String[] array not working properly

Question

i have a Problem with String[] array.I refer about this from Here & Here

But still, i have not found any solution from the link.

What I want:

I am developing a Custom Camera App.I have a Folder in which I am saving a Captured images.also, i have 1 ImageView. when my App Launched the Image [or Bitmap] of Folder is set into that ImageView (Always set the First image of the folder into ImageView).

Following is my Code.

private void loadImageInImageView() {
        Uri[] mUrls;
        String[] mFiles = new String[0];

        File file = new File(android.os.Environment.getExternalStorageDirectory(), "CameraApp/Images");

        File[] imageList = file.listFiles(new FilenameFilter() {
            @Override
            public boolean accept(File file, String name) {
                return ((name.endsWith(".jpg")) || (name.endsWith(".png")) || (name.endsWith(".mp4")));
            }
        });

        if (mFiles.length >= 0) {
            Toast.makeText(this, "No Captured Images", Toast.LENGTH_SHORT).show();
        } else {
            mFiles = new String[imageList.length];

            for (int i = 0; i < imageList.length; i++) {
                mFiles[i] = imageList[i].getAbsolutePath();
            }
            mUrls = new Uri[mFiles.length];

            for (int i = 0; i < mFiles.length; i++) {
                mUrls[i] = Uri.parse(mFiles[i]);
                imgBtnThumbnail.setImageURI(mUrls[i]);
            }
        }
    }

in Above code [when Folder is Empty] :

When i set if (mFiles.length > 0)

it shows me an Error

Error: Attempt to get length of null array

When i set if (mFiles.length >= 0)

Then it shows me same as Above Error.
When i set if (mFiles == null)

it is also not Working because I have initialized String[] in above code.

String[] mFiles = new String[0]; Hence it also not work.

When I have some Images then it working Fine.because it executed the else part. what should I do?Whenever my Folder is Empty then it Shows me a Toast.otherwise my else code will be executed.

Any help will be Highly appreciated.

You are initializing mFiles array of size 0. String[] mFiles = new String[0] — d1vivek681065, Feb 03 '17 at 06:07
Yes...i did it bcz...i read about array initialization should start with 0. — Sagar Aghara, Feb 03 '17 at 06:09
^ :D. It's the size of array. If you initialize array with `new String[100]`, it will start from `0` and will end at `99`. — mallaudin, Feb 03 '17 at 06:11
`if (mFiles.length >= 0) {` - you're checking something strange. Length of an array is always non-negative. However, in this case it's even stranger because you check `mFiles`'s size, and `mFiles` had no way of changing after you've created it. I think you wanted to check `imageList.length == 0` — yeputons, Feb 03 '17 at 06:12
Just let it null . Check if null then show toast else do something with image — d1vivek681065, Feb 03 '17 at 06:13
tnx. all of you for Response..@yeputons..i am trying as you said. — Sagar Aghara, Feb 03 '17 at 06:14
why vote down...i tried more and more as i know...then after i post here..and sry for my English — Sagar Aghara, Feb 03 '17 at 06:18
who playing with this question.....sometimes vote up & sometimes vote down....stop this plz — Sagar Aghara, Feb 03 '17 at 07:22

score 2 · Answer 1 · answered Feb 03 '17 at 06:30

File[] imageList = file.listFiles(new FilenameFilter() {
        @Override
        public boolean accept(File file, String name) {
            return ((name.endsWith(".jpg")) || (name.endsWith(".png")) || (name.endsWith(".mp4")));
        }
    });

if (imageList.length = 0) {
        Toast.makeText(this, "No Captured Images", Toast.LENGTH_SHORT).show();
    } else {
        String[] mFiles = new String[imageList.length];

        for (int i = 0; i < imageList.length; i++) {
            mFiles[i] = imageList[i].getAbsolutePath();
        }
        mUrls = new Uri[mFiles.length];

        for (int i = 0; i < mFiles.length; i++) {
            mUrls[i] = Uri.parse(mFiles[i]);
            imgBtnThumbnail.setImageURI(mUrls[i]);
        }
    }

here what i use.....if (imageList.length = 0)...i think here == .in if() — Sagar Aghara, Feb 03 '17 at 06:38
@faranjit..Thanks Man also your Answer is working Properly....but i can not marked 2 Question..thats why vote up. — Sagar Aghara, Feb 03 '17 at 06:45

Ethan Choi · Accepted Answer · 2017-02-03T07:31:31.423

1

If the function you want works when the size of the imageList is greater than zero, try below code.

