Android: попытка вызвать виртуальный метод ссылка на нулевой объект

Question

У меня есть некоторые проблемы. Здесь, в моем коде, я пытаюсь перерисовать чертеж, нарисованный на борту, на экране. но я получаю исключение Null Object Reference

В моем коде растровые изображения - это растровый архаист.

Вот мой код saveInstanceState

@Override 
protected void onSaveInstanceState(Bundle outState) { 
    super.onSaveInstanceState(outState); 
    bitArrayStore(j); 
    outState.putParcelableArrayList("Bits", bitmaps); 
    outState.putInt("j", j); 
} 

Вот bitArrayStore()

public void bitArrayStore(int k) { 

    if (drawView.canvasBitmap.sameAs(drawView.emptyBitmap)) { 
     flag = true; 
    } else { 

     try { 
      if (flag1 == false) { 
       drawView.buildDrawingCache(); 
       drawView.setDrawingCacheQuality(View.DRAWING_CACHE_QUALITY_HIGH); 
       bitmaps.set(k, Bitmap.createBitmap(drawView.getDrawingCache())); 

      } else { 
       bitmaps.add(k, Bitmap.createBitmap(drawView.getDrawingCache())); 
       flag1 = false; 
      } 
     } catch (IndexOutOfBoundsException e) { 
      bitmaps.add(k, Bitmap.createBitmap(drawView.getDrawingCache())); 

     } 
     drawView.destroyDrawingCache(); 

    } 
} 

Вот мой onRestoreInstanceState код

@Override 
protected void onRestoreInstanceState(Bundle savedInstanceState) { 
    super.onRestoreInstanceState(savedInstanceState); 
    bitmaps=savedInstanceState.getParcelableArrayList("Bits"); 
    j = savedInstanceState.getInt("j"); 
    redraww(); 
} 

мой метод redraww

public void redraww() 
    { 
     try{ 

      drawView.redraw(bitmaps, j); 
     }catch (IndexOutOfBoundsException e){ 
      drawView.startNew(); 
     } 

    } 

метод drawView.redraw() (Вот где я получу свое исключение. Я вошел его)

public void redraw(ArrayList<Bitmap> bits, int i) { 
    try { 

     drawCanvas.drawBitmap(bits.get(i), 0, 0, canvasPaint); 
     invalidate(); 
    }catch (NullPointerException e){ 
     Log.w("Notepad",e); 
    } 
} 

Вот мой журнал

10-25 09:58:19.826 12664-12664/org.notepad.notepad W/Notepad: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.graphics.Canvas.drawBitmap(android.graphics.Bitmap, float, float, android.graphics.Paint)' on a null object reference 
10-25 09:58:19.826 12664-12664/org.notepad.notepad W/Notepad:  at org.notepad.notepad.notespage.DrawingView.redraw(DrawingView.java:145) 
10-25 09:58:19.826 12664-12664/org.notepad.notepad W/Notepad:  at org.notepad.notepad.notespage.NewNote.redraww(NewNote.java:368) 
10-25 09:58:19.826 12664-12664/org.notepad.notepad W/Notepad:  at org.notepad.notepad.notespage.NewNote.onRestoreInstanceState(NewNote.java:395) 
10-25 09:58:19.826 12664-12664/org.notepad.notepad W/Notepad:  at android.app.Activity.performRestoreInstanceState(Activity.java:978) 
10-25 09:58:19.826 12664-12664/org.notepad.notepad W/Notepad:  at android.app.Instrumentation.callActivityOnRestoreInstanceState(Instrumentation.java:1162) 
10-25 09:58:19.826 12664-12664/org.notepad.notepad W/Notepad:  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2298) 
10-25 09:58:19.826 12664-12664/org.notepad.notepad W/Notepad:  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2387) 
10-25 09:58:19.826 12664-12664/org.notepad.notepad W/Notepad:  at android.app.ActivityThread.handleRelaunchActivity(ActivityThread.java:3947) 
10-25 09:58:19.826 12664-12664/org.notepad.notepad W/Notepad:  at android.app.ActivityThread.access$900(ActivityThread.java:151) 
10-25 09:58:19.826 12664-12664/org.notepad.notepad W/Notepad:  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1309) 
10-25 09:58:19.826 12664-12664/org.notepad.notepad W/Notepad:  at android.os.Handler.dispatchMessage(Handler.java:102) 
10-25 09:58:19.826 12664-12664/org.notepad.notepad W/Notepad:  at android.os.Looper.loop(Looper.java:135) 
10-25 09:58:19.826 12664-12664/org.notepad.notepad W/Notepad:  at android.app.ActivityThread.main(ActivityThread.java:5254) 
10-25 09:58:19.826 12664-12664/org.notepad.notepad W/Notepad:  at java.lang.reflect.Method.invoke(Native Method) 
10-25 09:58:19.826 12664-12664/org.notepad.notepad W/Notepad:  at java.lang.reflect.Method.invoke(Method.java:372) 
10-25 09:58:19.826 12664-12664/org.notepad.notepad W/Notepad:  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903) 
10-25 09:58:19.826 12664-12664/org.notepad.notepad W/Notepad:  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698) 

