con trỏ ngoại lệ Null với giao diện tùy chỉnh trong cách bố trí xml

Question

Dưới đây là các mã giao diện tùy chỉnh mà mang lại cho tôi một ngoại lệ con trỏ null trong tab bố trí của XML trong đó sử dụng quan điểm này:

public class BoardView extends View { 

    // Drawables for the board boxes, the playable zone 
    public Drawable[][] block = new Drawable[20][10]; 
    // Drawables for the wall (yes, it's done with tiles) 
    public Drawable[] wall = new Drawable[102]; 
    // Drawable for the background, and boolean for drawing it or not 
    Drawable mbg; 
    boolean bg = false; 
    // Context and canvas to be used along the class 
    Context context; 
    Canvas c; 

    /*************************************************/ 
    /* Class constructor **************************** */ 
    /*************************************************/ 
    /* Defines the context and the canvas *********** */ 
    /*************************************************/ 
    public BoardView(Context cont, AttributeSet attrs) { 
     super(cont, attrs); 
     context = cont; 
    } 

    /*************************************************/ 
    /* Initializes drawables for playable boxes ***** */ 
    /*************************************************/ 
    /* Must be initialized one by one from the Game * */ 
    /* activity, passing all the parameters ********* */ 
    /*************************************************/ 
    public void initialize(int i, int j, int left, int top, int side) { 
     block[i][j] = context.getResources().getDrawable(R.drawable.alpha); 
     block[i][j].setBounds(left, top, left + side, top + side); 
    } 

    /*************************************************/ 
    /* Draws the board wall ************************* */ 
    /*************************************************/ 
    /* Needs the top-left point of the board frame ** */ 
    /* and the width of the wall ******************** */ 
    /*************************************************/ 
    public void createWall(int left, int top, int side) { 
     int i = 0, x, y; 
     x = left - side/2; 
     y = top; 
     // The left wall 
     while (i < 40) { 
      wall[i] = context.getResources().getDrawable(R.drawable.brick); 
      wall[i].setBounds(x, y, x + side/2, y + side/2); 
      y = y + side/2; 
      i = i + 1; 
     } 
     x = left + side * 10; 
     y = top; 
     // The right wall 
     while (i < 80) { 
      wall[i] = context.getResources().getDrawable(R.drawable.brick); 
      wall[i].setBounds(x, y, x + side/2, y + side/2); 
      y = y + side/2; 
      i = i + 1; 
     } 
     x = left - side/2; 
     // The floor 
     while (i < 102) { 
      wall[i] = context.getResources().getDrawable(R.drawable.brick); 
      wall[i].setBounds(x, y, x + side/2, y + side/2); 
      x = x + side/2; 
      i = i + 1; 
     } 
    } 

    /*************************************************/ 
    /* Draws the board background ******************* */ 
    /*************************************************/ 
    /* Needs the top-left point of the board frame ** */ 
    /* and the width of the wall ******************** */ 
    /*************************************************/ 
    public void createBg(int left, int top, int side) { 
     // Set board background (if any) 
     bg = false; 
     int bgn = 1 + (int) (Math.random() * 19); 
     switch (bgn) { 
     case 1: 
      mbg = getResources().getDrawable(R.drawable.bg1); 
      break; 
     case 2: 
      mbg = getResources().getDrawable(R.drawable.bg2); 
      break; 
     case 3: 
      mbg = getResources().getDrawable(R.drawable.bg3); 
      break; 
     case 4: 
      mbg = getResources().getDrawable(R.drawable.bg4); 
      break; 
     case 5: 
      mbg = getResources().getDrawable(R.drawable.bg5); 
      break; 
     case 6: 
      mbg = getResources().getDrawable(R.drawable.bg6); 
      break; 
     case 7: 
      mbg = getResources().getDrawable(R.drawable.bg7); 
      break; 
     case 8: 
      mbg = getResources().getDrawable(R.drawable.bg8); 
      break; 
     case 9: 
      mbg = getResources().getDrawable(R.drawable.bg9); 
      break; 
     case 10: 
      mbg = getResources().getDrawable(R.drawable.bg11); 
      break; 
     case 11: 
      mbg = getResources().getDrawable(R.drawable.bg11); 
      break; 
     case 12: 
      mbg = getResources().getDrawable(R.drawable.bg12); 
      break; 
     case 13: 
      mbg = getResources().getDrawable(R.drawable.bg13); 
      break; 
     case 14: 
      mbg = getResources().getDrawable(R.drawable.bg14); 
      break; 
     case 15: 
      mbg = getResources().getDrawable(R.drawable.bg15); 
      break; 
     case 16: 
      mbg = getResources().getDrawable(R.drawable.bg16); 
      break; 
     case 17: 
      mbg = getResources().getDrawable(R.drawable.bg17); 
      break; 
     case 18: 
      mbg = getResources().getDrawable(R.drawable.bg18); 
      break; 
     case 19: 
      mbg = getResources().getDrawable(R.drawable.bg19); 
      break; 
     } 
     mbg.setBounds((int) (left), (int) (top), (int) (left + side * 10), 
       (int) (top + 20 * side)); 
    } 

