java.lang.NullPointerException：尝试在空对象引用上调用虚拟方法 'char[] java.lang.String.toCharArray()'

Question

I am trying to read an image from the Android device then upload it to Microsoft Azure Mobile Service.

The pickImage() and onActivityResult() methods are working fine as image can be successfully display at the Image View by using the code

mImageView.setImageURI(currImageURI);

When I am trying to save the image by using the saveToDo() method there is an error at the line

FileInputStream fis = new FileInputStream(absoluteFilePath);

Therefore, I try to print out what exactly contains in the cursor by using the code

System.out.println("IMAGE: " + DatabaseUtils.dumpCursorToString(cursor));
System.out.println("CURRENT: " + DatabaseUtils.dumpCurrentRowToString(cursor));

I am getting the following error.

W/System.err: java.lang.NullPointerException: Attempt to invoke virtual method 'char[] java.lang.String.toCharArray()' on a null object reference
W/System.err:     at java.io.File.fixSlashes(File.java:183)
W/System.err:     at java.io.File.<init>(File.java:130)
W/System.err:     at java.io.FileInputStream.<init>(FileInputStream.java:103)

W/System.err:     at com.king.recipesharinghub.AddRecipe.saveTodo(AddRecipe.java:773)
W/System.err:     at com.king.recipesharinghub.AddRecipe$3.onClick(AddRecipe.java:214)

W/System.err:     at android.view.View.performClick(View.java:5198)
W/System.err:     at android.view.View$PerformClick.run(View.java:21147)
W/System.err:     at android.os.Handler.handleCallback(Handler.java:739)
W/System.err:     at android.os.Handler.dispatchMessage(Handler.java:95)
W/System.err:     at android.os.Looper.loop(Looper.java:148)
W/System.err:     at android.app.ActivityThread.main(ActivityThread.java:5417)
W/System.err:     at java.lang.reflect.Method.invoke(Native Method)
W/System.err:     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
W/System.err:     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
I/TodoDetailsActivity: JSON: {"complete":"false","text":"This is testing"}

These are the system outputs where the data is null.

I/System.out: Image URL: content://com.android.providers.media.documents/document/image%3A36
I/System.out: PROJECTION: [Ljava.lang.String;@290e1f6
I/System.out: DATABASE: >>>>> Dumping cursor android.content.ContentResolver$CursorWrapperInner@6cd59f7
I/System.out: 0 {
I/System.out:    _data=null
I/System.out: }
I/System.out: <<<<<
I/System.out: CURRENT: 0 {
I/System.out:    _data=null
I/System.out: }
I/System.out: INDEX: 0
I/System.out: ABSOLUTEFILEPATH: null

Below are the full codes

protected void pickImage() {
    Intent intent = new Intent(Intent.ACTION_GET_CONTENT);
    intent.setType("image/*");
    startActivityForResult(intent, 987);
}

@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
    super.onActivityResult(requestCode, resultCode, data);

    try {
        //handle result from gallary select
        if (requestCode == 987) {
            Uri currImageURI = data.getData();
            this.mImageUrl = currImageURI;
            //Set the image view's image by using imageUri
            mImageView.setImageURI(currImageURI);
        }
    } catch (Exception ex) {
        Log.e("TodoDetailsActivity", "Error in onActivityResult: " + ex.getMessage());
    }
}

protected void saveTodo() {
    String imageString = null;
    if (mImageUrl != null && !mImageUrl.equals("")) {
        try {
            System.out.println("Image URL: " + mImageUrl.toString());

            String[] projection = { MediaStore.Images.Media.DATA };
            System.out.println("PROJECTION: " + projection);

            Cursor cursor = getContentResolver().query(mImageUrl, projection,
                    null, null, null);
            cursor.moveToFirst();

            System.out.println("DATABASE: " + DatabaseUtils.dumpCursorToString(cursor));
            System.out.println("CURRENT: " + DatabaseUtils.dumpCurrentRowToString(cursor));

            int index = cursor
                    .getColumnIndex(MediaStore.Images.ImageColumns.DATA);

            System.out.println("INDEX: " + index);

            String absoluteFilePath = cursor.getString(index);

            System.out.println("ABSOLUTEFILEPATH: " + absoluteFilePath);

            FileInputStream fis = new FileInputStream(absoluteFilePath);

            int bytesRead = 0;
            ByteArrayOutputStream bos = new ByteArrayOutputStream();
            byte[] b = new byte[1024];
            while ((bytesRead = fis.read(b)) != -1) {
                bos.write(b, 0, bytesRead);
            }
            byte[] bytes = bos.toByteArray();
            imageString = Base64.encodeToString(bytes, Base64.DEFAULT);
        } catch (Exception ex) {
            ex.printStackTrace();
        }
    }
    new SaveTodoTask(this).execute("This is testing", imageString);
}

Hope to get my problem solve as I had stuck at this issue for several days. Thank you!

Answer 1

you should add projection in your code while calling the query,

     // Attempt to fetch asset filename for image
            String[] projection = { MediaStore.Images.Media.DATA };
photoCursor = context.getContentResolver().query( photoUri, 


                                projection, null, null, null );

then only you will be able to get

int index = cursor
                    .getColumnIndex(MediaStore.Images.ImageColumns.DATA);

Hope this will help you.

Answer 2

@luKing Saw, I tested your code in my simulator in Eclipse. Everything worked fine.

03-15 21:17:47.706: I/dalvikvm-heap(621): Grow heap (frag case) to 11.867MB for 1228816-byte allocation
03-15 21:17:49.296: I/System.out(621): Image URL: content://media/external/images/media/17
03-15 21:17:49.296: I/System.out(621): PROJECTION: [Ljava.lang.String;@414b3988
03-15 21:17:49.336: I/System.out(621): DATABASE: >>>>> Dumping cursor android.content.ContentResolver$CursorWrapperInner@414a9d50
03-15 21:17:49.336: I/System.out(621): 0 {
03-15 21:17:49.346: I/System.out(621):    _data=/mnt/sdcard/DCIM/Camera/IMG_20160315_171536.jpg
03-15 21:17:49.346: I/System.out(621): }
03-15 21:17:49.346: I/System.out(621): <<<<<
03-15 21:17:49.346: I/System.out(621): CURRENT: 0 {
03-15 21:17:49.346: I/System.out(621):    _data=/mnt/sdcard/DCIM/Camera/IMG_20160315_171536.jpg
03-15 21:17:49.356: I/System.out(621): }
03-15 21:17:49.356: I/System.out(621): INDEX: 0
03-15 21:17:49.356: I/System.out(621): ABSOLUTEFILEPATH: /mnt/sdcard/DCIM/Camera/IMG_20160315_171536.jpg
03-15 21:17:51.466: I/Choreographer(621): Skipped 562 frames!  The application may be doing too much work on its main thread.

I saw your Image Path like 'Content://com.android.providers.media.documents/document/image%3A36' ,but I am not sure your code can access into folder named 'document' in your project. Could you please try to use the image in SD card or src/res folder?