How do I pass variables into a new android activity, with the ability to use them throughout the class?

Question

I'm trying to pass a variable into an activity, but I am getting a null object reference.

My intent declaration makes use of putExtra()

public void launch_test(View view) {
    playsound.start();
    Intent launch_test = new Intent(this, test.class);
        launch_test.putExtra("NUM_ROWS", 4);
        launch_test.putExtra("NUM_COLS", 4);
    startActivity(launch_test);
}

and my activity class (test) calls for the extras,

public class test extends Activity {
Intent launch_test = getIntent();
Bundle extras = launch_test.getExtras();

int NUM_ROWS = launch_test.getIntExtra("NUM_ROWS", 0);
int NUM_COLS = launch_test.getIntExtra("NUM_COLS", 0);

Button buttons[][] = new Button[NUM_ROWS][NUM_COLS];

etc...

but I'm getting a null object reference when I try to run it in an emulator.

I assume that I could use an IF statement to check for nulls, but Android Studio isn't letting me use the if statement in this area of the code. If I place the IF statement into the OnCreate function, than I won't be able to use the variables throughout the class, the way I would like to.

I'm very new at android coding, so I'm sorry if there's confusion!

Answer 1

如果您只想使用您的代码，请对其进行更正，请使用：extras.getIntExtra而不是launch_test.getIntExtra