java - 获取 gridPane 中的按钮并使用 javaFx 更改其文本

Question

我试图在我的 Controller 类中获取 gridPane 的所有成员(它们是按钮)，但我遇到了异常，您可以在下面看到它:

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 self 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 应该对此发出警告。但你应该使用

GridPane.getRowIndex(node)

不是

grid.getRowIndex(node)

等等

<小时/>

方法GridPane.getRowIndex(Node)和 GridPane.getColumnIndex(node)返回一个包装Integer对象，而不是原始int。因此，当您使用 == 按身份进行比较时，您隐式地使用了拆箱。换句话说，您的代码相当于

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

如果添加到网格 Pane 的任何节点未指定行索引和列索引，则 GridPane.getRowIndex(...) 或 GridPane.getColumnIndex(...) 将返回 null，因此您将隐式尝试对 null 引用调用 intValue()，从而导致空指针异常。请注意，如果您调用了grid.setGridLinesVisible(true);，这会导致GridPane添加一个未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，这样您就可以访问它们而无需所有迭代，但我想这只是一个风格问题。