[問題] 在JPanel上面繪圖的完整準備工作?

[olys (查無暱稱)]

一直找不到一個完整的教學 =_=........


現在好像只有看到

1.要創一個新的class是繼承JPanel, 裡面到底要加什麼不知道,
  然後宣告Panel時要用那個Class
2.要加一行 Graphics g = gPanel.getGraphics(); , 要放在哪裡不知道

然後以上備齊似乎就可以g.drawline等等亂畫了

可是完整的過程是怎麼樣啊 orz

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→ kanandg1:主要是取得該元件的Graphics，取得後就能畫了
→ kanandg1:可以寫一個class繼承JPanel，並Override paint(Graphics)
→ kanandg1:或是用getGraphics()來取得某個JPanel的Graphics
→ olys:所以我只要2的那一行出來以下就能任意畫畫了? 要放在哪裡呢?
→ kanandg1:要放在能存取到gPanel的地方..此method是public的
→ kanandg1:我比較建議第一種方法
→ olys:第一種方法請問能說詳細嗎? 剛剛試了方法2都會執行error
→ kanandg1:如果此元件是不可視的話，getGraphics會return null
→ olys:意思是先用gPanel.setVisible(true)嗎? 還是error了orz
→ kanandg1:有出現在畫面上嗎?如果不是這個問題就貼詳細的錯誤出來~
IWAV0052E Invocation Target Exception creating Voronoi.Voronoi
java.lang.reflect.InvocationTargetException
        at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
        at sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source)
        at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source)
        at java.lang.reflect.Constructor.newInstance(Unknown Source)
        at
org.eclipse.ve.internal.java.vce.launcher.remotevm.JFCLauncher$1.run(JFCLauncher.java:59)
        at java.awt.event.InvocationEvent.dispatch(Unknown Source)
        at java.awt.EventQueue.dispatchEvent(Unknown Source)
        at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
        at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
        at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
        at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
        at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
        at java.awt.EventDispatchThread.run(Unknown Source)
Caused by: java.lang.NullPointerException
        at Voronoi.Voronoi$2.<init>(Voronoi.java:60)
        at Voronoi.Voronoi.<init>(Voronoi.java:59)
        ... 13 more
※ 編輯: olys            來自: 114.47.82.26         (11/13 19:00)