高中信息技术选修1：算法与程序设计 4.6 综合活动：问题求解

ChapterIIPaintPotPartIDipyourfingerintoavirtualpaintpottodrawin

thatcolor.Dragyourfingeralongthescreentodrawaline.Pokethescreentomakedots.Usethebuttonatthebottomtowipethescreen

clean.Changethedotsizetolargeorsmallwiththe

buttonsatthebottom.Takeapicturewiththecameraandthendrawon

thatpicture.WiththePaintPotappyoucanUsingtheCanvascomponentfordrawing.Handlingtouchanddrageventsonthephone’ssurface.Controllingscreenlayoutwitharrangementcomponents.Usingeventhandlersthattakearguments.Definingvariablestorememberthingslikethedotsizetheuserhaschosenfordrawing.WhatYou’llLearnThenameyouchooseforyourprojectasyouworkonit.Thiswillalsobethenameoftheapplicationwhenyoupackageitforthephone.NotethatyoucanclickSaveAsintheComponentDesignertostartanewversionorrenameaproject.ThecomponentnameScreen1,whichyou’llseeinthepanelthatliststheapplication’scomponents.Youcan’tchangethisnameinthecurrentversionofAppInventor.Thetitleofthescreen,whichiswhatyou’llseeinthephone’stitlebar.ThisstartsoutbeingScreen1,whichiswhatyouusedinHelloPurr.Butyoucanchangeit,aswejustdidforPaintPot.TherearethreekeynamesinAppInventorUsingmoremeaningfulnamesmakesyourprojectsmorereadable,anditwillreallyhelpwhenyoumovetotheBlocksEditorandmustrefertothecomponentsbyname.Inthisbook,we’llusetheconventionofhavingthecomponentnameendwithitstype(forexample,

RedButton).UsemeaningfulnamesChapterIIPaintPotPartIIOntherightsideoftheDrawingCanvas.DrawCircleblock,you’llseefourslotsfortheargumentsweneedtofillin:x,y,andr.Andafillslot.Thexandyargumentsspecifythelocationwherethecircleshouldbedrawn,andrdeterminestheradius(orsize)ofthecircle.Ifthefillslotistrue,thenthecircleisvisible,ifisfalse,thecircleisinvisible.DrawingcircleAtouchiswhenyouplaceyourfingeronthecanvasandliftitwithoutmovingit.Adragiswhenyouplaceyourfingeronthecanvasandmoveitwhilekeepingitincontactwiththescreen.TouchOrDragOntherightsideoftheDrawingCanvas.DrawCircleblock,you’llseethreeslotsfortheargumentsweneedtofillin:x,y,andr.Thexandyargumentsspecifythelocationwherethecircleshouldbedrawn,andrdeterminestheradius(orsize)ofthecircle.DrawingLineOntherightsideoftheDrawingCanvas.DrawLineblock,you’llseefourslotsfortheargumentsweneedtofillin:x1,y1,x2,y2.Twoforeachpointthatdeterminestheline:(x1,y1)isonepoint,while(x2,y2)istheother.ChapterIIPaintPotPartIIIColorbuttonsAdding