Чертеж не перерисовывается на поворот экрана вместо я получаю этот exception.I я не в состоянии решить. Пожалуйста, помогите ..

EDIT: Мой Java код программы

NewNote.java

public class NewNote extends AppCompatActivity implements View.OnClickListener { 


    private DrawingView drawView; 
    private ImageButton currPaint; 
    private float smallBrush = 5, mediumBrush = 10, largeBrush = 30; 
    String ucolor; 
    int i = 0, j = 0; 
    private boolean flag = false, flag1 = false; 
    ArrayList<Bitmap> bitmaps; 
    Bitmap[] bits; 
    @Bind(R.id.colornsize) 
    ViewGroup colorNsize; 
    @Bind(R.id.eraserdrawer) 
    ViewGroup eraserDrawer; 
    @Bind(R.id.blue_paint) 
    ImageButton bluePaint; 
    @Bind(R.id.small_brush) 
    ImageButton smallBtn; 
    @Bind(R.id.medium_brush) 
    ImageButton mediumBtn; 
    @Bind(R.id.large_brush) 
    ImageButton largeBtn; 
    @Bind(R.id.small_eraser) 
    ImageButton smallEraser; 
    @Bind(R.id.medium_eraser) 
    ImageButton mediumEraser; 
    @Bind(R.id.large_eraser) 
    ImageButton largeEraser; 
    @Bind(R.id.bottom_drawer) 
    ViewGroup btm; 
    @Bind(R.id.previousbtn) 
    ImageButton previousBtn; 
    @Bind(R.id.nextbtn) 
    ImageButton nextBtn; 
    @Bind(R.id.framelayout) 
    FrameLayout frameLayout; 


    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.notespage_newnote); 
     ButterKnife.bind(this); 
     Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar); 
     setSupportActionBar(toolbar); 
     getSupportActionBar().setDisplayHomeAsUpEnabled(true); 


     drawView = (DrawingView) findViewById(R.id.drawing); 
     currPaint = bluePaint; 
     currPaint.setImageResource(R.drawable.paint_pressed); 
     smallBrush = getResources().getInteger(R.integer.small_size); 
     mediumBrush = getResources().getInteger(R.integer.medium_size); 
     largeBrush = getResources().getInteger(R.integer.large_size); 
     drawView.setBrushSize(mediumBrush); 
     bitmaps = new ArrayList<Bitmap>(); 
     bits = new Bitmap[40]; 
     drawView.setDrawingCacheEnabled(true); 
     smallBtn.setOnClickListener(this); 
     mediumBtn.setOnClickListener(this); 
     largeBtn.setOnClickListener(this); 
     smallEraser.setOnClickListener(this); 
     mediumEraser.setOnClickListener(this); 
     largeEraser.setOnClickListener(this); 
     previousBtn.setOnClickListener(this); 
     nextBtn.setOnClickListener(this); 




     drawView.setOnTouchListener(new View.OnTouchListener() { 
      @Override 
      public boolean onTouch(View v, MotionEvent event) { 
       switch (event.getAction()) { 
        case MotionEvent.ACTION_DOWN: 
         btm.setVisibility(View.GONE); 
         break; 
        case MotionEvent.ACTION_UP: 
         btm.setVisibility(View.VISIBLE); 
         break; 
        default: 
         return false; 
       } 

       return false; 
      } 
     }); 