    /*************************************************/ 
    /* Draws the board ****************************** */ 
    /*************************************************/ 
    /* Draws the walls, the bg and all the boxes **** */ 
    /*************************************************/ 
    @Override 
    protected void onDraw(Canvas canvas) { 
     c = canvas; 
     super.onDraw(canvas); 
     if (bg) 
      mbg.draw(canvas); 
     for (int i = 0; i < 102; i++) 
      wall[i].draw(c); 
     for (int i = 0; i < 20; i++) 
      for (int j = 0; j < 10; j++) { 
       block[i][j].draw(canvas); 
      } 
     // Actually draw 
     invalidate(); 
    } 

    /*************************************************/ 
    /* Canvas getter ******************************** */ 
    /*************************************************/ 
    public Canvas getCanvas() { 
     return c; 
    } 

    /*************************************************/ 
    /* Colors a box ********************************* */ 
    /*************************************************/ 
    /* Changes the drawable for the indicated box to */ 
    /* to 'c'. Can also be COLOR_NONE to undraw ***** */ 
    /*************************************************/ 
    public void setColor(int i, int j, byte c) { 
     Rect rect; 
     rect = block[i][j].getBounds(); 
     switch (c) { 
     case Values.COLOR_NONE: 
      block[i][j] = context.getResources().getDrawable(R.drawable.alpha); 
      ; 
      break; 
     case Values.COLOR_RED: 
      block[i][j] = context.getResources().getDrawable(
        R.drawable.block_red); 
      break; 
     case Values.COLOR_GREEN: 
      block[i][j] = context.getResources().getDrawable(
        R.drawable.block_green); 
      break; 
     case Values.COLOR_BLUE: 
      block[i][j] = context.getResources().getDrawable(
        R.drawable.block_blue); 
      break; 
     case Values.COLOR_YELLOW: 
      block[i][j] = context.getResources().getDrawable(
        R.drawable.block_yellow); 
      break; 
     case Values.COLOR_PINK: 
      block[i][j] = context.getResources().getDrawable(
        R.drawable.block_pink); 
      break; 
     case Values.COLOR_PURPLE: 
      block[i][j] = context.getResources().getDrawable(
        R.drawable.block_purple); 
      break; 
     case Values.COLOR_WHITE: 
      block[i][j] = context.getResources().getDrawable(
        R.drawable.block_white); 
      break; 
     } 
     block[i][j].setBounds(rect); 
    } 
} 

và đây là nhật ký lỗi:

