我有一个按钮，该按钮将从字段中获取我的用户名和密码，并向后端发送请求以进行身份验证。我正在使用线程，因此按钮的动画和场景不会像这样冻结：
Service<Void> service = new Service<Void>() {
@Override
protected Task<Void> createTask() {
return new Task<Void>() {
@Override
protected Void call() throws Exception {
//do authentication
if(responseStatus != 200){
authenticated = false
}else{
authenticate = true
}
Platform.runLater(() -> {
try{
if(authenticated) {
changeScene();
}
}finally{
latch.countDown();
}
});
latch.await();
return null;
}
};
}
};
service.start();
private void changeScene(){
try {
Stage window = (Stage)loginPane.getScene().getWindow();
LoggedFirstStyle.displayLoggedScene();
window.close();
} catch (IOException e) {
e.printStackTrace();
}
}
但是事情是，如果我多次单击按钮，稍后运行的平台将执行几次，因此changeScene也会打开几个场景。我这样做的方法是否正确，如果可以，如何防止以同一方法打开多个线程？
答案 0 :(得分：2)
Service提供了“重用” Task的功能。我将“重用”用引号引起来，因为实际上发生的是Service每次启动时都会创建一个新的Task。有关Service和Task之间的区别和用法的详细信息，您可以：
Service和Task的文档，也许还有Worker。由于Service被重用，因此您只应创建一个实例。它还保持状态，因此只能“一次”执行。换句话说，同一Service不能并行执行多次。 Service完成后，它将处于SUCCEEDED，CANCELLED或FAILED状态；要再次启动Service，您必须调用restart()（将取消正在运行的Service）或调用reset()，然后再次调用start()。
在Service运行时，您希望禁用某些UI组件，以便用户无法尝试多次启动它。您可以通过侦听器和/或绑定来实现。如果需要，您还可以进行检查，以使您的代码不会尝试启动Service（如果已在运行）。是否需要进行这些检查取决于可以启动Service的代码及其执行方式。
这是一个小例子。它使用FXML创建接口，但重要的部分是LoginController和LoginService类。根据您的应用程序，您可能还想添加一种取消登录的方法。
Main.java
package com.example;
import java.io.IOException;
import javafx.application.Application;
import javafx.fxml.FXMLLoader;
import javafx.scene.Parent;
import javafx.scene.Scene;
import javafx.stage.Stage;
public class Main extends Application {
@Override
public void start(Stage primaryStage) throws IOException {
// Login.fxml is in the same package as this class
Parent root = FXMLLoader.load(getClass().getResource("Login.fxml"));
primaryStage.setScene(new Scene(root));
primaryStage.setTitle("Service Example");
primaryStage.show();
}
}
LoginService.java
package com.example;
import javafx.beans.property.SimpleStringProperty;
import javafx.beans.property.StringProperty;
import javafx.concurrent.Service;
import javafx.concurrent.Task;
public class LoginService extends Service<Boolean> {
private final StringProperty username = new SimpleStringProperty(this, "username");
public final void setUsername(String username) { this.username.set(username); }
public final String getUsername() { return username.get(); }
public final StringProperty usernameProperty() { return username; }
private final StringProperty password = new SimpleStringProperty(this, "password");
public final void setPassword(String password) { this.password.set(password); }
public final String getPassword() { return password.get(); }
public final StringProperty passwordProperty() { return password; }
@Override
protected Task<Boolean> createTask() {
return new LoginTask(getUsername(), getPassword());
}
private static class LoginTask extends Task<Boolean> {
private final String username;
private final String password;
public LoginTask(String username, String password) {
this.username = username;
this.password = password;
}
@Override
protected Boolean call() throws Exception {
Thread.sleep(3_000L); // simulate long running work...