    } 


    public void paintClicked(View view) { 
     //use chosen color 
     drawView.setErase(false); 
     drawView.setBrushSize(drawView.getLastBrushSize()); 
     if (view != currPaint) { 
      //update color 
      ImageButton imgView = (ImageButton) view; 
      String color = view.getTag().toString(); 
      drawView.setColor(color); 

      imgView.setImageDrawable(getResources().getDrawable(R.drawable.paint_pressed)); 
      currPaint.setImageDrawable(getResources().getDrawable(R.drawable.paint)); 
      currPaint = (ImageButton) view; 
     } 
     hideDrawer(colorNsize); 
    } 

    @Override 
    public boolean onCreateOptionsMenu(Menu menu) { 
     getMenuInflater().inflate(R.menu.newnote_menu, menu); 
     return true; 
    } 

    @Override 
    public boolean onOptionsItemSelected(MenuItem item) { 
     // Handle action bar item clicks here. The action bar will 
     // automatically handle clicks on the Home/Up button, so long 
     // as you specify a parent activity in AndroidManifest.xml. 
     int id = item.getItemId(); 

     //noinspection SimplifiableIfStatement 
     if (id == R.id.clear_menuitem) { 
      hideDrawer(colorNsize); 
      hideDrawer(eraserDrawer); 
      AlertDialog.Builder newDialog = new AlertDialog.Builder(this); 
      newDialog.setTitle("Clear Board"); 
      newDialog.setMessage("Do you want to clear the board (you will lose the current drawing)?"); 
      newDialog.setPositiveButton("Yes", new DialogInterface.OnClickListener() { 
       public void onClick(DialogInterface dialog, int which) { 
        drawView.startNew(); 
        bitmaps.remove(j); 
        flag1 = true; 

        dialog.dismiss(); 
       } 
      }); 
      newDialog.setNegativeButton("Cancel", new DialogInterface.OnClickListener() { 
       public void onClick(DialogInterface dialog, int which) { 
        dialog.cancel(); 
       } 
      }); 
      newDialog.show(); 

      return true; 
     } else if (id == R.id.save_menuitem) { 
      hideDrawer(colorNsize); 
      hideDrawer(eraserDrawer); 
      bitArrayStore(j); 
      int k = 0; 
      try { 

       while (k <= bitmaps.size()) { 


        Bitmap m = null; 

        m = bitmaps.get(k); 

        String path = Environment.getExternalStorageDirectory().getAbsolutePath(); 
        File file = new File(path + File.separator + "Pictures" + File.separator + k + "_image.png"); 
        FileOutputStream ostream; 
        try { 
         file.createNewFile(); 
         ostream = new FileOutputStream(file); 
         m.compress(Bitmap.CompressFormat.PNG, 100, ostream); 
         ostream.flush(); 
         ostream.close(); 

         final Snackbar snackbar = Snackbar.make(frameLayout, "Note Saved", Snackbar.LENGTH_LONG); 
         snackbar.setAction("Close", new View.OnClickListener() { 
          @Override 
          public void onClick(View v) { 
           snackbar.dismiss(); 
          } 
         }); 
         snackbar.show(); 