java.lang.NullPointerException 
    at com.seavenois.tetris.BoardView.onDraw(BoardView.java:166) 
    at android.view.View.draw(View.java:6880) 
    at android.view.ViewGroup.drawChild(ViewGroup.java:1646) 
    at android.view.ViewGroup.dispatchDraw(ViewGroup.java:1373) 
    at android.view.ViewGroup.drawChild(ViewGroup.java:1644) 
    at android.view.ViewGroup.dispatchDraw(ViewGroup.java:1373) 
    at android.view.ViewGroup.drawChild(ViewGroup.java:1644) 
    at android.view.ViewGroup.dispatchDraw(ViewGroup.java:1373) 
    at android.view.ViewGroup.drawChild(ViewGroup.java:1644) 
    at android.view.ViewGroup.dispatchDraw(ViewGroup.java:1373) 
    at android.view.ViewGroup.drawChild(ViewGroup.java:1644) 
    at android.view.ViewGroup.dispatchDraw(ViewGroup.java:1373) 
    at android.view.View.draw(View.java:6883) 
    at android.view.ViewGroup.drawChild(ViewGroup.java:1646) 
    at android.view.ViewGroup.dispatchDraw(ViewGroup.java:1373) 
    at android.view.View.draw(View.java:6883) 
    at com.android.layoutlib.bridge.impl.RenderSessionImpl.render(RenderSessionImpl.java:466) 
    at com.android.layoutlib.bridge.Bridge.createSession(Bridge.java:320) 
    at com.android.ide.common.rendering.LayoutLibrary.createSession(LayoutLibrary.java:325) 
    at com.android.ide.eclipse.adt.internal.editors.layout.gle2.RenderService.createRenderSession(RenderService.java:372) 
    at com.android.ide.eclipse.adt.internal.editors.layout.gle2.GraphicalEditorPart.renderWithBridge(GraphicalEditorPart.java:1640) 
    at com.android.ide.eclipse.adt.internal.editors.layout.gle2.GraphicalEditorPart.recomputeLayout(GraphicalEditorPart.java:1391) 
    at com.android.ide.eclipse.adt.internal.editors.layout.gle2.GraphicalEditorPart.activated(GraphicalEditorPart.java:1165) 
    at com.android.ide.eclipse.adt.internal.editors.layout.LayoutEditorDelegate.partActivated(LayoutEditorDelegate.java:734) 
    at com.android.ide.eclipse.adt.internal.editors.layout.LayoutEditorDelegate.partBroughtToTop(LayoutEditorDelegate.java:744) 
    at org.eclipse.ui.internal.PartListenerList$2.run(PartListenerList.java:87) 
    at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:42) 
    at org.eclipse.core.runtime.Platform.run(Platform.java:888) 
    at org.eclipse.ui.internal.PartListenerList.fireEvent(PartListenerList.java:57) 
    at org.eclipse.ui.internal.PartListenerList.firePartBroughtToTop(PartListenerList.java:85) 
    at org.eclipse.ui.internal.PartService.firePartBroughtToTop(PartService.java:208) 
    at org.eclipse.ui.internal.WorkbenchPagePartList.firePartBroughtToTop(WorkbenchPagePartList.java:76) 
    at org.eclipse.ui.internal.WorkbenchPagePartList.fireActiveEditorChanged(WorkbenchPagePartList.java:52) 
    at org.eclipse.ui.internal.PartList.setActiveEditor(PartList.java:162) 
    at org.eclipse.ui.internal.WorkbenchPage.makeActiveEditor(WorkbenchPage.java:1355) 
    at org.eclipse.ui.internal.WorkbenchPage.setActivePart(WorkbenchPage.java:3629) 
    at org.eclipse.ui.internal.WorkbenchPage.requestActivation(WorkbenchPage.java:3159) 
    at org.eclipse.ui.internal.PartPane.requestActivation(PartPane.java:279) 
    at org.eclipse.ui.internal.EditorPane.requestActivation(EditorPane.java:98) 
    at org.eclipse.ui.internal.PartPane.setFocus(PartPane.java:325) 
    at org.eclipse.ui.internal.EditorPane.setFocus(EditorPane.java:127) 
    at org.eclipse.ui.internal.PartStack.presentationSelectionChanged(PartStack.java:837) 
    at org.eclipse.ui.internal.PartStack.access$1(PartStack.java:823) 
    at org.eclipse.ui.internal.PartStack$1.selectPart(PartStack.java:137) 
    at org.eclipse.ui.internal.presentations.util.TabbedStackPresentation$1.handleEvent(TabbedStackPresentation.java:133) 
    at org.eclipse.ui.internal.presentations.util.AbstractTabFolder.fireEvent(AbstractTabFolder.java:269) 
    at org.eclipse.ui.internal.presentations.util.AbstractTabFolder.fireEvent(AbstractTabFolder.java:278) 
    at org.eclipse.ui.internal.presentations.defaultpresentation.DefaultTabFolder.access$1(DefaultTabFolder.java:1) 
    at org.eclipse.ui.internal.presentations.defaultpresentation.DefaultTabFolder$2.handleEvent(DefaultTabFolder.java:88) 
    at org.eclipse.swt.widgets.EventTable.sendEvent(EventTable.java:84) 
    at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1053) 
    at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1077) 
    at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1062) 
    at org.eclipse.swt.widgets.Widget.notifyListeners(Widget.java:774) 
    at org.eclipse.swt.custom.CTabFolder.setSelection(CTabFolder.java:2746) 
    at org.eclipse.swt.custom.CTabFolder.onMouse(CTabFolder.java:1433) 
    at org.eclipse.swt.custom.CTabFolder$1.handleEvent(CTabFolder.java:257) 
    at org.eclipse.swt.widgets.EventTable.sendEvent(EventTable.java:84) 
    at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1053) 
    at org.eclipse.swt.widgets.Display.runDeferredEvents(Display.java:4165) 
    at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:3754) 
    at org.eclipse.ui.internal.Workbench.runEventLoop(Workbench.java:2701) 
    at org.eclipse.ui.internal.Workbench.runUI(Workbench.java:2665) 
    at org.eclipse.ui.internal.Workbench.access$4(Workbench.java:2499) 
    at org.eclipse.ui.internal.Workbench$7.run(Workbench.java:679) 
    at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:332) 
    at org.eclipse.ui.internal.Workbench.createAndRunWorkbench(Workbench.java:668) 
    at org.eclipse.ui.PlatformUI.createAndRunWorkbench(PlatformUI.java:149) 
    at org.eclipse.ui.internal.ide.application.IDEApplication.start(IDEApplication.java:123) 
    at org.eclipse.equinox.internal.app.EclipseAppHandle.run(EclipseAppHandle.java:196) 
    at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.runApplication(EclipseAppLauncher.java:110) 
    at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.start(EclipseAppLauncher.java:79) 
    at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:344) 
    at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:179) 
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) 
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source) 
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source) 
    at java.lang.reflect.Method.invoke(Unknown Source) 
    at org.eclipse.equinox.launcher.Main.invokeFramework(Main.java:622) 
    at org.eclipse.equinox.launcher.Main.basicRun(Main.java:577) 
    at org.eclipse.equinox.launcher.Main.run(Main.java:1410) 
    at org.eclipse.equinox.launcher.Main.main(Main.java:1386) 

