feat(gui): save the class tree width and restore it upon jadx-gui start (PR #606)

jadx-gui/src/main/java/jadx/gui/settings/JadxSettings.java

 package jadx.gui.settings;
 
-import java.awt.*;
+import java.awt.Font;
+import java.awt.GraphicsDevice;
+import java.awt.GraphicsEnvironment;
+import java.awt.Window;
 import java.nio.file.Path;
 import java.nio.file.Paths;
 import java.util.ArrayList;
@@ -55,6 +58,10 @@ public class JadxSettings extends JadxCLIArgs {
 
 	private Map<String, WindowLocation> windowPos = new HashMap<>();
 	private int mainWindowExtendedState = JFrame.NORMAL;
+	/**
+	 * UI setting: the width of the tree showing the classes, resources, ...
+	 */
+	private int treeWidth = 130;
 
 	private int settingsVersion = 0;
 
@@ -305,6 +312,15 @@ public class JadxSettings extends JadxCLIArgs {
 		this.exportAsGradleProject = exportAsGradleProject;
 	}
 
+	public int getTreeWidth() {
+		return treeWidth;
+	}
+
+	public void setTreeWidth(int treeWidth) {
+		this.treeWidth = treeWidth;
+		partialSync(settings -> settings.treeWidth = JadxSettings.this.treeWidth);
+	}
+
 	public Font getFont() {
 		if (fontStr.isEmpty()) {
 			return DEFAULT_FONT;

jadx-gui/src/main/java/jadx/gui/ui/MainWindow.java

 package jadx.gui.ui;
 
-import java.awt.*;
+import java.awt.BorderLayout;
+import java.awt.Component;
+import java.awt.Dimension;
+import java.awt.DisplayMode;
+import java.awt.Font;
+import java.awt.GraphicsDevice;
+import java.awt.GraphicsEnvironment;
 import java.awt.dnd.DnDConstants;
 import java.awt.dnd.DropTarget;
 import java.awt.event.ActionEvent;
@@ -23,7 +29,27 @@ import java.util.Locale;
 import java.util.Timer;
 import java.util.TimerTask;
 
-import javax.swing.*;
+import javax.swing.AbstractAction;
+import javax.swing.Action;
+import javax.swing.Box;
+import javax.swing.ImageIcon;
+import javax.swing.JCheckBoxMenuItem;
+import javax.swing.JFileChooser;
+import javax.swing.JFrame;
+import javax.swing.JMenu;
+import javax.swing.JMenuBar;
+import javax.swing.JMenuItem;
+import javax.swing.JOptionPane;
+import javax.swing.JPanel;
+import javax.swing.JPopupMenu;
+import javax.swing.JScrollPane;
+import javax.swing.JSplitPane;
+import javax.swing.JToggleButton;
+import javax.swing.JToolBar;
+import javax.swing.JTree;
+import javax.swing.ProgressMonitor;
+import javax.swing.SwingUtilities;
+import javax.swing.WindowConstants;
 import javax.swing.event.MenuEvent;
 import javax.swing.event.MenuListener;
 import javax.swing.event.TreeExpansionEvent;
@@ -102,6 +128,7 @@ public class MainWindow extends JFrame {
 	private transient Action saveProjectAction;
 
 	private JPanel mainPanel;
+	private JSplitPane splitPane;
 
 	private JTree tree;
 	private DefaultTreeModel treeModel;
@@ -140,6 +167,7 @@ public class MainWindow extends JFrame {
 	public void init() {
 		pack();
 		setLocationAndPosition();
+		splitPane.setDividerLocation(settings.getTreeWidth());
 		heapUsageBar.setVisible(settings.isShowHeapUsageBar());
 		setVisible(true);
 		setDefaultCloseOperation(WindowConstants.DO_NOTHING_ON_CLOSE);
@@ -772,8 +800,9 @@ public class MainWindow extends JFrame {
 	}
 
 	private void initUI() {
+		setMinimumSize(new Dimension(200, 150));
 		mainPanel = new JPanel(new BorderLayout());
-		JSplitPane splitPane = new JSplitPane();
+		splitPane = new JSplitPane();
 		splitPane.setResizeWeight(SPLIT_PANE_RESIZE_WEIGHT);
 		mainPanel.add(splitPane);
 
@@ -840,11 +869,15 @@ public class MainWindow extends JFrame {
 		progressPane = new ProgressPanel(this, true);
 
 		JPanel leftPane = new JPanel(new BorderLayout());
-		leftPane.add(new JScrollPane(tree), BorderLayout.CENTER);
+		JScrollPane treeScrollPane = new JScrollPane(tree);
+		treeScrollPane.setMinimumSize(new Dimension(100, 150));
+
+		leftPane.add(treeScrollPane, BorderLayout.CENTER);
 		leftPane.add(progressPane, BorderLayout.PAGE_END);
 		splitPane.setLeftComponent(leftPane);
 
 		tabbedPane = new TabbedPane(this);
+		tabbedPane.setMinimumSize(new Dimension(150, 150));
 		splitPane.setRightComponent(tabbedPane);
 
 		new DropTarget(this, DnDConstants.ACTION_COPY, new MainDropTarget(this));
@@ -931,6 +964,7 @@ public class MainWindow extends JFrame {
 		if (!ensureProjectIsSaved()) {
 			return;
 		}
+		settings.setTreeWidth(splitPane.getDividerLocation());
 		settings.saveWindowPos(this);
 		settings.setMainWindowExtendedState(getExtendedState());
 		cancelBackgroundJobs();