        } catch (Exception e) { 
         e.printStackTrace(); 
         Log.w("Skoolify", e); 
        } 
        k = k + 1; 
       } 
      } catch (IndexOutOfBoundsException e) { 
       Log.w("Skoolify", "OutOFBonds"); 
      } 
      return true; 
     } else if (id == R.id.brush_menuitem) { 
      if (colorNsize.getVisibility() == View.VISIBLE) { 
       hideDrawer(colorNsize); 
      } else { 
       hideDrawer(eraserDrawer); 
       showDrawer(colorNsize); 
      } 

      return true; 
     } else if (id == R.id.eraser_menuitem) { 
      if (eraserDrawer.getVisibility() == View.VISIBLE) { 
       hideDrawer(eraserDrawer); 
      } else { 
       hideDrawer(colorNsize); 
       showDrawer(eraserDrawer); 
      } 

      return true; 
     } 

     else if(id==R.id.delete_menuitem){ 
      hideDrawer(colorNsize); 
      hideDrawer(eraserDrawer); 
      AlertDialog.Builder newDialog = new AlertDialog.Builder(this); 
      newDialog.setTitle("Discard the Notes"); 
      newDialog.setMessage("Do you want to discard the unsaved notes?"); 
      newDialog.setPositiveButton("Yes", new DialogInterface.OnClickListener() { 
       public void onClick(DialogInterface dialog, int which) { 
        NewNote.this.finish(); 

        dialog.dismiss(); 
       } 
      }); 
      newDialog.setNegativeButton("Cancel", new DialogInterface.OnClickListener() { 
       public void onClick(DialogInterface dialog, int which) { 
        dialog.cancel(); 
       } 
      }); 
      newDialog.show(); 

     } 

     return super.onOptionsItemSelected(item); 
    } 


    @Override 
    public void onClick(View v) { 
     if (v.getId() == R.id.small_brush) { 
      drawView.setBrushSize(smallBrush); 
      drawView.setLastBrushSize(smallBrush); 
      drawView.setErase(false); 
      hideDrawer(colorNsize); 
     } else if (v.getId() == R.id.medium_brush) { 
      drawView.setBrushSize(mediumBrush); 
      drawView.setLastBrushSize(mediumBrush); 
      drawView.setErase(false); 
      hideDrawer(colorNsize); 
     } else if (v.getId() == R.id.large_brush) { 
      drawView.setBrushSize(largeBrush); 
      drawView.setLastBrushSize(largeBrush); 
      drawView.setErase(false); 
      hideDrawer(colorNsize); 
     } else if (v.getId() == R.id.small_eraser) { 
      drawView.setErase(true); 
      drawView.setBrushSize(smallBrush); 
      hideDrawer(eraserDrawer); 
     } else if (v.getId() == R.id.medium_eraser) { 
      drawView.setErase(true); 
      drawView.setBrushSize(mediumBrush); 
      hideDrawer(eraserDrawer); 
     } else if (v.getId() == R.id.large_eraser) { 
      drawView.setErase(true); 
      drawView.setBrushSize(largeBrush); 
      hideDrawer(eraserDrawer); 
     } else if (v.getId() == R.id.previousbtn) { 
      hideDrawer(colorNsize); 
      hideDrawer(eraserDrawer); 
      try { 
       bitArrayStore(j); 
       drawView.startNew(); 
       j--; 
       if (bitmaps.size() > j) { 
        drawView.redraw(bitmaps, j); 
       } 
      } catch (IndexOutOfBoundsException e) { 
       j = 0; 
       try { 
        drawView.redraw(bitmaps, j); 
       }catch (IndexOutOfBoundsException e1){ 
        drawView.startNew(); 
       } 
      } 
      flag = false; 
     } else if (v.getId() == R.id.nextbtn) { 
      hideDrawer(colorNsize); 
      hideDrawer(eraserDrawer); 
      if (j < 50) { 
       bitArrayStore(j); 
       if (flag == false) { 
        j++; 
       } 
       if (bitmaps.size() > j) { 
        drawView.startNew(); 
        drawView.redraw(bitmaps, j); 
       } else { 
        drawView.startNew(); 
       } 
       flag = false; 
      } else { 
       Snackbar.make(v, "Reached page limit. Please save and start new note", Snackbar.LENGTH_LONG) 
         .setAction("Action", null).show(); 
      } 

