1.Activity

public class MainActivity extends AppCompatActivity {
    @Override
protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
FragmentTransaction far=getSupportFragmentManager().beginTransaction();
Farment fa=new 
 
Farment();
far.add(R.id.far,fa,Farment.class.getName());
far.commit();
setView();
}
    private void setView() {
        final Button button= (Button) findViewById(R.id.button01);
button.setOnClickListener(new View.OnClickListener() {
            @Override
public void onClick(View v) {
                Button a= (Button) getSupportFragmentManager().findFragmentById(R.id.far
 
).getView().findViewById(R.id.button);
a.setText("789");
}
        });
}

2.碎片

public class Farment extends Fragment {
    View view;
Button button;
@Nullable
    @Override
public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        view 
 
= inflater.inflate(R.layout.far_main, null);
setview(view);
        return view;
}
    public void setview(View view) {
        this.view = view;
button = (Button) view.findViewById(R.id.button);
button.setText("hahah");
}