如何计算JavaFX中String的像素宽度？ [英] How to calculate the pixel width of a String in JavaFX?

问题描述

似乎没有API调用来计算Java FX 2.2中文本字符串的宽度（以像素为单位）。在其他论坛上已经提出了变通方法的建议，但是我使用默认字体或其他方式创建或查找返回String宽度的任何代码的尝试都失败了。任何帮助将不胜感激。

It appears that there is no API call to calculate the width (in pixels) of a text string in Java FX 2.2. There have been suggestions of workarounds on other forums, but my efforts to create or find any code that returns the width of a String, either using the default font or otherwise, have failed. Any help would be appreciated.

推荐答案

如果您只是测量没有CSS的默认字体：

If you are just measuring the default font without CSS:

1. 将要测量的字符串放在Text对象中。


2. 获取Text对象布局边界的宽度。

如果您需要申请CSS：

If you need to apply CSS:

1. 放置要在Text对象中测量的字符串。


2. 创建一次性场景并将Text对象放置在场景中。


3. 拍摄文本的快照（如果您使用的是Java 7）或者调用 applyCss for Java 8。


4. 获取Text对象布局边界的宽度。

1. Place the String to be measured in a Text object.
2. Create a throwaway Scene and place the Text object in the Scene.
3. Take a snapshot of the Text (if you are using Java 7) or call applyCss for Java 8.
4. Get the width of the Text object's layout bounds.

这是有效的，因为它强制在Text上进行布局传递，计算它的布局边界。
步骤2中的场景是必需的，因为这只是CSS处理器的工作方式（它需要一个节点位于一个场景中才能完成它的工作）。如果您想进一步了解处理，请务必阅读applyCss的链接javadoc。

This works because it forces a layout pass on the Text which calculates it's layout bounds. The scene in step 2 is required because that is just the way the CSS processor works (it needs a node to be located in a Scene to be able to do its job). Definitely read the linked javadoc for applyCss if you want to understand the processing further.

示例代码

import javafx.application.Application;
import javafx.scene.Scene;
import javafx.scene.control.*;
import javafx.scene.text.Text;
import javafx.stage.Stage;

// displays the width in pixels of an arbitrary piece of text.
public class MeasureText extends Application {
  public static void main(String[] args) { launch(args); }
  @Override public void start(Stage stage) throws Exception {
    final Text text = new Text("XYZZY");
    new Scene(new Group(text));

    // java 7 => 
    //    text.snapshot(null, null);
    // java 8 =>
    text.applyCss(); 

    final double width = text.getLayoutBounds().getWidth();

    stage.setScene(new Scene(new Label(Double.toString(width))));
    stage.show();
  }
}

示例程序输出（显示以像素为单位的宽度）任意一段文字）：

Sample program output (displays the width in pixels of an arbitrary piece of text):

如果将文本打印到带有设置字体的graphicscontext，这会如何改变（如果有的话）？

How (if at all) would this change if the text was printed to a graphicscontext with a set font?

将字体应用于包含您将绘制到画布的相同消息的文本对象。与测量绘制到场景图形的文本不同，绘制到画布的项目没有应用CSS，因此您无需将Text对象放置在场景中，并在测量文本之前将CSS应用于该场景。您可以测量文本对象的布局边界，它将与使用相同字体在画布中绘制的文本边界相同。

Apply the font to a text object containing the same message you will plot to the canvas. Unlike when you are measuring text plotted to the scene graph, items plotted to a canvas do not have CSS applied to them, so you don't need to place the Text object in a scene and have CSS applied to it before measuring the text. You can measure the layout bounds of your text object and it will be the same as the bounds of the text plotted within the canvas with the same font.

import javafx.application.Application;
import javafx.scene.Scene;
import javafx.scene.canvas.*;
import javafx.scene.control.Label;
import javafx.scene.layout.VBox;
import javafx.scene.text.*;
import javafx.stage.Stage;

// displays the width in pixels of an arbitrary piece of text (which has been plotted on a canvas).
public class MeasureText extends Application {
    @Override
    public void start(Stage stage) throws Exception {
        final String msg = "XYZZY";
        final Text text = new Text(msg);
        Font font = Font.font("Arial", 20);
        text.setFont(font);

        final double width = text.getLayoutBounds().getWidth();

        Canvas canvas = new Canvas(200, 50);
        GraphicsContext gc = canvas.getGraphicsContext2D();
        gc.setFont(font);
        gc.fillText(msg, 0, 40);

        stage.setScene(new Scene(
                new VBox(new Label(Double.toString(width)), canvas))
        );
        stage.show();
    }

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

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