return !isCancelled() && "root".equals(username) && "root".equals(password);
}
}
}
LoginController.java
package com.example;
import javafx.beans.binding.Bindings;
import javafx.beans.binding.BooleanBinding;
import javafx.concurrent.Worker;
import javafx.event.ActionEvent;
import javafx.fxml.FXML;
import javafx.scene.Cursor;
import javafx.scene.control.Alert;
import javafx.scene.control.Button;
import javafx.scene.control.PasswordField;
import javafx.scene.control.TextField;
import javafx.scene.layout.GridPane;
public class LoginController {
@FXML private GridPane root;
@FXML private TextField userField;
@FXML private PasswordField passField;
@FXML private Button loginBtn;
private LoginService service;
@FXML
private void initialize() {
service = new LoginService();
service.usernameProperty().bind(userField.textProperty());
service.passwordProperty().bind(passField.textProperty());
// Don't let user interact with UI while trying to login
BooleanBinding notReadyBinding = service.stateProperty().isNotEqualTo(Worker.State.READY);
userField.disableProperty().bind(notReadyBinding);
passField.disableProperty().bind(notReadyBinding);
loginBtn.disableProperty().bind(notReadyBinding);
root.cursorProperty().bind(
Bindings.when(service.runningProperty())
.then(Cursor.WAIT)
.otherwise(Cursor.DEFAULT)
);
service.setOnSucceeded(event -> serviceSucceeded());
service.setOnFailed(event -> serviceFailed());
}
private void serviceSucceeded() {
if (service.getValue()) {
/*
* Normally you'd change the UI here to show whatever the user needed to
* sign in to see. However, to allow experimentation with this example
* project we simply show an Alert and call reset() on the LoginService.
*/
showAlert(Alert.AlertType.INFORMATION, "Login Successful", "You've successfully logged in.");
service.reset();
} else {
showAlert(Alert.AlertType.ERROR, "Login Failed", "Your username or password is incorrect.");
service.reset();
}
}
private void serviceFailed() {
showAlert(Alert.AlertType.ERROR, "Login Failed", "Something when wrong while trying to log in.");
service.getException().printStackTrace();
service.reset();
}
private void showAlert(Alert.AlertType type, String header, String content) {
Alert alert = new Alert(type);
alert.initOwner(root.getScene().getWindow());
alert.setHeaderText(header);
alert.setContentText(content);
alert.showAndWait();
}
@FXML
private void handleLogin(ActionEvent event) {
event.consume();
// isBlank() is a String method added in Java 11
boolean blankUsername = userField.textProperty().getValueSafe().isBlank();
boolean blankPassword = passField.textProperty().getValueSafe().isBlank();
if (blankUsername || blankPassword) {
showAlert(Alert.AlertType.ERROR, null, "Both username and password must be specified.");
} else {
service.start();
}
}
}
Login.fxml
<?xml version="1.0" encoding="UTF-8"?>
<?import javafx.geometry.Insets?>
<?import javafx.scene.control.Button?>
<?import javafx.scene.control.Label?>
<?import javafx.scene.control.PasswordField?>
<?import javafx.scene.control.TextField?>
<?import javafx.scene.layout.ColumnConstraints?>
<?import javafx.scene.layout.GridPane?>
<?import javafx.scene.layout.RowConstraints?>
<?import javafx.scene.text.Font?>
<GridPane fx:id="root" maxHeight="-Infinity" maxWidth="-Infinity" minHeight="-Infinity" minWidth="-Infinity" vgap="20.0"
xmlns:fx="http://javafx.com/fxml/1" xmlns="http://javafx.com/javafx/10.0.1"
fx:controller="com.example.LoginController">
<columnConstraints>
<ColumnConstraints hgrow="SOMETIMES" minWidth="-Infinity" percentWidth="50.0"/>
<ColumnConstraints halignment="RIGHT" hgrow="SOMETIMES" minWidth="-Infinity" percentWidth="50.0"/>
</columnConstraints>
<rowConstraints>
<RowConstraints minHeight="-Infinity" percentHeight="25.0" vgrow="SOMETIMES"/>
<RowConstraints minHeight="-Infinity" percentHeight="25.0" vgrow="SOMETIMES"/>
<RowConstraints minHeight="-Infinity" percentHeight="25.0" vgrow="SOMETIMES"/>
<RowConstraints minHeight="-Infinity" percentHeight="25.0" vgrow="SOMETIMES"/>
</rowConstraints>
<children>
<Button fx:id="loginBtn" defaultButton="true" mnemonicParsing="false" onAction="#handleLogin" text="Login"
GridPane.columnIndex="1" GridPane.rowIndex="3"/>
<Label minWidth="-Infinity" text="Welcome">
<font>
<Font name="Segoe UI" size="32.0"/>
</font>
</Label>
<TextField fx:id="userField" prefColumnCount="20" promptText="Username" GridPane.columnSpan="2"
GridPane.rowIndex="1"/>
<PasswordField fx:id="passField" prefColumnCount="20" promptText="Password" GridPane.columnSpan="2"
GridPane.rowIndex="2"/>
</children>
<padding>
<Insets bottom="50.0" left="50.0" right="50.0" top="50.0"/>
</padding>
</GridPane>