Android: Save variables and settings on rotation

问题:

Is there a way to save variables that are being changed in the code, when the screen rotates? Thank you in advance

回答1:

You can save values into the instanceState Bundle when stopping an activity and restoring it when you start it. Like this:

@Override
protected void onRestoreInstanceState(Bundle savedInstanceState) {
    super.onRestoreInstanceState(savedInstanceState);
    // Read values from the "savedInstanceState"
}

@Override
protected void onSaveInstanceState(Bundle outState) {
    // Save the values you need into "outState"
    super.onSaveInstanceState(outState);
}

回答2:

Expanding on GSala's answer, this is sort of how I'd do it:

@Override
public void onSaveInstanceState(Bundle savedInstanceState){
    String someString = "this is a string";
    savedInstanceState.putString(CONSTANT_STRING, someString);
    //declare values before saving the state
    super.onSaveInstanceState(savedInstanceState);
}

Then in your onCreate you can get values like this:

@Override
    public void onCreate(final Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        addContentView(R.layout.view);

        //Make sure to do this check otherwise someString will
        //cause an error when your activity first loads!
        if (savedInstanceState != null){
            //Do whatever you need with the string here, like assign it to variable.
            Log.d("XXX", savedInstanceState.getString(STRING_CONSTANT));
        }
}

This way, you don't have to Override onRestoreInstanceState as well. Also, this can be done with just about any variable or object, not just strings.

See this documentation for more information.