java 从另一个 Applet 启动另一个 Applet

Launching another Applet from another Applet

提问by Snehasish

I have made a Loader Applet which greets the user and when user clicks the button displayed on that Applet it then launches the main applet and the Loader Applet is destroyed.

我制作了一个加载程序小程序来迎接用户，当用户单击该小程序上显示的按钮时，它会启动主小程序，加载程序小程序将被销毁。

But on clicking Another applet is not launched !

但是点击另一个小程序不会启动！

Loader Applet:

加载程序小程序：

import java.awt.Button;
import java.awt.FlowLayout;
import java.awt.Graphics;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JApplet;

public class Loader extends JApplet implements ActionListener{
    Display secondApplet;
    Button button;

    @Override
    public void init() {
        setSize(800,600);
    }

    @Override
    public void start() {
        setLayout(new FlowLayout());
        button = new Button ("Click me !!");
        add(button);
        button.addActionListener(this);
    }

    @Override
    public void paint(Graphics g) {

    }

    @Override
    public void actionPerformed(ActionEvent e) {
        secondApplet = (Display)getAppletContext().getApplet("Display");
        if (secondApplet != null) {
            secondApplet.init();
            secondApplet.start();
        }
        else {
            System.out.println("Not Running\n");
        }
    }
}

Display Applet:

显示小程序：

import java.awt.Color;
import java.awt.Graphics;
import javax.swing.JApplet;

public class Display extends JApplet {

    @Override
    public void init() {
        setSize(600,400);
    }

    @Override
    public void paint(Graphics g) {
        g.fillRect(0, 0, this.getWidth(), this.getHeight());
    }
}

How can I create an instance of the other Applet and destroy the current Applet !!

如何创建另一个 Applet 的实例并销毁当前 Applet ！！

回答by emecas

Since an Applet/JApple is a java.awt.Panelitself, then you can embed one into the other, for your specific case you can embed Displayinto Loaderusing a Panel in Loaderto reload Displayas you need.

由于一个Applet / JApple是java.awt.Panel本身，那么你可以嵌入到彼此，为您的特定情况下，你可以嵌入显示到装载机在使用面板加载到重装显示，因为你需要。

Something like this:

像这样的东西：

Panel container = new Panel();
container.setLayout(new GridLayout(1,0));
container.add(secondApplet); //Display Applet
add(container):

secondApplet.init();
secondApplet.start();

button.setVisible(false);

回答by Andrew Thompson

There are so many things wrong with the applets it is hard to know where to begin. But let us concentrate 1st on a more sensible strategy to cause the change beteween one view and another.

小程序有很多问题，很难知道从哪里开始。但是，让我们首先关注一个更明智的策略，以引起一种观点和另一种观点之间的变化。

1. Instead of having two applets, have two panels that are swapped in a CardLayout
2. Instead of having both applets in one page, call getAppletContext().showDocument(secondAppletURL);. Presumably secondAppletURLis different to the URL of the page that hosts the first applet.

1. 不是有两个小程序，而是有两个面板，它们在一个 CardLayout
2. 不要将两个小程序放在一页中，而是调用getAppletContext().showDocument(secondAppletURL);. 大概secondAppletURL与承载第一个小程序的页面的 URL 不同。

OK - the problems with the first applet:

好的 - 第一个小程序的问题：

1. Don't try to set the size of an applet. It is set by the HTML.
2. All the methods calls in the start()method should be moved to the init()method, since the start()method might be called repeatedly. Then there is no reason to override start()at all.
3. Don't mix Swing (e.g. JApplet) & AWT (e.g. Button) components without good cause. In this case, use JButtoninstead of Button.
4. As a stylistic point, it is typically better to create an anonymous inner ActionListenerthan implement it on the parent class.
5. Overriding paint()with an empty implementation is not a good idea. The original paint()draws the applet and components, so now it would do nothing.
6. The methods in the actionPerformed()are equally nonsensical. An applet does not get included into the AppletContextuntil after init()& start()have been called, which would mean that calling those methods explicitly causes them to be invoked a second time. While the start()method is meant to be called multiple times, the init()method should only be called once.

1. 不要试图设置小程序的大小。它由 HTML 设置。
2. 方法中的所有方法调用start()都应该移动到init()方法中，因为start()方法可能会被重复调用。那么根本没有理由覆盖start()。
3. 不要在没有JApplet正当Button理由的情况下混合 Swing（例如）和 AWT（例如）组件。在这种情况下，请使用JButton代替Button。
4. 作为一个风格点，创建匿名内部通常ActionListener比在父类上实现它更好。
5. paint()用空实现覆盖不是一个好主意。原来是paint()绘制小程序和组件，所以现在什么都不做。
6. 中的方法actionPerformed()同样荒谬。小程序不会被包含到调用AppletContext之后，直到init()&start()被调用，这意味着显式调用这些方法会导致它们被第二次调用。虽然该start()方法旨在被多次调用，但该init()方法只能被调用一次。

2nd Applet.

第二个小程序。

1. Ditto point 1. re the 1st applet.
2. The overridden paint()method ..would paint the BG color (or the FG color - not sure) but nothing else. Again, don't override it.

1. 同上点 1. 是第一个小程序。
2. 覆盖的paint()方法..将绘制 BG 颜色（或 FG 颜色 - 不确定），但不会绘制其他颜色。再次，不要覆盖它。

回答by SudoRahul

Try this method to load another applet. See if it works.

试试这个方法来加载另一个小程序。看看它是否有效。

Class applet2 = Class.forName("Applet2");
Applet appletToLoad = (Applet)applet2.newInstance();
appletToLoad.setStub(this);
setLayout(new GridLayout(1,0));
add(appletToLoad);
appletToLoad.init();
appletToLoad.start();