java - android 未知的空指针错误

Question

这个问题已经有答案了:

What is a NullPointerException, and how do I fix it? (12 个回答)

已关闭 6 年前。

我需要在alertdialog中显示gridview...当我使用此代码时，我收到此错误...

java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.Object android.app.Activity.getSystemService(java.lang.String)' on a null object reference

我的maincode ....

 GridView grid;
GridViewAdapter adapter1;
 listView_prev.setOnItemClickListener(new AdapterView.OnItemClickListener() {
        @Override
        public void onItemClick(AdapterView<?> arg0, final View arg1, int arg2, long arg3) {
            //listview click event handling
           TextView id = (TextView) arg1.findViewById(R.id.textView17);
            final int id_To_Search = Integer.valueOf(id.getText().toString());
            Cursor item=mydb.singlecons(id_To_Search);
            Cursor att=mydb.attrs(id_To_Search);
            Cursor picloc=mydb.singleconspic(id_To_Search);
            att.moveToFirst();
            List<String> list = new ArrayList<>();
          //  Log.d("temp",att.getColumnName(1));

            while (!att.isAfterLast())
            {
                int l=att.getColumnCount();
                Log.d("length", String.valueOf(l));
                for(int i=2;i<l;i++){
                Log.d("for","for");
                    if(att.getString(i)!=null){
                        String b= att.getColumnName(i)+" "+att.getString(i);
                        list.add(b);
                        Log.d("att",b);
                    }
                }
                Log.d("while","while");
                att.moveToNext();
            }
            att.close();
            Log.d("list", String.valueOf(list));
            picloc.moveToFirst();

            FilePathStrings = new String[picloc.getCount()];
            int i=0;
            while (!picloc.isAfterLast()){
                Log.d("picloc",picloc.getString(2));
                FilePathStrings[i]=picloc.getString(2);
                i++;
                picloc.moveToNext();
            }

            item.moveToFirst();

            AlertDialog.Builder dialogBuilder = new AlertDialog.Builder(Consultation.this);
            LayoutInflater inflater = getLayoutInflater();
            View dialogView = inflater.inflate(R.layout.alert_label_editor, null);
            dialogBuilder.setView(dialogView);

            TextView con=(TextView)dialogView.findViewById(R.id.textView29);
            con.setText("Consultation on "+item.getString(4));
            TextView des=(TextView)dialogView.findViewById(R.id.textView28);
            des.setText(item.getString(2));
            TextView pre=(TextView)dialogView.findViewById(R.id.textView31);
            pre.setText(item.getString(3));
            TextView fee=(TextView)dialogView.findViewById(R.id.textView32);
            fee.setText(item.getString(5));
            adapter1 = new GridViewAdapter(FilePathStrings);

            grid.setAdapter(adapter1);
            AlertDialog alertDialog = dialogBuilder.create();
            alertDialog.show();


        }
    });

Gridviewadapter类...

class GridViewAdapter extends BaseAdapter {

private Activity activity;
private String[] filepath;
private static LayoutInflater inflater = null;
GridViewAdapter(String[] fpath) { //you need to pass Activity reference here
    filepath = fpath;
    activity = activity;
    inflater = (LayoutInflater) activity
            .getSystemService(Context.LAYOUT_INFLATER_SERVICE);
}
public int getCount() {
    return filepath.length;

}

public Object getItem(int position) {
    return position;
}

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

public View getView(int position, View convertView, ViewGroup parent) {
    View vi = convertView;
    if (convertView == null)
        vi = inflater.inflate(R.layout.gridview_item, null);
        ImageView image = (ImageView) vi.findViewById(R.id.image);
        Bitmap bmp = BitmapFactory.decodeFile(filepath[position]);
        image.setImageBitmap(bmp);
        return vi;
}

}

我该如何解决这个问题？我需要用警报对话框显示图像...我怎样才能解决这个问题...

Answer 1

实际上你的上下文是空的，所以像这样改变

GridViewAdapter(String[] fpath,Context context) { 
 filepath = fpath;
 inflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);

}

像这样在您的 Activity 类中调用 GridViewAdapter

adapter1 = new GridViewAdapter(FilePathStrings,getApllicationContext());