9

I would like to log raw data like arrays in my logcat, so I know what is the output. Lets say I have an array... like that:

File[] mp3List = ...
Log.v("test", mp3List);

Why can't I just log the array to console? How can I do it?

Badr Hari
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5 Answers5

14

You can't log the array because it is just an Object. LogCat has no idea how to deal with it or display it in a way you want.

If each File object has a toString() method that displays the information that you want you can use:

Log.v(Arrays.toString(mp3List));

Otherwise you'll have to concatenate your own String to log:

StringBuilder sb = new StringBuilder();
for(File f : mp3List) {
  sb.append(f.getName());
}

Log.v(sb.toString());
Jivings
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10

The reason why this doesn't work is simply because the 2nd argument of Log.v is a String not a File[]. Java strictly enforces argument types.

Update:

You can easily transform the information contained a File object into a String object. All java objects implement a toString(), which if I remember correctly returns a combination of the ClassName and the address of the object is located. However this usually doesn't contain useful information. So you need to define the conversion yourself.

Now to convert from File[] to String is more complicated because you when call a method on an array it works on the array object rather than on members of an array (which contains the information I suspect you care about). So calling mp3List.toString() will return a single string that describes the array object and not the information contained in the array.

So you'll probably want to write a method like this:

String fileArrayToString(File[] f){
    String output = "";
    String delimiter = "\n" // Can be new line \n tab \t etc...
    for (int i=0; i<f.length; i++)
    {
        output = output + f[i].getPath() + delimiter;
    }

    return output;
}

And then call make your log call as follows:

Log.v("MyTag", fileArraytoString(mp3List);

However this might be hard to read.

I personally would do it like this:

for (int i=0; i<mp3List.legnth; i++)
    Log.v("MyTag", Integer.toString(i) + ":" + mp3List[i].getPath());

Its simpler, produces cleaner log messages and is easier to understand what is going on as a programmer.

slayton
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1

If you have a String array, you can just add toString() to it and it will be displayed.

For custom objects, you should override the toString() method and print what you want to see for that object. If you then have an array, the array will be printed with the output from the toString method.

J. Maes
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  • If I use toString, it will log something like: "Ljava.io.File;@4052eac0" which doesn't really help me at all. – Badr Hari Jan 30 '12 at 18:18
  • That's why you should override the toString method in your class of which you want to print the information. – J. Maes Jan 31 '12 at 07:56
0

I like one liners better:

for(File file:list) Log.d(TAG, "list: " + file.getPath());

albertpeiro
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0

Maybe I misunderstood, but I think its simply:

string sLog = "";
for(mp3List..)
{
    sLog += mp3List[i].getName();
}

Log.v(sLog);

isnT it? Because, I suppose, when you try to print an array like that you ll get a log entry saying that mp3List is an System.Blah.Blah.File[] ..

Hope it helps..

Orkun
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    String concatenation should be done using a StringBuilder. Using += creates a new String Object for each iteration because Strings are immutable. – Jivings Jan 30 '12 at 18:20