较旧的android版本上的android字符串数组nullpointerexception

Question

This code works fine on android 4.4, 5.0, 5.1 , 6.0

 File file = new File("/storage/emulated/0//Videos/");
    String[] myFiles;
    myFiles = file.list();
    for (int i = 0; i < myFiles.length; i++) {
        File myFile = new File(file, myFiles[i]);
        myFile.delete();
 }

But when i use this for android 4.0, 4.1, 4.2 i get java.lang.NullPointerException referring at line

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

So i try to initialize the String,

String[] myFiles = new String[100] //just big value

But android studio shows initializer "new String[100]" is redundent and error is not resolved.

Why does this happen?

Thanks..!

Answer 1

The javadoc for File.list() says that it can return null. You should always check for this whenever you call it and handle it correctly unless you are absolutely certain it will not return null.

Answer 2

This is because you are not checking your folder is null or not make sure your directory contains file

File file = new File("/storage/emulated/0//Videos/");
String[] myFiles;
if (file == null) {

} else {
    myFiles = file.list();
    for (int i = 0; i < myFiles.length; i++) {
        File myFile = new File(file, myFiles[i]);
         if(myFile.exists())
        myFile.delete();
    }
}

And if you want to delete whole directory than you can use this sample method

public void deleteDirectory(File file) {
if( file.exists() ) {
    if (file.isDirectory()) {
        File[] files = file.listFiles();
        for(int i=0; i<files.length; i++) {
            if(files[i].isDirectory()) {
                deleteDirectory(files[i]);
            }
            else {
                files[i].delete();
            }
        }
    }
        file.delete();
    }
}