如何检查textfield是否为空？ [英] How to check if textfield is empty?
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问题描述
对于我的JavaFx应用程序我想检查TextFields是否为空，如果是，则提醒用户。
这些是TextFields：
for my JavaFx application I want to check if the TextFields are empty, and if so, alert the user. These are the TextFields:
VBox fields = new VBox();
Text usernametext = new Text("User name");
TextField user_name = new TextField();
Text firstnametext = new Text("First name");
TextField first_name = new TextField();
Text lastnametext = new Text("Last name");
TextField last_name = new TextField();
Text ibantext = new Text("IBAN");
TextField iban = new TextField();
Text passwordtext = new Text("Password");
TextField password = new TextField();
Text confirmpasstext = new Text("Confirm password");
TextField confirmpass = new TextField();
Button createBtn = new Button("Create account");
现在我只想在一个文本字段上测试验证。这是我的验证函数，链接到createBtn：
for now i just wanted to test the validation on one textfield. this is my validation function that is linked to the createBtn:
public void validation(){
if(user_name.getText().trim().isEmpty()){
Alert fail= new Alert(AlertType.INFORMATION);
fail.setHeaderText("failure");
fail.setContentText("you havent typed something");
fail.showAndWait();
} else {
Alert alert = new Alert(AlertType.INFORMATION);
alert.setHeaderText("Succes");
alert.setContentText("Account succesfully created!");
alert.showAndWait();
}
}
但我收到此错误消息，因为我按'创建帐户'按钮：
But I get this error message as i press the 'Create Account' button:
Exception in thread "JavaFX Application Thread"
java.lang.NullPointerException
at opdracht1.Opdracht1.validation(Opdracht1.java:36)
at opdracht1.Opdracht1$2$1.handle(Opdracht1.java:103)
at opdracht1.Opdracht1$2$1.handle(Opdracht1.java:98)
at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:86)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:49)
at javafx.event.Event.fireEvent(Event.java:198)
at javafx.scene.Node.fireEvent(Node.java:8411)
at javafx.scene.control.Button.fire(Button.java:185)
at com.sun.javafx.scene.control.behavior.ButtonBehavior.mouseReleased(ButtonBehavior.java:182)
at com.sun.javafx.scene.control.skin.BehaviorSkinBase$1.handle(BehaviorSkinBase.java:96)
at com.sun.javafx.scene.control.skin.BehaviorSkinBase$1.handle(BehaviorSkinBase.java:89)
at com.sun.javafx.event.CompositeEventHandler$NormalEventHandlerRecord.handleBubblingEvent(CompositeEventHandler.java:218)
at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:80)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:54)
at javafx.event.Event.fireEvent(Event.java:198)
at javafx.scene.Scene$MouseHandler.process(Scene.java:3757)
at javafx.scene.Scene$MouseHandler.access$1500(Scene.java:3485)
at javafx.scene.Scene.impl_processMouseEvent(Scene.java:1762)
at javafx.scene.Scene$ScenePeerListener.mouseEvent(Scene.java:2494)
at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:352)
at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:275)
at java.security.AccessController.doPrivileged(Native Method)
at com.sun.javafx.tk.quantum.GlassViewEventHandler.lambda$handleMouseEvent$355(GlassViewEventHandler.java:388)
at com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(QuantumToolkit.java:389)
at com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:387)
at com.sun.glass.ui.View.handleMouseEvent(View.java:555)
at com.sun.glass.ui.View.notifyMouse(View.java:937)
at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
at com.sun.glass.ui.win.WinApplication.lambda$null$149(WinApplication.java:191)
at java.lang.Thread.run(Thread.java:745)
提前致谢！
推荐答案
首先，检查 user_name 是否 null 。如果不是，则在代码中的某处将 null 文本值设置为JavaFX组件。
First of all, check if user_name is not null. If it is not, you are setting a null text value to the JavaFX component somewhere in your code.
if（user_name.getText（）。trim（）。isEmpty（））{
在任何情况下，将 trim（）应用于 null 值都会导致您的异常。您不应该需要这个（请参阅 Uluk Biy 对此答案的评论），但考虑到您创建了 user_name TextField，您必须先检查 getText（）方法不是 null 。
In any case, applying the trim() to a null value is what causes your exception. You should not need this (see Uluk Biy's comment to this answer), but considering you created a user_name TextField, you must check first if the getText() method is not null.
这样的事情应该是技巧：
Something like this should do the trick:
if (user_name.getText() == null || user_name.getText().trim().isEmpty()) {
// your code here
}
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