关于异常：NullPointerException：尝试调用虚方法’int android.graphics.Bitmap.getWidth()’

NullPointerException: Attempt to invoke virtual method 'int android.graphics.Bitmap.getWidth()'

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public class CategoryAdapter extends BaseAdapter {
Context context;
ArrayList<ModelCategory> model;
LayoutInflater layoutInflater;

public CategoryAdapter(Activity activity, ArrayList<ModelCategory> model) {
this.model = model;
this.context = activity;
}

@Override
public int getCount() {
return model.size();
}

@Override
public Object getItem(int position) {
return null;
}

@Override
public long getItemId(int position) {
return position;
}

@Override
public View getView(int position, View convertView, ViewGroup parent) {

ViewHolder viewHolder = null;
layoutInflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
if (convertView == null) {
viewHolder = new ViewHolder();
convertView = layoutInflater.inflate(R.layout.category_adapter, parent, false);
viewHolder.imageView = (ImageView) convertView.findViewById(R.id.category_grid_image);
viewHolder.textView = (TextView) convertView.findViewById(R.id.get_category_title);
convertView.setTag(viewHolder);

} else {
viewHolder = (ViewHolder) convertView.getTag();
}

viewHolder.textView.setText(model.get(position).getCategoryName());
if(position<=3){
viewHolder.imageView.setImageBitmap(StringToBitMap(model.get(position).getCategoryImage()));
}
else {
viewHolder.imageView.setImageBitmap(getBitmap(model.get(position).getCategoryImage()));
}
return convertView;
}

private class ViewHolder {
public ImageView imageView;
public TextView textView;
}

private Bitmap getBitmap(String path) {

BitmapFactory.Options option = new BitmapFactory.Options();
option.inSampleSize = 8;
Bitmap bitmap = BitmapFactory.decodeFile(path, option);
Matrix matrix = new Matrix();
matrix.postRotate(getImageOrientation(path));
Bitmap rotatedBitmap = Bitmap.createBitmap(bitmap, 0, 0, bitmap.getWidth(), bitmap.getHeight(), matrix, true);
Bitmap resized = Bitmap.createScaledBitmap(rotatedBitmap, 150, 150, true);
return resized;
}

private static int getImageOrientation(String imagePath) {
int rotate = 0;
try {
File imageFile = new File(imagePath);
ExifInterface exif = new ExifInterface(
imageFile.getAbsolutePath());
int orientation = exif.getAttributeInt(
ExifInterface.TAG_ORIENTATION,
ExifInterface.ORIENTATION_NORMAL);

switch (orientation) {
case ExifInterface.ORIENTATION_ROTATE_270:
rotate = 270;
break;
case ExifInterface.ORIENTATION_ROTATE_180:
rotate = 180;
break;
case ExifInterface.ORIENTATION_ROTATE_90:
rotate = 90;
break;
}
} catch (IOException e) {
e.printStackTrace();
}

return rotate;
}

public Bitmap StringToBitMap(String encodedString){
try {
byte [] encodeByte=Base64.decode(encodedString, Base64.DEFAULT);
Bitmap bitmap=BitmapFactory.decodeByteArray(encodeByte, 0, encodeByte.length);
return bitmap;
} catch(Exception e) {
e.getMessage();
return null;
}
}

}

我得到error如下

java.lang.NullPointerException: Attempt to invoke virtual method 'int
android.graphics.Bitmap.getWidth()' on a null object reference
at com.adapter.CategoryAdapter.getBitmap(CategoryAdapter.java:92)
at com.adapter.CategoryAdapter.getView(CategoryAdapter.java:75)
at android.widget.AbsListView.obtainView(AbsListView.java:2896)
at android.widget.GridView.makeAndAddView(GridView.java:1456)
at android.widget.GridView.makeRow(GridView.java:361)
at android.widget.GridView.fillDown(GridView.java:302)
at android.widget.GridView.fillFromTop(GridView.java:437)
at android.widget.GridView.layoutChildren(GridView.java:1284)
at android.widget.AbsListView.onLayout(AbsListView.java:2700)
at android.view.View.layout(View.java:16899)
at android.view.ViewGroup.layout(ViewGroup.java:5405)
at android.widget.RelativeLayout.onLayout(RelativeLayout.java:1077)
at android.view.View.layout(View.java:16899)
at android.view.ViewGroup.layout(ViewGroup.java:5405)
at android.widget.FrameLayout.layoutChildren(FrameLayout.java:579)
at android.widget.FrameLayout.onLayout(FrameLayout.java:514)
at android.view.View.layout(View.java:16899)
at android.view.ViewGroup.layout(ViewGroup.java:5405)
at android.support.v4.widget.DrawerLayout.onLayout(DrawerLayout.java:1043)
at android.view.View.layout(View.java:16899)
at android.view.ViewGroup.layout(ViewGroup.java:5405)
at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1702)
at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1556)
at android.widget.LinearLayout.onLayout(LinearLayout.java:1465)
at android.view.View.layout(View.java:16899)
at android.view.ViewGroup.layout(ViewGroup.java:5405)
at android.widget.RelativeLayout.onLayout(RelativeLayout.java:1077)
at android.view.View.layout(View.java:16899)
at android.view.ViewGroup.layout(ViewGroup.java:5405)
at android.widget.FrameLayout.layoutChildren(FrameLayout.java:579)
at android.widget.FrameLayout.onLayout(FrameLayout.java:514)
at android.view.View.layout(View.java:16899)
at android.view.ViewGroup.layout(ViewGroup.java:5405)
at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1702)
at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1556)
at android.widget.LinearLayout.onLayout(LinearLayout.java:1465)
at android.view.View.layout(View.java:16899)
at android.view.ViewGroup.layout(ViewGroup.java:5405)
at android.widget.FrameLayout.layoutChildren(FrameLayout.java:579)
at android.widget.FrameLayout.onLayout(FrameLayout.java:514)
at android.view.View.layout(View.java:16899)
at android.view.ViewGroup.layout(ViewGroup.java:5405)
at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1702)
at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1556)
at android.widget.LinearLayout.onLayout(LinearLayout.java:1465)
at android.view.View.layout(View.java:16899)
at android.view.ViewGroup.layout(ViewGroup.java:5405)
at android.widget.FrameLayout.layoutChildren(FrameLayout.java:579)
at android.widget.FrameLayout.onLayout(FrameLayout.java:514)
at android.view.View.layout(View.java:16899)
at android.view.ViewGroup.layout(ViewGroup.java:5405)

我怎么解决这个问题？