đây là dòng 166 của BoardView.java:

wall[i].draw(c); 

Làm thế nào tôi có thể sửa lỗi này? Tôi nhận được mã này từ mã nguồn tetris và tôi muốn nghiên cứu điều này để tham khảo trong tương lai nhưng tôi không thể xem bố cục của trò chơi

Answer 1

Bạn đang không làm bất kỳ NULL check-in onDraw() của bạn.

Có kiểm tra NULL sẽ giúp bạn tạo mã ổn định hơn và giúp bạn tìm thấy vấn đề của mình nhanh hơn.

tôi sẽ thêm vào một số NULL kiểm tra như dưới đây:

protected void onDraw(Canvas canvas) { 
    if (canvas != null) { 
     c = canvas; 
     super.onDraw(canvas); 
     if (bg) { 
      if (mbg != null) { 
       mbg.draw(canvas); 
      } else { 
       /* 
       * Handle null value 
       * print to logcat this was null 
       */ 
      } 
     } 
     for (int i = 0; i < 102; i++) { 
      if (wall[i] != null) { 
       wall[i].draw(c); 
      } else { 
       /* 
       * Handle null value 
       * print to logcat this was null 
       */ 
      } 
     } 
     for (int i = 0; i < 20; i++) { 
      for (int j = 0; j < 10; j++) { 
       if (block[i][j] != null) { 
        block[i][j].draw(canvas); 
       } else { 
        /* 
        * Handle null value 
        * print to logcat this was null 
        */ 
       } 
      } 
     } 
     //Actually draw 
     invalidate(); 
    } else { 
     /* 
     * Handle null value 
     * print to logcat this was null 
     */ 
    } 

} 

Answer 2

Tôi không thấy cuộc gọi thực tế của phương thức khởi tạo.

Chẳng hạn như:

initialize(i, j, left, top, side); 

Vì vậy, tôi đoán bạn làm điều đó từ bên ngoài và bỏ lỡ một cái gì đó để hoặc là một bức tường, khối hoặc MBG vẫn null.

Có thể thêm một số mã về cách bạn sử dụng và khởi tạo chế độ xem của bạn nếu gợi ý đó không đủ.

(Hoặc, nhưng thats hy vọng không phải như vậy, tôi đã sai lầm!)