[英]why picture doesn't show up in swing in java?
我想在中心的邊框布局面板中顯示圖像。 我創建如下圖像面板,然后將其添加到Border-layout的中心。 我不知道為什么圖像沒有顯示,也沒有錯誤。 可能是什么原因,我該如何解決?
public class ImagePanel extends WebPanel {
private Image image;
private Image scaledImage;
private int imageWidth = 0;
private int imageHeight = 0;
//constructor
public ImagePanel() {
super();
}
public void loadImage(String file) throws IOException {
File filetest= new File("C:\\tmp\\axiuser\\Pictures\\CLA0014.png");
image = ImageIO.read(filetest);//new File(file)
imageWidth = image.getWidth(this);
imageHeight = image.getHeight(this);
setScaledImage();
}
//e.g., containing frame might call this from formComponentResized
public void scaleImage() {
setScaledImage();
}
//override paintComponent
public void paintComponent(Graphics g) {
super.paintComponent(g);
if ( scaledImage != null ) {
//System.out.println("ImagePanel paintComponent " + ++paintCount);
g.drawImage(scaledImage, 0, 0, this);
}
}
private void setScaledImage() {
if ( image != null ) {
//use floats so division below won't round
float iw = imageWidth;
float ih = imageHeight;
float pw = this.getWidth(); //panel width
float ph = this.getHeight(); //panel height
if ( pw < iw || ph < ih ) {
if ( (pw / ph) > (iw / ih) ) {
iw = -1;
ih = ph;
} else {
iw = pw;
ih = -1;
}
//prevent errors if panel is 0 wide or high
if (iw == 0) {
iw = -1;
}
if (ih == 0) {
ih = -1;
}
scaledImage = image.getScaledInstance(
new Float(iw).intValue(), new Float(ih).intValue(), Image.SCALE_DEFAULT);
} else {
scaledImage = image;
}
}
}
}
你從不打電話給你的方法
public void loadImage (String file)
SSCCE:
import java.awt.*;
import javax.swing.*;
import java.awt.event.*;
import java.io.*;
import javax.imageio.*;
public class ImagePanel extends JPanel {
private Image image;
private Image scaledImage;
public void loadImage (String filename) throws IOException {
image = ImageIO.read (new File (filename));
setScaledImage ();
}
public void paintComponent (Graphics g) {
super.paintComponent (g);
if ( scaledImage != null) {
// System.out.println ("ImagePanel paintComponent ");
g.drawImage (scaledImage, 0, 0, this);
}
}
private void setScaledImage () {
if (image != null) {
//use floats so division below won't round
int imageWidth = image.getWidth (this);
int imageHeight = image.getHeight (this);
float iw = imageWidth;
float ih = imageHeight;
float pw = this.getWidth (); //panel width
float ph = this.getHeight (); //panel height
if ( pw < iw || ph < ih) {
if ( (pw / ph) > (iw / ih)) {
iw = -1;
ih = ph;
} else {
iw = pw;
ih = -1;
}
//prevent errors if panel is 0 wide or high
if (iw == 0) {
iw = -1;
}
if (ih == 0) {
ih = -1;
}
scaledImage = image.getScaledInstance (
new Float (iw).intValue (), new Float (ih).intValue (), Image.SCALE_DEFAULT);
} else {
scaledImage = image;
}
}
}
public static void main (String [] args) throws IOException {
ImagePanel ip = new ImagePanel ();
ip.loadImage ("./sample.png");
JFrame jf = new JFrame ();
jf.setLayout (new BorderLayout ());
jf.add (ip, BorderLayout.CENTER);
jf.setSize (400, 400);
jf.setLocation (150, 150);
jf.setVisible (true);
jf.setDefaultCloseOperation (JFrame.EXIT_ON_CLOSE);
}
}
縮放不起作用,但在這里你有一些東西要開始。 (注意我重命名了圖像)。
只需覆蓋JPanel
getPreferredSize()
,就像使用paintComponent(...)
方法一樣。 讓它返回一些Dimension
對象,如:
public Dimension getPreferredSize()
{
return (new Dimension(300, 300));
}
這將允許您查看圖像。
也許沒有為*.png
定義的Reader。您可以使用ImageIO.getReaderFormatNames()
查看可用的圖像閱讀器列表
我認為你應該將面板設置為不透明:
setOpaque(false)
在不知道程序何時實際調用paintComponent()
的情況下,我們無法分辨。 但是如果在已經顯示GUI( setVisible
) 之后調用loadImage
方法,則需要在面板上調用repaint()
或invalidate()
以觸發組件的重繪(並以這種方式更新GUI)。
考慮使用JLabel
來顯示圖像。
JLabel myLabel=new JLabel();
myLabel.setIcon(new ImageIcon("C:\\tmp\\axiuser\\Pictures\\CLA0014.png"));
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