我不能在我的活动中调用我的片段方法，我想在两个不同的片段中调用两个方法？

Question

public class MainActivity extends FragmentActivity {
    ViewPager viewpager;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        viewpager = (ViewPager)findViewById(R.id.viewPager);
        MyFragmentAdapter adapter = new MyFragmentAdapter(getSupportFragmentManager());
        viewpager.setAdapter(adapter);
    }

    private class MyFragmentAdapter extends FragmentPagerAdapter{

        public MyFragmentAdapter(FragmentManager fm) {
            super(fm);
            // TODO Auto-generated constructor stub
        }

        @Override
        public Fragment getItem(int position) {
            // TODO Auto-generated method stub
            switch (position) {
            case 0:
                return new WeatherCurrentFragment();
            case 1:
                return new WeatherForeCastFragment();
            }
            return null;
        }

        @Override
        public int getCount() {
            // TODO Auto-generated method stub
            return 2;
        }

    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.weather, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        if(item.getItemId() == R.id.change_city){
            showInputDialog();
        }
        return super.onOptionsItemSelected(item);
    }

    private void showInputDialog(){
        AlertDialog.Builder builder = new AlertDialog.Builder(this);
        builder.setTitle("Change city");
        final EditText input = new EditText(this);
        input.setInputType(InputType.TYPE_CLASS_TEXT);
        builder.setView(input);
        builder.setPositiveButton("Go", new DialogInterface.OnClickListener() {
            @Override
            public void onClick(DialogInterface dialog, int which) {
                changeCity(input.getText().toString());
            }
        });
        builder.show();
    }

    public void changeCity(String city){
         WeatherCurrentFragment cf = (WeatherCurrentFragment)getSupportFragmentManager().findFragmentById(R.id.currentweather);
         cf.updateWeatherData(city);
         WeatherForeCastFragment ff = (WeatherForeCastFragmen)getSupportFragmentManager().findFragmentById(R.id.forecast);
         ff.updateWeatherData(city);
         new CityPreference(this).setCity(city);
    }
}

并且显示错误

07-18 08:59:34.755: E/AndroidRuntime(2114): java.lang.NullPointerException: Attempt to invoke virtual method 'void example.giaodien1.WeatherCurrentFragment.updateWeatherData(java.lang.String)' on a null object reference

正如您所看到的，当我单击Button时，我想从CurrentWeatherFragment调用一个方法，从ForecastWeatherFragment调用一个方法。

Answer 1

代码如下：

getSupportFragmentManager().findFragmentById(R.id.currentweather);

返回空对象引用。

这个问题可能对您有帮助，findFragmentById返回null

public interface OnCityChangedListener(){
    public void onCityChanged(String city);
}

public MyFragment extends Fragment implements OnCityChangedListener

@override
public void onCityChanged(String city){
    updateWeatherData(city);
}

public MyFragmentAdapter(FragmentManager fm, ArrayList<Fragment> fs) {
    super(fm);
    this.fs = fs;
}

public void changeCity(String city){
    fs.onCityChanged(city);
}