     } 


    } 


    public void bitArrayStore(int k) { 

     if (drawView.canvasBitmap.sameAs(drawView.emptyBitmap)) { 
      flag = true; 
     } else { 

      try { 
       if (flag1 == false) { 
        drawView.buildDrawingCache(); 
        drawView.setDrawingCacheQuality(View.DRAWING_CACHE_QUALITY_HIGH); 
        bitmaps.set(k, Bitmap.createBitmap(drawView.getDrawingCache())); 

       } else { 
        bitmaps.add(k, Bitmap.createBitmap(drawView.getDrawingCache())); 
        flag1 = false; 
       } 
      } catch (IndexOutOfBoundsException e) { 
       bitmaps.add(k, Bitmap.createBitmap(drawView.getDrawingCache())); 

      } 
      drawView.destroyDrawingCache(); 

     } 
    } 

    public void redraww() 
    { 
     try{ 

      drawView.redraw(bitmaps, j); 
     }catch (IndexOutOfBoundsException e){ 
      drawView.startNew(); 
     } 

    } 
    public void hideDrawer(ViewGroup viewgrp) { 
     viewgrp.setVisibility(View.GONE); 
    } 

    public void showDrawer(ViewGroup viewgrp) { 
     viewgrp.setVisibility(View.VISIBLE); 
    } 

    @Override 
    protected void onSaveInstanceState(Bundle outState) { 
     super.onSaveInstanceState(outState); 
     bitArrayStore(j); 
     outState.putParcelableArrayList("Bits", bitmaps); 
     outState.putInt("j", j); 
     super.onSaveInstanceState(outState); 
    } 

    @Override 
    protected void onRestoreInstanceState(Bundle savedInstanceState) { 
     super.onRestoreInstanceState(savedInstanceState); 
     bitmaps=savedInstanceState.getParcelableArrayList("Bits"); 
     j = savedInstanceState.getInt("j"); 
     redraww(); 

    } 
} 

DrawingView.java

public class DrawingView extends View { 

    //drawing path 
    private Path drawPath; 
    //drawing and canvas paint 
    private Paint drawPaint, canvasPaint; 
    //initial color 
    private int paintColor = 0xFF0000c4; 
    //canvas 
    private Canvas drawCanvas; 
    //canvas bitmap 
    public Bitmap canvasBitmap, emptyBitmap; 
    private float brushSize, lastBrushSize; 
    private boolean erase = false; 


    public DrawingView(Context context, AttributeSet attrs) { 
     super(context, attrs); 
     setupDrawing(); 
    } 

    private void setupDrawing() { 
     brushSize = getResources().getInteger(R.integer.small_size); 
     lastBrushSize = brushSize; 
     drawPath = new Path(); 
     drawPaint = new Paint(); 
     drawPaint.setColor(paintColor); 
     drawPaint.setAntiAlias(true); 
     drawPaint.setStrokeWidth(20); 
     drawPaint.setStyle(Paint.Style.STROKE); 
     drawPaint.setStrokeJoin(Paint.Join.ROUND); 
     drawPaint.setStrokeCap(Paint.Cap.ROUND); 
     canvasPaint = new Paint(Paint.DITHER_FLAG); 
    } 

    protected void onSizeChanged(int w, int h, int oldw, int oldh) { 
//view given size 
     super.onSizeChanged(w, h, oldw, oldh); 
     canvasBitmap = Bitmap.createBitmap(w, h, Bitmap.Config.ARGB_8888); 
     drawCanvas = new Canvas(canvasBitmap); 
     emptyBitmap = Bitmap.createBitmap(canvasBitmap.getWidth(), canvasBitmap.getHeight(), canvasBitmap.getConfig()); 
    } 

    @Override 
    protected void onDraw(Canvas canvas) { 
//draw view 
     canvas.drawBitmap(canvasBitmap, 0, 0, canvasPaint); 
     canvas.drawPath(drawPath, drawPaint); 

