尝试调用虚方法'int java.lang.String.hashCode()'

Question

我正在尝试使用Volley Library将URL中的图像加载到girdview中.为此,我正在学习本教程.当我运行我的项目时,它从服务器数据库收集所有URL,然后存储在arraylist中.但是不显示图像.我收到了java.lang.NullPointerException: Attempt to invoke virtual method 'int java.lang.String.hashCode()' on a null object reference错误.它甚至没有指向我遇到此错误的任何代码行数.见下面Logcat输出:

java.lang.NullPointerException: Attempt to invoke virtual method 'int java.lang.String.hashCode()' on a null object reference
        at com.android.volley.Request.<init>(Request.java:136)
        at com.android.volley.toolbox.ImageRequest.<init>(ImageRequest.java:71)
        at com.android.volley.toolbox.ImageLoader.get(ImageLoader.java:219)
        at com.android.volley.toolbox.ImageLoader.get(ImageLoader.java:171)
        at com.android.volley.toolbox.NetworkImageView.loadImageIfNecessary(NetworkImageView.java:141)
        at com.android.volley.toolbox.NetworkImageView.onLayout(NetworkImageView.java:190)
        at android.view.View.layout(View.java:15596)
        at android.widget.FrameLayout.layoutChildren(FrameLayout.java:573)
        at android.widget.FrameLayout.onLayout(FrameLayout.java:508)
        at android.view.View.layout(View.java:15596)
        at android.view.ViewGroup.layout(ViewGroup.java:4966)
        at android.widget.GridView.setupChild(GridView.java:1542)
        at android.widget.GridView.makeAndAddView(GridView.java:1436)
        at android.widget.GridView.makeRow(GridView.java:361)
        at android.widget.GridView.fillDown(GridView.java:302)
        at android.widget.GridView.fillFromTop(GridView.java:437)
        at android.widget.GridView.layoutChildren(GridView.java:1276)
        at android.widget.AbsListView.onLayout(AbsListView.java:2148)
        at android.view.View.layout(View.java:15596)
        at android.view.ViewGroup.layout(ViewGroup.java:4966)
        at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1703)
        at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1557)
        at android.widget.LinearLayout.onLayout(LinearLayout.java:1466)
        at android.view.View.layout(View.java:15596)
        at android.view.ViewGroup.layout(ViewGroup.java:4966)
        at android.widget.FrameLayout.layoutChildren(FrameLayout.java:573)
        at android.widget.FrameLayout.onLayout(FrameLayout.java:508)
        at android.widget.ScrollView.onLayout(ScrollView.java:1502)
        at android.view.View.layout(View.java:15596)
        at android.view.ViewGroup.layout(ViewGroup.java:4966)
        at android.widget.FrameLayout.layoutChildren(FrameLayout.java:573)
        at android.widget.FrameLayout.onLayout(FrameLayout.java:508)
        at android.view.View.layout(View.java:15596)
        at android.view.ViewGroup.layout(ViewGroup.java:4966)
        at com.android.internal.widget.ActionBarOverlayLayout.onLayout(ActionBarOverlayLayout.java:494)
        at android.view.View.layout(View.java:15596)
        at android.view.ViewGroup.layout(ViewGroup.java:4966)
        at android.widget.FrameLayout.layoutChildren(FrameLayout.java:573)
        at android.widget.FrameLayout.onLayout(FrameLayout.java:508)
        at android.view.View.layout(View.java:15596)
        at android.view.ViewGroup.layout(ViewGroup.java:4966)
        at android.view.ViewRootImpl.performLayout(ViewRootImpl.java:2072)
        at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1829)
        at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1054)
        at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:5779)
        at android.view.Choreographer$CallbackRecord.run(Choreographer.java:767)
        at android.view.Choreographer.doCallbacks(Choreographer.java:580)
        at android.view.Choreographer.doFrame(Choreographer.java:550)
        at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:753)
        at android.os.Handler.handleCallback(Handler.java:739)
        at android.os.Handler.dispatchMessage(Handler.java:95)
        at android.os.Looper.loop(Looper.java:135)
        at android.app.ActivityThread.main(ActivityThread.java:5221)
        at java.lang.reflect.Method.invoke(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:372)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)

任何人都可以帮我解决确切的问题,我该如何解决这个问题？

Answer 1

您应该检查从服务器获取数据的映像的空值.

Answer 2

在尝试从数据类的片段中将 URL 加载到 webview 客户端时，我遇到了同样的错误。
我编写了自己的 hashcode 函数实现来检查 API 的 null 或空响应。
这是实现。

data class Article(

    @PrimaryKey(autoGenerate = true)
    var id: Int? = null,

    val author: String,
    val content: String,
    val description: String,
    val publishedAt: String,
    val source: Source,
    val title: String,
    val url: String,
    val urlToImage: String
) : Serializable{

    override fun hashCode(): Int {
        var result = id.hashCode()
      if(url.isNullOrEmpty()){
          result = 31 * result + url.hashCode()
      }
        return result
    }
}

Answer 3

获取字符串值为 null，在此实例中显示 String.hashcode() 错误