如何过滤SharedPreferences导入ArrayList中的空值？求正确代码

Hey there! I totally get how annoying it is when those unwanted empty or null values pop up in your ArrayList even after you tried adding checks. Let’s break down why your previous attempts might’ve failed and give you solid, working code to fix this.

Common Reasons Your Checks Didn’t Work #

Chances are, you were only checking for null but not accounting for empty strings (or strings with just spaces). SharedPreferences can return empty strings if you set a default value like "" when using getString(), and those won’t trigger a null check.

Solution 1: Filter Values While Reading from SharedPreferences #

This is the cleanest approach—we filter out bad values as we pull them from SharedPreferences instead of cleaning up later.

Case 1: Reading all key-value pairs

If you’re fetching all entries from SharedPreferences:

// Get your SharedPreferences instance
SharedPreferences prefs = getSharedPreferences("YourPrefsFile", MODE_PRIVATE);
Map<String, ?> allEntries = prefs.getAll();
ArrayList<String> filteredList = new ArrayList<>();

for (Map.Entry<String, ?> entry : allEntries.entrySet()) {
    Object value = entry.getValue();
    // Skip null values, and strings that are empty or just whitespace
    if (value != null) {
        String strValue = value.toString();
        if (!strValue.trim().isEmpty()) {
            filteredList.add(strValue);
        }
    }
}

// Now filteredList is ready to display—no empty/null items!

Case 2: Reading specific known keys

If you have a list of keys you need to fetch:

SharedPreferences prefs = getSharedPreferences("YourPrefsFile", MODE_PRIVATE);
// Replace with your actual keys
String[] targetKeys = {"username", "email", "favoriteColor"};
ArrayList<String> filteredList = new ArrayList<>();

for (String key : targetKeys) {
    // Set default value to null instead of "" so we can detect missing keys
    String value = prefs.getString(key, null);
    // Check for both null AND empty/whitespace-only strings
    if (value != null && !value.trim().isEmpty()) {
        filteredList.add(value);
    }
}

Solution 2: Clean Up an Existing ArrayList #

If you already have an ArrayList that’s been populated (and has unwanted empty values), use an Iterator to safely remove bad entries (this avoids ConcurrentModificationException):

ArrayList<String> originalList = ...; // Your existing list with empty/null items
Iterator<String> iterator = originalList.iterator();

while (iterator.hasNext()) {
    String item = iterator.next();
    // Remove nulls, empty strings, and strings with only spaces
    if (item == null || item.trim().isEmpty()) {
        iterator.remove();
    }
}

// originalList now has no unwanted entries

Key Takeaways #

• Always set the default value to null when using getString()—this lets you tell the difference between a missing key and an intentionally empty value.
• Don’t forget to check for whitespace-only strings with trim().isEmpty()—they look empty but won’t be caught by a simple !value.isEmpty().
• Use an Iterator when removing items from a list during iteration to avoid errors.

内容的提问来源于stack exchange，提问作者Nouran Katana