    } 

    @Override 
    public boolean onTouchEvent(MotionEvent event) { 
//detect user touch 
     float touchX = event.getX(); 
     float touchY = event.getY(); 
     switch (event.getAction()) { 
      case MotionEvent.ACTION_DOWN: 
       drawPath.moveTo(touchX, touchY); 
       break; 
      case MotionEvent.ACTION_MOVE: 
       drawPath.lineTo(touchX, touchY); 
       break; 
      case MotionEvent.ACTION_UP: 
       drawCanvas.drawPath(drawPath, drawPaint); 
       drawPath.reset(); 
       break; 
      default: 
       return false; 
     } 
     invalidate(); 
     return true; 
    } 

    public void setColor(String newColor) { 
//set color 
     invalidate(); 
     paintColor = Color.parseColor(newColor); 
     drawPaint.setColor(paintColor); 
    } 

    public void setBrushSize(float newSize) { 
//update sizefloat pixelAmount = TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, 
     float pixelAmount = TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, 
       newSize, getResources().getDisplayMetrics()); 
     brushSize = pixelAmount; 
     drawPaint.setStrokeWidth(brushSize); 
    } 

    public void setLastBrushSize(float lastSize) { 
     lastBrushSize = lastSize; 
    } 

    public float getLastBrushSize() { 
     return lastBrushSize; 
    } 

    public void setErase(boolean isErase) { 
//set erase true or false 
     erase = isErase; 
     if (erase) drawPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.CLEAR)); 
     else drawPaint.setXfermode(null); 
    } 

    public void startNew() { 
     drawCanvas.drawColor(0, PorterDuff.Mode.CLEAR); 
     invalidate(); 


//  Bitmap b= BitmapFactory.decodeFile("/storage/emulated/0/Pictures/image.png"); 
//  drawCanvas.drawBitmap(b, 0, 0, null); 
// 
//  invalidate(); 

    } 


    public void redraw(ArrayList<Bitmap> bits, int i) { 
     try { 

       drawCanvas.drawBitmap(bits.get(i), 0, 0, canvasPaint); 
       invalidate(); 


     }catch (NullPointerException e){ 
      Log.w("DrawingApp","Exception"); 
     } 
    } 


} 

Answer 1

Эй, я нашел решение моей проблемы, с помощью Henry. Он указал, что перед инициализацией объектов я вызываю метод redraww(). Поэтому я решил проблему, вызвав свой метод в onWindowFocusChanged.

@Override 
    public void onWindowFocusChanged(boolean hasFocus) { 
     if (hasFocus) { 
      if (flag2 == true) { 
       redraww(); 
      } 
     } 
    } 

Я поставил flag2 так, чтобы оно не вызывать redraww() метод на первом создании деятельности.Он должен вызываться только тогда, когда есть saveInstanceState.

Answer 2

drawCanvas является недействительным в методе redraw(). Перед вызовом метода redraw() убедитесь, что вы создаете экземпляр drawCanvas.

Проводка полного кода поможет, где проблема.

Проблема в вашем onRestoreInstanceState(). Ваши объекты еще не инициализированы и до этого вы вызываете redraww. Я предлагаю вам удалить onRestoreInstanceState() и обработать его в onCreate(), чтобы избежать дублирования кода.

protected void onCreate(Bundle savedInstanceState){ 
     if(savedInstanceState != null){ 
      bitmaps=savedInstanceState.getParcelableArrayList("Bits"); 
      j = savedInstanceState.getInt("j"); 
    } 

    // go ahead with your object initialization. Once your `drawCanvas` is ready and initialized, then call `redraww`. 
} 

Answer 3

Переместить этот код в конструктор класса DrawingView.

//view given size 
     super.onSizeChanged(w, h, oldw, oldh); 
     canvasBitmap = Bitmap.createBitmap(w, h, Bitmap.Config.ARGB_8888); 
     drawCanvas = new Canvas(canvasBitmap); 
     emptyBitmap = Bitmap.createBitmap(canvasBitmap.getWidth(), canvasBitmap.getHeight(), canvasBitmap.getConfig());