Initial commit

resources/META-INF/plugin.xml

+<idea-plugin>
+    <!-- 插件相关信息， 会展示在IDEA插件的描述中 -->
+    <!-- 插件唯一id, 遵循使用包名的原则 -->
+    <id>com.duanledexianxianxian.plugin.sample</id>
+    <!-- 插件名称 -->
+    <name>sample</name>
+    <!-- 插件版本 -->
+    <version>1.0</version>
+    <!-- 开发者信息 -->
+    <vendor email="fengyuchenglun@foxmail.com" url="https://github.com/fengyuchenglun">fengyuchenglun</vendor>
+    <!-- 插件的描述 -->
+    <description>
+        This is IDEA plugin. Just for test and study.
+    </description>
+    <!-- 插件版本变更信息 -->
+    <change-notes>
+        This is IDEA plugin. Just for test and study.
+    </change-notes>
+
+    <!-- please see http://www.jetbrains.org/intellij/sdk/docs/basics/getting_started/build_number_ranges.html for description -->
+    <!-- 插件兼容IDEA的最大和最小build号，不配置则不做限制 -->
+    <idea-version since-build="173.0"/>
+
+    <!-- please see http://www.jetbrains.org/intellij/sdk/docs/basics/getting_started/plugin_compatibility.html
+         on how to target different products -->
+    <!-- uncomment to enable plugin in all products
+    <depends>com.intellij.modules.lang</depends>
+    -->
+    <depends>com.intellij.modules.platform</depends>
+
+
+    <!-- 声明该插件对IDEA core或其他插件的扩展 -->
+    <extensions defaultExtensionNs="com.intellij">
+        <!-- Add your extensions here -->
+        <applicationService serviceInterface="com.duanledexianxianxian.plugin.service.application.SampleApplication"
+                            serviceImplementation="com.duanledexianxianxian.plugin.service.application.impl.SampleApplicationImpl"/>
+        <applicationService serviceInterface="com.duanledexianxianxian.plugin.service.application.MyCounter"
+                            serviceImplementation="com.duanledexianxianxian.plugin.service.application.impl.MyCounterImpl"/>
+    </extensions>
+    <!-- Actions: 如添加一个文件右击菜单按钮 -->
+    <actions>
+        <!-- Add your actions here -->
+    </actions>
+
+    <project-components>
+        <component>
+            <implementation-class>com.duanledexianxianxian.plugin.component.project.MaxProject</implementation-class>
+        </component>
+    </project-components>
+
+</idea-plugin>
\ No newline at end of file

src/com/duanledexianxianxian/plugin/component/project/MaxProject.java

+package com.duanledexianxianxian.plugin.component.project;
+
+import com.duanledexianxianxian.plugin.constant.AppConstants;
+import com.duanledexianxianxian.plugin.service.application.MyCounter;
+import com.intellij.openapi.components.ProjectComponent;
+import com.intellij.openapi.components.ServiceManager;
+import com.intellij.openapi.project.Project;
+import com.intellij.openapi.project.ProjectManager;
+import com.intellij.openapi.ui.Messages;
+import org.jetbrains.annotations.NotNull;
+
+/**
+ * @author duanledexianxianxian
+ * @date 2019/10/11 0:08
+ * @since 1.0.0
+ */
+public class MaxProject implements ProjectComponent {
+    public MaxProject(Project project) {
+    }
+
+    @Override
+    public void projectOpened() {
+// called when project is opened
+        MyCounter CommandCounter = ServiceManager.getService(MyCounter.class);
+
+        if (CommandCounter.increaseCounter() == -1) {
+            Messages.showMessageDialog(
+                    "The maximum number of opened projects exceeds " + AppConstants.MAX_CNT +
+                            " projects!", "Error", Messages.getErrorIcon());
+            ProjectManager PM = ProjectManager.getInstance();
+            Project[] AllProjects = PM.getOpenProjects();
+            Project project = AllProjects[AllProjects.length - 1];
+            PM.closeProject(project);
+        }
+    }
+
+    @Override
+    public void projectClosed() {
+        // called when project is being closed
+        MyCounter commandCounter = ServiceManager.getService(MyCounter.class);
+        commandCounter.decreaseCounter();
+    }
+
+    @Override
+    public void initComponent() {
+        // TODO: insert component initialization logic here
+    }
+
+    @Override
+    public void disposeComponent() {
+        // TODO: insert component disposal logic here
+    }
+
+    @NotNull
+    @Override
+    public String getComponentName() {
+        return "MaxProject";
+    }
+}

src/com/duanledexianxianxian/plugin/constant/AppConstants.java

+package com.duanledexianxianxian.plugin.constant;
+
+/**
+ * @author duanledexianxianxian
+ * @date 2019/10/11 0:24
+ * @since 1.0.0
+ */
+public class AppConstants {
+    public static int MAX_CNT = 1;
+
+}

src/com/duanledexianxianxian/plugin/service/application/MyCounter.java

+package com.duanledexianxianxian.plugin.service.application;
+
+import com.intellij.openapi.components.ServiceManager;
+
+/**
+ * The interface My counter.
+ */
+public interface MyCounter {
+
+    /**
+     * Gets instance.
+     *
+     * @return the instance
+     */
+    static MyCounter getInstance() {
+        return ServiceManager.getService(MyCounter.class);
+    }
+
+    /**
+     * Increase counter int.
+     *
+     * @return the int
+     */
+    int increaseCounter();
+
+    /**
+     * Decrease counter int.
+     *
+     * @return the int
+     */
+    int decreaseCounter();
+}

src/com/duanledexianxianxian/plugin/service/application/SampleApplication.java

+package com.duanledexianxianxian.plugin.service.application;
+
+import com.intellij.openapi.components.ServiceManager;
+
+/**
+ * @author fengyuchenglun
+ */
+public interface SampleApplication {
+    static SampleApplication getInstance() {
+        return ServiceManager.getService(SampleApplication.class);
+    }
+}

src/com/duanledexianxianxian/plugin/service/application/impl/MyCounterImpl.java

+package com.duanledexianxianxian.plugin.service.application.impl;
+
+import com.duanledexianxianxian.plugin.service.application.MyCounter;
+
+import static com.duanledexianxianxian.plugin.constant.AppConstants.MAX_CNT;
+
+/**
+ * The type My counter.
+ *
+ * @author fengyuchenglun
+ * @version 1.0.0
+ */
+public class MyCounterImpl implements MyCounter {
+    /**
+     * Sets the maximum allowed number of opened projects.
+     */
+    private int count = 0;
+
+    /**
+     * Instantiates a new My counter.
+     */
+    public MyCounterImpl() {
+    }
+
+    /**
+     * Increase counter int.
+     *
+     * @return the int
+     */
+    @Override
+    public int increaseCounter() {
+        count++;
+        return (count > MAX_CNT) ? -1 : count;
+    }
+
+    /**
+     * Decrease counter int.
+     *
+     * @return the int
+     */
+    @Override
+    public int decreaseCounter() {
+        count--;
+        return (count > MAX_CNT) ? -1 : count;
+    }
+}

src/com/duanledexianxianxian/plugin/service/application/impl/SampleApplicationImpl.java

+package com.duanledexianxianxian.plugin.service.application.impl;
+
+import com.duanledexianxianxian.plugin.service.application.SampleApplication;
+
+/**
+ * @author fengyuchenglun
+ */
+public class SampleApplicationImpl implements SampleApplication {
+
+}