java - 如何在下次绘图之前清除 jPanel

Question

我在网上搜索过，据说有很多方法可以在开始新绘图之前清除 jPanel，但是，在尝试了所有方法之后，我仍然没有成功 - 结果是面板根本不清除，然后下一个绘图只是与初始绘图重叠，否则我的 paintComponent() 根本不会执行。

Image of problem (Overlapping)

从 GUI 执行绘图的代码:

private void BTCGraphActionPerformed(java.awt.event.ActionEvent evt) {                                         

    Graphics2D gfx = (Graphics2D) jPanel2.getGraphics();
    WebScraper WSBTC = new WebScraper();
    float[] HBTC = WSBTC.HScrapeBTC();

    Graph graphExecute = new Graph();

    graphExecute.CurrentValues(HBTC);
    graphExecute.IndexLarge(HBTC);
    graphExecute.IndexSmall(HBTC);
    graphExecute.Plotter(HBTC);
    graphExecute.paintComponent(gfx);
}                                        

private void LTCGraphActionPerformed(java.awt.event.ActionEvent evt) {                                         

    Graphics2D gfx = (Graphics2D) jPanel2.getGraphics();
    WebScraper WSLTC = new WebScraper();
    float[] HLTC = WSLTC.HScrapeLTC();
    Graph graphExecute = new Graph();

    graphExecute.CurrentValues(HLTC);
    graphExecute.IndexLarge(HLTC);
    graphExecute.IndexSmall(HLTC);
    graphExecute.Plotter(HLTC);
    graphExecute.paintComponent(gfx);
}                                        

private void ETHGraphActionPerformed(java.awt.event.ActionEvent evt) {                                         

    Graphics2D gfx = (Graphics2D) jPanel2.getGraphics();
    WebScraper WSETH = new WebScraper();
    float[] HETH = WSETH.HScrapeETH();
    Graph graphExecute = new Graph();

    graphExecute.CurrentValues(HETH);
    graphExecute.IndexLarge(HETH);
    graphExecute.IndexSmall(HETH);
    graphExecute.Plotter(HETH);
    graphExecute.paintComponent(gfx);
}                                        

paintComponent() 的代码:

protected void paintComponent(Graphics g) {
    super.paintComponent(g);
    Graphics2D g2 = (Graphics2D) g;
    super.paintComponent(g2);
    int DotSize = 10;

    int width = g2.getFontMetrics().stringWidth("Today");
    int middle = width / 2;

    g2.setColor(Color.BLACK);
    /* g2.drawLine(10, 10, 10, 410); //Frame Boundaries
    g2.drawLine(410, 10, 10, 10); //Frame Boundaries
    g2.drawLine(410, 10, 410, 410); //Frame Boundaries
    g2.drawLine(410, 410, 10, 410); //Frame Boundaries */

    //Axis
    g2.drawLine(30, 30, 30, 370);
    g2.drawLine(370, 370, 30, 370);

    //Points & Connections
    PlotPoints(g2, 98, DistanceDay1, DotSize);
    g2.drawLine(98, DistanceDay1, 166, DistanceDay2);
    PlotPoints(g2, 166, DistanceDay2, DotSize);
    g2.drawLine(166, DistanceDay2, 234, DistanceDay3);
    PlotPoints(g2, 234, DistanceDay3, DotSize);
    g2.drawLine(234, DistanceDay3, 302, DistanceDay4);
    PlotPoints(g2, 302, DistanceDay4, DotSize);
    g2.drawLine(302, DistanceDay4, 370, DistanceDay5);
    PlotPoints(g2, 370, DistanceDay5, DotSize);

    //Labels
    g2.drawString("Today", 370 - middle, 390);
    /*  g2.drawString("Test", 98 - middle, 40);
    g2.drawString("Test", 146, 25); */

}

我应该调用什么方法以及我必须将其放置在哪里，以便每次按下按钮绘制新图形时，它都会在绘制之前清除面板

Answer 1

I've searched up online and there are supposedly many ways to clear a jPanel before starting a new drawing however

是的，不要做你正在做的事情。永远不需要手动调用 paintComponent ，并且永远不应该调用 getGraphics ，除了能够返回 null 之外，这不是自定义的方式应该进行绘画。

绘制应该只绘制组件的当前状态。因此，如果您想“清除”面板，请清除它用来决定绘制内容和绘制方式的状态。

您可以通过在要更新的组件上调用 repaint 来触发执行新绘制 channel 的请求。作为绘制过程的一部分，组件的Graphics上下文将被“准备”，通常是通过在其上绘制组件的背景颜色。

首先查看 Performing Custom Painting和 Painting in AWT and Swing

已更新...

一个可运行的示例将使这变得更容易。让我们从...开始...

private void LTCGraphActionPerformed(java.awt.event.ActionEvent evt) {                                         

    Graphics2D gfx = (Graphics2D) jPanel2.getGraphics();
    WebScraper WSLTC = new WebScraper();
    float[] HLTC = WSLTC.HScrapeLTC();
    Graph graphExecute = new Graph();

    graphExecute.CurrentValues(HLTC);
    graphExecute.IndexLarge(HLTC);
    graphExecute.IndexSmall(HLTC);
    graphExecute.Plotter(HLTC);
    graphExecute.paintComponent(gfx);
}    

Graphics2D gfx = (Graphics2D) jPanel2.getGraphics(); 是一个坏主意。 getGraphics 可以返回 null 并且仅提供组件的快照。在下一个绘制周期，它将被更新。

graphExecute.paintComponent(gfx); 是一个坏主意，没有任何理由你应该直接调用任何 paint 方法。绘制系统会告诉您何时需要绘制组件以及要使用的上下文。

然后...

Graph graphExecute = new Graph();

graphExecute.CurrentValues(HLTC);
graphExecute.IndexLarge(HLTC);
graphExecute.IndexSmall(HLTC);
graphExecute.Plotter(HLTC);
graphExecute.paintComponent(gfx);

...等等，什么!？您创建，我假设是一个组件Graph，您为其添加一些信息，然后手动绘制它......

好吧，假设它是某种 JComponent，为什么不将其添加到当前 UI

jPanel2.removeAll();
jPanel2.add(graphExecute);
jPanel2.invalidate();
jPanel2.repaint();

如果Graph不是某种JComponent，那么我们就会遇到一个更大的问题，因为您需要将它传递给可以绘制它的东西。 .也许类似...

public class RenderPane extends JPanel {
    
    private Graph graph;
    
    public RenderPane() {
    }

    public void setGraph(Graph graph) {
        this.graph = graph;
        repaint();
    }

    public Graph getGraph() {
        return graph;
    }
    
    @Override
    public Dimension getPreferredSize() {
        return new Dimension(200, 200);
    }
    
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        Graph grap = getGraph();
        if (grap != null) {
            grap.paintComponent(g);
        }
    }
    
}

那么你也许可以做一些类似的事情......

private void LTCGraphActionPerformed(java.awt.event.ActionEvent evt) {                                         

    jPanel2.removeAll();
    WebScraper WSLTC = new WebScraper();
    float[] HLTC = WSLTC.HScrapeLTC();
    Graph graphExecute = new Graph();

    graphExecute.CurrentValues(HLTC);
    graphExecute.IndexLarge(HLTC);
    graphExecute.IndexSmall(HLTC);
    graphExecute.Plotter(HLTC);

    RenderPane renderer = new RenderPane();
    renderer.setGraph(graphExecute.Plotter);
    jPanel.add(renderer);
}