如何调用MainActivity方法

Question

I'm trying to call method share() from a fragment. share() is in MainActivity.java

Button shareButton = new Button(getActivity());
shareButton.setOnClickListener(new View.onClickListener() {
   @Override
   public void onClick(View v) {
      MainActivity ma = new MainActivity();
      ma.share();              //Doesn't work! NullPointerException
   }
}

share():

public void share() {
     Intent i = new Intent();
     i.setAction(Intent.ACTION_SEND);
     i.setType("text/plain");
     i.putExtra(Intent.EXTRA_TEXT, shareString);
     startActivity(Intent.createChooser(i, "Say Something"));
}

Answer 1

Change

MainActivity ma = new MainActivity();

To

MainActivity ma = (MainActivity) getActivity();

getActivity() returns an instance of Activity so it must be cast

Answer 2

For example change this:

MainActivity ma = new MainActivity();

To this:

MainActivity ma = (MainActivity) getActivity();

Answer 3

（（MainActivity）getActivity（））。methodName这将帮助您，尝试一下

Answer 4

from software engineering Design principles

public class Utils {
    public static void share(Context context,String shareString) {
        Intent i = new Intent();
        i.setAction(Intent.ACTION_SEND);
        i.setType("text/plain");
        i.putExtra(Intent.EXTRA_TEXT, shareString);
        context.startActivity(Intent.createChooser(i, "#CrystalMaths"));

    }
}

and wherever you are use

Utils.share(getApplicationContext(),"share this line");

this makes our code reusable and cohesive