在Android Studio中警告NullPointerException

Question

When i do:

SharedPreferences logData = PreferenceManager.getDefaultSharedPreferences(this);

if(logData.getString("myString", null).equals("some_value")) {

    // do some stuff…

} else {

    // do some other…
}

Android Studio warnings me that:

Method invocation 'logData.getString("myString", null).equals("some_value")' may produce ' java.lang.NullPointerException'

How can I avoid this warning? Thanks.

Answer 1

The method getString() will throw NUllPointerExcception because you are returning default null value by passing second parameters.

There are two ways to avoid this,

First, by passing empty string as default value as second argument in getString()

SharedPreferences logData = PreferenceManager.getDefaultSharedPreferences(this);

if(logData.getString("myString", "").equals("some_value")) 

or Second,

First get your String in reference variable than check it for null or not like,

String logDataString = logData.getString("myString", null);
if(logDataString  != null && logDataString.equals("some_value"))

Answer 2

You can't call equals method on a null object. Try to get the String first and check if it is null.

String myString = PreferenceManager.getDefaultSharedPreferences(
    getBaseContext()).getString("myString", null);

if (myString != null) {
    if (myString.equals("something")) {

    }
    else {

    }
}

Or changing the default value returned by getString method

if (!PreferenceManager.getDefaultSharedPreferences(
    getBaseContext()).getString("myString", "").equals("")) {

}