private void loadImageInImageView() {

    File file = new File(android.os.Environment.getExternalStorageDirectory(), "CameraApp/Images");

    File[] imageList = file.listFiles(new FilenameFilter() {
        @Override
        public boolean accept(File file, String name) {
            return ((name.endsWith(".jpg")) || (name.endsWith(".png")) || (name.endsWith(".mp4")));
        }
    });

    // conditional operator [ ? : ]
    // value = (experssion) ? value if true : value if false
    // ref : https://www.tutorialspoint.com/java/java_basic_operators.htm
    int imgLength = imageList == null ? 0 : imageList.length;

    if(imgLength > 0)
    {
        String[] mFiles =  new String[imgLength];
        Uri[] mUrls = new Uri[imgLength];

        //merge for condition
        for (int i = 0; i < imgLength; i++) {
            mFiles[i] = imageList[i].getAbsolutePath();
            mUrls[i] = Uri.parse(mFiles[i]);
            imgBtnThumbnail.setImageURI(mUrls[i]);
        }
    }
    else
    {
        Toast.makeText(this, "No Captured Images", Toast.LENGTH_SHORT).show();
    }
}

edited Feb 03 '17 at 07:31

answered Feb 03 '17 at 06:27

Ethan Choi

2,339
18
28

Ethan Choi....your answer is very very Cool and works very Fine...like a works Like a Charm...thanks You saved my Time. – Sagar Aghara Feb 03 '17 at 06:42
can you tell me the meaning of this Line..... int imgLength = imageList == null ? 0 : imageList.length; – Sagar Aghara Feb 03 '17 at 06:58
and what if i used single for() condition.instead of 2 for() condition...because of both are same..? – Sagar Aghara Feb 03 '17 at 07:01
int imgLength = imageList == null ? 0 : imageList.length is meaning if imageList is null then imgLength is zero else image.length – Ethan Choi Feb 03 '17 at 07:22
then i can put the both condition code into single one..? – Sagar Aghara Feb 03 '17 at 07:24
Thanks man...can you give me tutorial or material link or just tell me what we say this Line........int imgLength = imageList == null ? 0 : imageList.length;...........i understood bcz you told me...but i want to know deeply. – Sagar Aghara Feb 03 '17 at 07:27
Thank you very very..much.i will check about conditional operator. – Sagar Aghara Feb 03 '17 at 07:29

Kiran Benny Joseph · Answer 3 · 2017-02-03T06:38:30.920

0

private void loadImageInImageView() {
        Uri[] mUrls;
        File[] imageList

        File file = new File(android.os.Environment.getExternalStorageDirectory(), "CameraApp/Images");

        imageList = file.listFiles(new FilenameFilter() {
            @Override
            public boolean accept(File file, String name) {
                return ((name.endsWith(".jpg")) || (name.endsWith(".png")) || (name.endsWith(".mp4")));
            }
        });

        if (imagelist==null && imageList.length == 0) {
            Toast.makeText(this, "No Captured Images", Toast.LENGTH_SHORT).show();
        } else {

            for (int i = 0; i < imageList.length; i++) {

                imgBtnThumbnail.setImageURI(Uri.parse(imageList[i].getAbsolutePath()););
            }
        }
    }

try this; but your image changes continuously because of for loop;

edited Feb 03 '17 at 06:38

answered Feb 03 '17 at 06:16

Kiran Benny Joseph

6,755
4
38
57

java.lang.RuntimeException: Unable to start activity ComponentInfo{com.devkrushna.camerademo/com.devkrushna.camerademo.MainActivity}: java.lang.NullPointerException: Attempt to get length of null array.............shown me error – Sagar Aghara Feb 03 '17 at 06:23
Probably your `imageList ` is null – Paresh P. Feb 03 '17 at 06:27
check it. I have edittedt it. but your imagelist is null @Sagar Aghara – Kiran Benny Joseph Feb 03 '17 at 06:40

score 0 · Answer 4 · answered Feb 03 '17 at 06:22

0

Do not initialize mFiles. Initialize it in the moment when you add some data. And for checking if it isn't empty use this:

if (mFiles != null && mFiles.length > 0) {
    ...
}

answered Feb 03 '17 at 06:22

reaven

91
4

@reaven...i did as you say.....but when i am not initialize mFiles..Android Studio given me Red Line above mFiles....and said Variable mFiles might not have been initialized. – Sagar Aghara Feb 03 '17 at 06:28
So initialize it with null first: String[] mFiles = null; It won't show red line that way. – reaven Feb 03 '17 at 06:42

String[] array not working properly

4 Answers4