Question

我试图在我的控制器类中获取gridPane的所有成员（它们是按钮），但我得到例外，你可以在下面看到它：

Exception in Application start methodjava.lang.reflect.InvocationTargetException
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:497)
at com.sun.javafx.application.LauncherImpl.launchApplicationWithArgs(LauncherImpl.java:389)
at com.sun.javafx.application.LauncherImpl.launchApplication(LauncherImpl.java:328)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:497)
at sun.launcher.LauncherHelper$FXHelper.main(LauncherHelper.java:767) 
Caused by: java.lang.RuntimeException: Exception in Application start method
    at com.sun.javafx.application.LauncherImpl.launchApplication1(LauncherImpl.java:917)
    at com.sun.javafx.application.LauncherImpl.lambda$launchApplication$152(LauncherImpl.java:182)
    at com.sun.javafx.application.LauncherImpl$$Lambda$51/1263764.run(Unknown Source)
    at java.lang.Thread.run(Thread.java:745)
Caused by: javafx.fxml.LoadException: 
file:/C:/Users/Family/Documents/NetBeansProjects/FarsiCallender/dist/run1583526066/FarsiCallender.jar!/farsicallender/FXMLDocument.fxml
at javafx.fxml.FXMLLoader.constructLoadException(FXMLLoader.java:2605)
at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2583)
at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2445)
at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3218)
at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3179)
at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3152)
at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3128)
at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3108)
at javafx.fxml.FXMLLoader.load(FXMLLoader.java:3101)
at farsicallender.FarsiCallender.start(FarsiCallender.java:29)
at com.sun.javafx.application.LauncherImpl.lambda$launchApplication1$159(LauncherImpl.java:863)
at com.sun.javafx.application.LauncherImpl$$Lambda$54/4239053.run(Unknown Source)
at com.sun.javafx.application.PlatformImpl.lambda$runAndWait$172(PlatformImpl.java:326)
at com.sun.javafx.application.PlatformImpl$$Lambda$47/20085625.run(Unknown Source)
at com.sun.javafx.application.PlatformImpl.lambda$null$170(PlatformImpl.java:295)
at com.sun.javafx.application.PlatformImpl$$Lambda$49/3796086.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at com.sun.javafx.application.PlatformImpl.lambda$runLater$171(PlatformImpl.java:294)
at com.sun.javafx.application.PlatformImpl$$Lambda$48/2900468.run(Unknown Source)
at com.sun.glass.ui.InvokeLaterDispatcher$Future.run(InvokeLaterDispatcher.java:95)
at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
at com.sun.glass.ui.win.WinApplication.lambda$null$145(WinApplication.java:101)
at com.sun.glass.ui.win.WinApplication$$Lambda$37/17230114.run(Unknown Source)
... 1 more
Caused by: java.lang.NullPointerException
    at farsicallender.FXMLDocumentController.setDays(FXMLDocumentController.java:249)
    at farsicallender.FXMLDocumentController.initialize(FXMLDocumentController.java:181)
    at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2552)
    ... 22 more
Exception running application farsicallender.FarsiCallender
Java Result: 1

这个异常来自我的代码的这一部分，在检查我的代码之前你必须知道我有一个gridPane（6 * 7），这是我的代码：

for (int i = 0; i < 6; i++) {
     for (int j = 0; j < 7; j++) {
         for (Node node : grid.getChildren()) {
             if (grid.getRowIndex(node) == i && grid.getColumnIndex(node) == j) {
                  Button b = (Button)node;
                  b.setText(ar[i][j]+"");
                  System.out.println("z:" + i+" "+j);
                  break;
             }
         }
     }
}

第249行是：

if (grid.getRowIndex(node) == i && grid.getColumnIndex(node) == j) {

Answer 1

顺便说一句，您不应该从非静态上下文中调用静态方法。您的IDE应该警告您这一点。但你应该使用

GridPane.getRowIndex(node)

不

grid.getRowIndex(node)

等

方法GridPane.getRowIndex(Node)和GridPane.getColumnIndex(node)返回包装器Integer对象，而不是原始int。因此，当您使用==按身份进行比较时，您隐式使用取消装箱。换句话说，您的代码等同于

if (GridPane.getRowIndex(node).intValue() == i 
  && GridPane.getColumnIndex(node).intValue() == j) { ... }

如果在没有指定行索引和列索引的情况下向网格窗格添加了任何节点，则GridPane.getRowIndex(...)或GridPane.getColumnIndex(...)将返回null，因此您将隐式尝试调用intValue()在null引用上，导致空指针异常。请注意，如果您调用了grid.setGridLinesVisible(true);，则会导致GridPane添加一个没有设置行索引或列索引的节点。

因此，快速解决此问题的方法是进行空检查：

Integer rowIndex = GridPane.getRowIndex(node);
Integer columnIndex = GridPane.getColumnIndex(node);

if (rowIndex != null && rowIndex.intValue() == i
  && columnIndex != null && columnIndex.intValue() == j) {

    // ...
}

我可能更喜欢组织代码，以便将按钮保存在一个数组中，这样你就可以在没有所有迭代的情况下访问它们，但我想这只是风格问题。

获取gridPane中的按钮并使用javaFx更改其文本

1 个答案: