如何检查文本字段是否为空？

Question

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。这些是文本字段：

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");

现在我只想测试一个文本字段的验证。这是我链接到 createBtn:

的验证函数

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();
    }
}

但是我在按下 'Create Account' 按钮时收到此错误消息：

Exception in thread "JavaFX Application Thread" 

java.lang.NullPointerException
    at opdracht1.Opdracht1.validation(Opdracht1.java:36)
    at opdracht1.Opdracht1.handle(Opdracht1.java:103)
    at opdracht1.Opdracht1.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.handle(BehaviorSkinBase.java:96)
    at com.sun.javafx.scene.control.skin.BehaviorSkinBase.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$MouseHandler.access00(Scene.java:3485)
    at javafx.scene.Scene.impl_processMouseEvent(Scene.java:1762)
    at javafx.scene.Scene$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$handleMouseEvent5(GlassViewEventHandler.java:388)
    at com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(QuantumToolkit.java:389)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:387)
    at com.sun.glass.ui.View.handleMouseEvent(View.java:555)
    at com.sun.glass.ui.View.notifyMouse(View.java:937)
    at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
    at com.sun.glass.ui.win.WinApplication.lambda$null9(WinApplication.java:191)
    at java.lang.Thread.run(Thread.java:745)

提前致谢！

Answer 1

首先，检查user_name是否不是null。如果不是，则说明您在代码中的某处为 JavaFX 组件设置了 null 文本值。

if(user_name.getText().trim().isEmpty()){

在任何情况下，将 trim() 应用于 null 值是导致异常的原因。你不应该需要这个（参见 Uluk Biy 对这个答案的评论），但考虑到你创建了一个 user_name TextField，你必须首先检查 getText()方法不是 null.

像这样应该可以解决问题：

if (user_name.getText() == null || user_name.getText().trim().isEmpty()) {
     // your code here
}

Answer 2

这可以通过

简单地检查

if(textField.getText().trim().equals(""))
{
system.out.println("textField is empty");
}

Answer 3

您可以测试此代码用您的 TextFeild 的名称替换我的冠军的名称

if ((nom_pt.getText().toString().compareTo("") == 0) ||
    (prenom_pt.getText().toString().compareTo("") == 0) ||
    (cin_pt.getText().toString().compareTo("") == 0) ||
    (gsm_pt.getText().toString().compareTo("") == 0)) {

    JOptionPane.showMessageDialog(null, "champs vide");

} else {  JOptionPane.showMessageDialog(null, "Enregistrement a été  ajouter");  }

Answer 4

您可以使用Button disableProperty 来绑定TextField。当文本字段为空时，按钮将被禁用，否则将被启用。

使用下面提到的代码

createBtn.disableProperty().bind(
    Bindings.createBooleanBinding( () -> 
        user_name.getText().trim().isEmpty(), user_name.textProperty()
    )
    // If you want to check more text field, use it as by removing comments
    //.or(  Bindings.createBooleanBinding(
    //         first_name.getText.trim().isEmpty(), first_name.textProperty()
    //     )
    //  )

);

Answer 5

好的，我就是这样做的，而且很有效。

如果上述 none 有效，请尝试以下操作：

创建一个字符串变量，比方说String username；接下来，尝试以下操作：

if(username.trim().isEmpty())

最初的建议对我没有用，但创建字符串对我有用，所以如果以上建议对您不起作用，请试一试。

Answer 6

textField.getText().trim().equals("")

以上陈述对我来说就像一个魅力。

如何检查文本字段是否为空？

How to check if textfield is empty?

javafx

textfield