java - Javafx 只启动一个线程,即使按钮被点击多次
问题描述
我有一个按钮,它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。我正在使用一个线程,所以我的按钮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();
}
}
但事情是,如果我多次单击按钮,稍后运行的平台将执行多次,changeScene 也是如此,并且打开了几个场景。我这样做的方式好吗?如果是这样,我怎样才能防止在同一方法中打开多个线程?
解决方案
AService
提供了“重用” a 的能力Task
。我将“重用”放在引号中,因为真正发生的是每次启动时都会Service
创建一个新的。Task
有关两者之间的差异和用法的更多信息,Service
您Task
可以:
- 阅读
Service
and的文档Task
——也许Worker
也可以。 - 阅读JavaFX 中的并发。
- 请参阅此 Stack Overflow 问题:Task vs Service for database operations。
由于 aService
旨在被重用,您应该只创建一个实例。它还维护状态,因此只能“一次”执行一次。换句话说,Service
不能并行执行多次。当Service
完成时,它将处于SUCCEEDED
、CANCELLED
或FAILED
状态;要再次开始,Service
您必须调用restart()
(将取消正在运行Service
)或在再次调用reset()
之前调用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/或绑定来做到这一点。如果需要,您还可以进行检查,以便您的代码在Service
它已经运行时不会尝试启动。是否需要这些检查取决于可以启动哪些代码Service
以及如何执行它。
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。
主.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();
}
}
登录服务.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);
}
}
}
登录控制器.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();
}
}
}
登录.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>
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