App Inventor has introduced “copy and paste” of code blocks. Now you can copy blocks of code within a current screen, or from one screen to another screen, or even between projects. This is great news!
Look for the “backpack” icon at upper right of the blocks Viewer screen:
Select a block or blocks with the mouse pointer, and then click and drag the selected blocks into the backpack. A copy of the blocks are placed into the backpack and your original blocks also remain in the editing window.
Click on the backpack icon and it displays the code blocks currently stored in the backpack:
Click on the code block in the backpack (at right) and drag it into the Blocks Viewer. That is all you need to do to copy blocks.
Use this feature to copy blocks within your current screen, or to copy blocks from one screen to another screen, or to copy blocks from one app to another app.
You can put several blocks into the backpack, and then select only the ones you wish to copy over to another blocks Viewer.
How do you empty the backpack? It seems the only way to empty the backpack of saved items is to close the editing windows, go back to the MIT App Inventor home page (http://appinventor.mit.edu/) and select the Create apps! button to re-enter the designer and blocks editor.
Regardless, this is a GREAT NEW FEATURE! Thanks MIT App Inventor team!