Added code to enable / disable the Edit->Paste menu item when the contents of the clipboard change

git-svn-id: file:///srv/svn/repos/haiku/trunk/current@5413 a95241bf-73f2-0310-859d-f6bbb57e9c96

src/apps/showimage/ShowImageApp.cpp

@@ -29,6 +29,8 @@
 #include <stdio.h>
 #include <Alert.h>
 #include <FilePanel.h>
+#include <String.h>
+#include <Clipboard.h>
 
 #include "ShowImageConstants.h"
 #include "ShowImageApp.h"
@@ -68,6 +70,9 @@ ShowImageApp::ReadyToRun()
 		// (paths supplied on the command line)
 		// start checking the number of open windows
 		StartPulse();
+
+	be_clipboard->StartWatching(be_app_messenger);
+		// tell the clipboard to notify this app when its contents change
 }
 
 void
@@ -131,6 +136,10 @@ ShowImageApp::MessageReceived(BMessage *pmsg)
 		case MSG_UPDATE_RECENT_DOCUMENTS:
 			BroadcastToWindows(MSG_UPDATE_RECENT_DOCUMENTS);
 			break;
+			
+		case B_CLIPBOARD_CHANGED:
+			CheckClipboard();
+			break;
 
 		default:
 			BApplication::MessageReceived(pmsg);
@@ -170,3 +179,52 @@ ShowImageApp::BroadcastToWindows(uint32 what)
 		msgr.SendMessage(what);
 	}
 }
+
+void
+ShowImageApp::BroadcastToWindows(BMessage *pmsg)
+{
+	const int32 n = CountWindows();
+	for (int32 i = 0; i < n ; i ++) {
+		// BMessenger checks for us if BWindow is still a valid object
+		BMessenger msgr(WindowAt(i));
+		msgr.SendMessage(pmsg);
+	}
+}
+
+void
+ShowImageApp::CheckClipboard()
+{
+	// Determines if the contents of the clipboard contain
+	// data that is useful to this application. 
+	// After checking the clipboard, a message is sent to
+	// all windows indicating that the clipboard has changed
+	// and whether or not the clipboard contains useful data.
+	bool bdata = false;
+ 
+	if (be_clipboard->Lock()) {	
+		BMessage *pclip;
+		if ((pclip = be_clipboard->Data()) != NULL) {
+			BString strClass;
+			if (pclip->FindString("class", &strClass) == B_OK) {
+				if (strClass == "BBitmap")
+					bdata = true;
+			}
+		}
+		
+		be_clipboard->Unlock(); 
+	}
+	
+	BMessage msg(MSG_CLIPBOARD_CHANGED);
+	msg.AddBool("data_available", bdata);
+	BroadcastToWindows(&msg);
+}
+
+void
+ShowImageApp::Quit()
+{
+	be_clipboard->StopWatching(be_app_messenger);
+		// tell clipboard we don't want anymore notification
+	
+	BApplication::Quit();
+}
+

src/apps/showimage/ShowImageApp.h

@@ -42,11 +42,14 @@ public:
 	virtual void ReadyToRun();
 	virtual void Pulse();
 	virtual void RefsReceived(BMessage *pmsg);
+	virtual void Quit();
 
 private:
 	void StartPulse();
 	void Open(const entry_ref *pref);
 	void BroadcastToWindows(uint32 what);
+	void BroadcastToWindows(BMessage *pmsg);
+	void CheckClipboard();
 
 	BFilePanel *fpOpenPanel;
 	bool fbPulseStarted;

src/apps/showimage/ShowImageConstants.h

@@ -40,6 +40,7 @@ const uint32 MSG_OUTPUT_TYPE		= 'BTMN';
 const uint32 MSG_SAVE_PANEL			= 'mFSP';
 const uint32 MSG_CLEAR_SELECT		= 'mCSL';
 const uint32 MSG_SELECT_ALL			= 'mSAL';
+const uint32 MSG_CLIPBOARD_CHANGED	= 'mCLP';
 const uint32 MSG_DITHER_IMAGE		= 'mDIM';
 const uint32 MSG_UPDATE_STATUS		= 'mUPS';
 const uint32 MSG_SELECTION			= 'mSEL';

src/apps/showimage/ShowImageWindow.cpp

@@ -128,6 +128,10 @@ ShowImageWindow::ShowImageWindow(const entry_ref *pref)
 		// exit if file could not be opened
 		Quit();
 	}
+	
+	// Tell application object to query the clipboard
+	// and tell this window if it contains interesting data or not
+	be_app_messenger.SendMessage(B_CLIPBOARD_CHANGED);
 }
 
 ShowImageWindow::~ShowImageWindow()
@@ -535,6 +539,17 @@ ShowImageWindow::MessageReceived(BMessage *pmsg)
 			}
 			break;
 		}
+		
+		case MSG_CLIPBOARD_CHANGED:
+		{
+			// The app sends this message after it examines
+			// the clipboard in response to a B_CLIPBOARD_CHANGED
+			// message
+			bool bdata;
+			if (pmsg->FindBool("data_available", &bdata) == B_OK)
+				EnableMenuItem(fpBar, B_PASTE, bdata);
+			break;
+		}
 
 		case B_UNDO:
 			break;