EGL_SWAP_BEHAVIOR_PRESERVED 的配置失败，正在重试...
D/EGL_emulation：eglCreateContext：0xae6b45c0：maj 3 min 1 rcv 4
D/EGL_emulation：eglMakeCurrent：0xae6b45c0：ver 3 1（tinfo 0xb2a145c0）
E/eglCodecCommon：glUtilsParamSize：未知参数 0x000082da
glUtilsParamSize：未知参数 0x00008cdf
E/eglCodecCommon：glUtilsParamSize：未知参数 0x00008824
D/EGL_emulation：eglMakeCurrent：0xae6b45c0：ver 3 1（tinfo 0xb2a145c0）
D/AndroidRuntime：关闭 VM
E/AndroidRuntime：致命异常：主线程
处理程序：com.example.favoritelist，PID：6001
java.lang.NullPointerException：尝试调用虚拟方法 'boolean java.lang.String.equals(java.lang.Object)'，但空对象引用
在 com.example.favoritelist.ArticleAdapter$BbsNewsViewHolder$1.onClick(ArticleAdapter.java:89) 处
在 android.view.View.performClick(View.java:5198) 处
在 android.view.View$PerformClick.run(View.java:21147) 处
在 android.os.Handler.handleCallback(Handler.java:739) 处
在 android.os.Handler.dispatchMessage(Handler.java:95) 处
在 android.os.Looper.loop(Looper.java:148) 处
在 android.app.ActivityThread.main(ActivityThread.java:5417) 处
在 java.lang.reflect.Method.invoke(Native Method) 处
在 com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726) 处
在 com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616) 处
I/Process：发送信号。PID：6001 SIG：9
已从目标虚拟机断开连接，地址：
<details>
<summary>英文:</summary>
I’m trying to create rss news feeding app using Volley library/JSON with on the base of RecyclerView, where each row contains title, pubdate, description and link to the Article.
This app should allow to create a list of favorite articles(DB).
When I run the app with placeholder info instead of real internet content, everything works OK.
But when I run it with internet connection and click on the “favorite ” button(heart), the following error appears:
[loaded info from internet][1]
[error message][2]
Below is the part of the related code with highlighted line and debug log:
public BbsNewsViewHolder(@NonNull View itemView){
super(itemView);
titleTextView = itemView.findViewById(R.id.txtTitle);
pubDateTextView= itemView.findViewById(R.id.txtPubDate);
descriptionTextView=itemView.findViewById(R.id.txtDescription);
linkTextView = itemView.findViewById(R.id.link);
favBtn = itemView.findViewById(R.id.favBtn);
//add to favorites
favBtn.setOnClickListener(new View.OnClickListener(){
@Override
public void onClick(View view){
int position = getAdapterPosition();
ArticleItem articleItem = articleItems.get(position);
if (articleItem.getFavStatus().equals("0")) {
articleItem.setFavStatus("1");
favDB.insertIntoTheDatabase(articleItem.getTitle(),
articleItem.getPubDate(),
articleItem.getDescription(),
articleItem.getWebUrl(),
articleItem.getKey_id(),
articleItem.getFavStatus());
favBtn.setBackgroundResource(R.drawable.ic_favorite_color);
} else {
articleItem.setFavStatus("0");
favDB.remove_fav(articleItem.getKey_id());
favBtn.setBackgroundResource(R.drawable.ic_favorite_border);
}
}
});
}
Error Log:
04/06 16:29:34: Launching 'app' on Nexus 4 API 23.
$ adb shell am start -n "com.example.favoritelist/com.example.favoritelist.MainActivity" -a android.intent.action.MAIN -c android.intent.category.LAUNCHER -D
Waiting for application to come online: com.example.favoritelist.test | com.example.favoritelist
Waiting for application to come online: com.example.favoritelist.test | com.example.favoritelist
Waiting for application to come online: com.example.favoritelist.test | com.example.favoritelist
Connecting to com.example.favoritelist
Connected to the target VM, address: 'localhost:8628', transport: 'socket'
Capturing and displaying logcat messages from application. This behavior can be disabled in the "Logcat output" section of the "Debugger" settings page.
I/art: Debugger is active
I/System.out: Debugger has connected
waiting for debugger to settle...
I/System.out: waiting for debugger to settle...
I/System.out: waiting for debugger to settle...
