如何开始一个新活动并在该活动中启动方法

Question

So I'm working with Java in android studio and I want to start a new class from a different class (I'm in ListenerServiceFromWear and want to start MainActivity ) and once Mainactivity is started I want to start a method ( startEmergencyMode(); ) in Mainactivity .

How do I do this from ListenerServiceFromWear ?

Answer 1

Start MainActivity with an intent and in the extra of the intent put some flag that will tell MainActivity to call startMergencyMode()

Intent intent = new Intent(this, Mainactivity.class);
intent.putExtra("isEmergency", true);
startActivity(intent);

And then in Mainactivity actually call startEmergencyMode()

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    // ...

    Intent intent = getIntent();
    boolean isEmergency = intent.getBooleanExtra("isEmergency", false);

    if(isEmergency){
        startEmergencyMode();
    }
}

Answer 2

I don't quite understand what you mean by "start"

In java, you either:

• Declare a static field or method
• Create an instance of an object and use its public fields and methods.

If you wish to just have one 'instance' of MainActivity , use a static method:

public static void startEmergencyMode() {
    // Code here
}

Which you can call anywhere using MainActivity.startEmergencyMode() . Keep in mind that this static method can only access static fields and other static methods.

If you wish to create an instance of MainActivity , simply create one and call the method:

public void startEmergencyMode() {
    // Code here
}


// Somewhere else
MainActivity activity = new MainActivity();
activity.startEmergencyMode();

If you don't understand the difference between a static and non static method or field, refer the answer on this thread: What does 'public static void' mean in Java?