Java:ImageIcon - 图像文件更新，但 Java 框架中的图像图标没有

Java: ImageIcon - image file updating but image icon in Java frame not(Java:ImageIcon - 图像文件更新，但 Java 框架中的图像图标没有)

问题描述

I have got a ImageIcon in a Jlabel in a JFrame (Java GUI).

The ImageIcon should get updated based on pressing a Calculate button (i.e. calcButton.addActionListener(new ActionListener() ) with part of the code in the method:

icon2 = new ImageIcon("M:\Repos\rtrans\radTransPlot.png");
Plot1.setIcon(icon2);
frame.add(Plot1,gc);
frame.setVisible(true);

The initial ImageIcon (icon1) is blank:

public class RadTransGui 
{
private ImageIcon icon1 = new ImageIcon("M:\Repos\rtrans\radTransPlotEmpty.png");
private ImageIcon icon2;
private JLabel Plot1 = new JLabel(icon1);

and gets properly updated based on the first Calculate button press but not after subsequent presses of Calculate button. The contents of M:Repos trans adTransPlot.png gets updated correctly each time Calculate is pressed.

I have tried setting the ImageIcon to null and adding and removing the JLabel to the frame each time the Calculate button is pressed.

Any ideas? Thanks.

The constructor of ImageIcon() internally uses Toolkit.getDefaultToolkit().getImage.

You have to manually use Toolkit.getDefaultToolkit().createImage instead of Toolkit.getDefaultToolkit().getImage. The latter uses cache whereas the former doesn't and always returns a new instance.

new ImageIcon(Toolkit.getDefaultToolkit().createImage("..filename.."))

From the javadoc of createImage:

The returned Image is a new object which will not be shared with any other caller of this method or its getImage variant.

Compare with the javadoc of getImage:

The underlying toolkit attempts to resolve multiple requests with the same filename to the same returned Image. [...] If the image data contained in the specified file changes, the Image object returned from this method may still contain stale information which was loaded from the file after a prior call.

There seems to be no javadoc or spec that prescribes that ImageIcon should use cached images, so it's a perfect example of how fragile programming is if you don't know 100% what you're doing. Even if it works in one environment doesn't guarantee it always works.

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