I/System.out: waiting for debugger to settle...
I/System.out: waiting for debugger to settle...
I/System.out: waiting for debugger to settle...
I/System.out: waiting for debugger to settle...
I/System.out: debugger has settled (1495)
W/System: ClassLoader referenced unknown path: /data/app/com.example.favoritelist-2/lib/x86
W/FirebaseApp: Default FirebaseApp failed to initialize because no default options were found. This usually means that com.google.gms:google-services was not applied to your gradle project.
I/FirebaseInitProvider: FirebaseApp initialization unsuccessful
W/art: Before Android 4.1, method android.graphics.PorterDuffColorFilter androidx.vectordrawable.graphics.drawable.VectorDrawableCompat.updateTintFilter(android.graphics.PorterDuffColorFilter, android.content.res.ColorStateList, android.graphics.PorterDuff$Mode) would have incorrectly overridden the package-private method in android.graphics.drawable.Drawable
I/art: Rejecting re-init on previously-failed class java.lang.Class<androidx.core.view.ViewCompat$2>
I/art: Rejecting re-init on previously-failed class java.lang.Class<androidx.core.view.ViewCompat$2>
D/OpenGLRenderer: Use EGL_SWAP_BEHAVIOR_PRESERVED: true
D/: HostConnection::get() New Host Connection established 0xb3fefd40, tid 6001
D/: HostConnection::get() New Host Connection established 0xa1cff240, tid 6040
I/OpenGLRenderer: Initialized EGL, version 1.4
W/OpenGLRenderer: Failed to choose config with EGL_SWAP_BEHAVIOR_PRESERVED, retrying without...
D/EGL_emulation: eglCreateContext: 0xae6b45c0: maj 3 min 1 rcv 4
D/EGL_emulation: eglMakeCurrent: 0xae6b45c0: ver 3 1 (tinfo 0xb2a145c0)
E/eglCodecCommon: glUtilsParamSize: unknow param 0x000082da
glUtilsParamSize: unknow param 0x00008cdf
E/eglCodecCommon: glUtilsParamSize: unknow param 0x00008824
D/EGL_emulation: eglMakeCurrent: 0xae6b45c0: ver 3 1 (tinfo 0xb2a145c0)
D/AndroidRuntime: Shutting down VM
E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.favoritelist, PID: 6001
java.lang.NullPointerException: Attempt to invoke virtual method 'boolean java.lang.String.equals(java.lang.Object)' on a null object reference
at com.example.favoritelist.ArticleAdapter$BbsNewsViewHolder$1.onClick(ArticleAdapter.java:89)
at android.view.View.performClick(View.java:5198)
at android.view.View$PerformClick.run(View.java:21147)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
I/Process: Sending signal. PID: 6001 SIG: 9
Disconnected from the target VM, address: 'localhost:8628', transport: 'socket'
[1]: https://i.stack.imgur.com/JDvDe.jpg
[2]: https://i.stack.imgur.com/tq37X.png
</details>
# 答案1
**得分**: 0
如果您注意到，您在以下日志中遇到了`NullPointException`：
> `java.lang.NullPointerException: 尝试在空对象引用上调用虚拟方法'boolean java.lang.String.equals(java.lang.Object)'`
因此，此异常的原因是您在`String`对象上调用了`.equals()`方法。回顾您的代码；您仅在`articleItem.getFavStatus().equals("0")`中使用了`.equals()`。
所以，显然您的`articleItem.getFavStatus()`是一个空值，并且您试图将其与"0"进行比较。因此，您需要检查为什么它返回为空，还可以将此代码部分包装在`try`块中，或者在此语句处设置断点以进行检查。
希望对您有所帮助。
<details>
<summary>英文:</summary>
If you notice, you got `NullPointException` with the following log:
> `java.lang.NullPointerException: Attempt to invoke virtual method 'boolean java.lang.String.equals(java.lang.Object)' on a null object reference`
So, the cause of this exception that you call `.equals()` method on a `String` object. Looking back into your code; you used `.equals()` only once in `articleItem.getFavStatus().equals("0")`.
So, obviously your `articleItem.getFavStatus()` is a null value and you are trying to compare it to "0". So, you need to check why it returns null, also you can wrap this part of code into a `try` block, or put a break point at this statement to examine it.
hope that help you out.
</details>
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