由于某种原因，我的if语句没有触发

Question

I have created an onSharedPreferencesChangeListener which is working correctly. I know this because when I setup the listener I logged the listener and it is triggering on a change.

However, I was getting an error when I was trying to switch the key variable (saying that I need JRE 1.7+ in order to switch a string), so I changed it to if-elseif statements.

The if-elseif statements weren't triggering so I changed the first two to if statements and put the elseif after that (thinking that the elseif might have been the problem). Still no triggering.

The weird thing is that when I logged the event trigger, I output " "+key+" " as the string and the key value is the exact strings that I'm testing for.

Here is my code, can someone point me in the right direction please?

    // logic for action when a shared preference is changed.
    prefs.registerOnSharedPreferenceChangeListener( new SharedPreferences.OnSharedPreferenceChangeListener() {

        @Override
        public void onSharedPreferenceChanged(SharedPreferences sharedPreferences, String key) {
            String TAG = "UltimateScoreboard";

            if (key == "Main_Clock_Minutes") {
                msMainClockStart = Long.valueOf( prefs.getString( "Main_Clock_Minutes", "0" ) ) * 60000;
                Log.i( TAG, key + " changed: " + String.valueOf(msMainClockStart) );
            }

            if ( key == "Use_ShotClock" ) {
                useShotClock = prefs.getBoolean( "Use_ShotClock", false );

                if( useShotClock )
                    btnShotClock.setVisibility( View.VISIBLE );
                else
                    btnShotClock.setVisibility( View.INVISIBLE );

                Log.i( TAG, key );
            } 

            else if ( key == "Shot_Clock_Seconds" ) {
                msShotClockStart = Long.valueOf( prefs.getString( "Shot_Clock_Seconds", "0" ) ) * 1000;
                Log.i( TAG, key + " changed: " + Long.valueOf(msShotClockStart) );
            }

Answer 1

You must use the String.equals() function to compare strings. == with Strings only compares memory locations.

For example: if (key.equals("Main_Clock_Minutes"))

Answer 2

You can not compare strings using == . Use the String class methods equals() or equalsIgnoreCase() .

if ( key.equals("Use_ShotClock") ) { }

This is how you compare strings

Answer 3

you should compare like if ( key.equals("Use_ShotClock")) or if ( key.equalsIgnoreCase("Use_ShotClock")). because string are objects in java. so if you compare like if ( key == "Use_ShotClock" ) it will try to compare the referances of those 2 string objects which will be different.

Answer 4

Have you tried using .equals() in comparing strings ?

Like this:

if (key.equals("Main_Clock_Minutes")) {
    msMainClockStart = Long.valueOf( prefs.getString( "Main_Clock_Minutes", "0" ) ) * 60000;
    Log.i( TAG, key + " changed: " + String.valueOf(msMainClockStart) );
} else if ( key.equals("Use_ShotClock")) {
    useShotClock = prefs.getBoolean( "Use_ShotClock", false );

    if( useShotClock )
        btnShotClock.setVisibility( View.VISIBLE );
    else
        btnShotClock.setVisibility( View.INVISIBLE );

    Log.i( TAG, key );
} else if ( key.equals("Shot_Clock_Seconds")) {
    msShotClockStart = Long.valueOf( prefs.getString( "Shot_Clock_Seconds", "0" ) ) * 1000;
    Log.i( TAG, key + " changed: " + Long.valueOf(msShotClockStart) );
}

Answer 5

Strings have to be tested on equality with String's method equals(String s).

The "==" Operator hasn't been overloaded for Strings and because a String is a reference Type (it's an object, not a primitive type) it's the memory address which is compared using "==". Because of Javas ability to share memory for multiple variables, there is a chance to get true when comparing strings with "==", but that's less probable and very unpredictable.