按键绑定到ObservableMap的值 [英] Binding to value of ObservableMap by key

问题描述

JavaFX是否具有绑定类型，其中我提供带有键的可观察映射，并且计算值将始终在键/值对更改时更新？从地图中删除该密钥将导致 null 值，将其重新添加将追溯该值。

<我一直在寻找JavaDoc并找到 MapProperty ， MapBinding 和 ObservableMapValue ，但似乎没有任何东西可以达到这个目的。

我已经设计了我自己的变种，但是想要使用一个相当安全且经过测试的版本。

解决方案

你可以这样做

  someObjectProperty.bind（Bindings.createObjectBinding（
（） - > myObservableMap.get（key），myObservableMap）; 
  

或者，@ VGR在评论中指出

  someObjectProperty.bind（Bindings。 valueAt（someObservableMap，key））; 
  

这是使用第二种方法的SSCCE：

  import java.util.Arrays; 
 
 import javafx.application.Application; 
i mport javafx.beans.binding.Bindings; 
 import javafx.collections.FXCollections; 
 import javafx.collections.ObservableMap; 
 import javafx.event.ActionEvent; 
 import javafx.event.EventHandler; 
 import javafx.geometry.Insets; 
 import javafx.scene.Scene; 
 import javafx.scene.control.Button; 
 import javafx.scene.control.ComboBox; 
 import javafx.scene.control.Label; 
 import javafx.scene.control.TextField; 
 import javafx.scene.layout.GridPane; 
 import javafx.stage.Stage; 
 
公共类BindToObservableMap扩展Application {
 
 private static final String [] keys = {key1，key2，key3}; 
 
 @Override 
 public void start（Stage primaryStage）{
 ObservableMap< String，String> map = FXCollections.observableHashMap（）; 
 for（String k：keys）map.put（k，k.replaceAll（key，value））; 
 
 GridPane grid = new GridPane（）; 
 grid.setHgap（5）; 
 grid.setVgap（5）; 
 grid.setPadding（new Insets（10））; 
 for（int i = 0; i< keys.length; i ++）{
 grid.add（new Label（keys [i]），0，i）; 
 Label boundLabel = new Label（）; 
 boundLabel.textProperty（）。bind（Bindings.valueAt（map，keys [i]））; 
 grid.add（boundLabel，1，i）; 
} 
 
 ComboBox< String> keyCombo = new ComboBox<>（）; 
 keyCombo.getItems（）。setAll（keys）; 
 TextField valueField = new TextField（）; 
按钮更新=新按钮（更新）; 
 EventHandler< ActionEvent> handler = e  - > {
 map.put（keyCombo.getValue（），valueField.getText（））; 
 valueField.clear（）; 
 keyCombo.requestFocus（）; 
}; 
 valueField.setOnAction（handler）; 
 update.setOnAction（handler）; 
 
 grid.addRow（keys.length，keyCombo，valueField）; 
 grid.add（update，0，keys.length + 1）; 
 
场景场景=新场景（网格）; 
 primaryStage.setScene（scene）; 
 primaryStage.show（）; 
} 
 
 public static void main（String [] args）{
 launch（args）; 
} 
} 
  

Does JavaFX have a binding type where i supply an observable map with a key and the computed value will always update as the key/value pair changes? Removing that key the key from the map will result to a null value, adding it back will track that value back.

I've been looking around the JavaDoc and found MapProperty, MapBinding and ObservableMapValue, but nothing seems to serve this purpose.

I've already designed my own variant, but would like to use a rather failsafe and tested version.

解决方案

You can just do

someObjectProperty.bind(Bindings.createObjectBinding(
    () -> myObservableMap.get(key), myObservableMap);

or, as @VGR points out in the comments

someObjectProperty.bind(Bindings.valueAt(someObservableMap, key));

Here is a SSCCE using the second approach:

import java.util.Arrays;

import javafx.application.Application;
import javafx.beans.binding.Bindings;
import javafx.collections.FXCollections;
import javafx.collections.ObservableMap;
import javafx.event.ActionEvent;
import javafx.event.EventHandler;
import javafx.geometry.Insets;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.control.ComboBox;
import javafx.scene.control.Label;
import javafx.scene.control.TextField;
import javafx.scene.layout.GridPane;
import javafx.stage.Stage;

public class BindToObservableMap extends Application {

    private static final String[] keys = {"key1", "key2", "key3"};

    @Override
    public void start(Stage primaryStage) {
        ObservableMap<String, String> map = FXCollections.observableHashMap();
        for (String k : keys) map.put(k, k.replaceAll("key", "value"));

        GridPane grid = new GridPane();
        grid.setHgap(5);
        grid.setVgap(5);
        grid.setPadding(new Insets(10));
        for (int i = 0 ; i < keys.length; i++) {
            grid.add(new Label(keys[i]), 0, i);
            Label boundLabel = new Label();
            boundLabel.textProperty().bind(Bindings.valueAt(map, keys[i]));
            grid.add(boundLabel, 1, i);
        }

        ComboBox<String> keyCombo = new ComboBox<>();
        keyCombo.getItems().setAll(keys);
        TextField valueField = new TextField();
        Button update = new Button("Update");
        EventHandler<ActionEvent> handler = e -> {
            map.put(keyCombo.getValue(), valueField.getText());
            valueField.clear();
            keyCombo.requestFocus();
        };
        valueField.setOnAction(handler);
        update.setOnAction(handler);

        grid.addRow(keys.length, keyCombo, valueField);
        grid.add(update, 0, keys.length + 1);

        Scene scene = new Scene(grid);
        primaryStage.setScene(scene);
        primaryStage.show();
    }

    public static void main(String[] args) {
        launch(args);
    }
}

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