从活动中调用片段方法的问题

Question

I have issues with fragment method called form activity. For creating the fragment and calling the method I use this method situated in MainActivity.java:

public void createFragment (int select, String string) {
    switch (select) {
        case 1:
            ErrorFragment errorFragment = new ErrorFragment();
            getSupportFragmentManager().beginTransaction()
                    .replace(R.id.fragError, errorFragment)
                    .commit();

            errorFragment = (ErrorFragment) getSupportFragmentManager().findFragmentById(R.id.fragError);

            errorFragment.setText(string);

            break;
        case 2:
            StringFragment stringFragment = new StringFragment();
            getSupportFragmentManager().beginTransaction()
                    .replace(R.id.fragString, stringFragment)
                    .commit();

            stringFragment = (StringFragment) getSupportFragmentManager().findFragmentById(R.id.fragString);

            stringFragment.setText(string);

            break;
    }
}

The fragments have the same layout and class except for the name of textViews and layout.

ErrorFragment.java:

import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;

public class ErrorFragment extends Fragment {

    public View onCreateView(LayoutInflater inflater,ViewGroup container,Bundle savedInstanceState) {
        return inflater.inflate(R.layout.fragment_error,container,false);
    }

    public void setText(String text) {
        TextView textView = (TextView) getActivity().findViewById(R.id.errorOut);
        textView.setText(text);
    }
}

fragment_error.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">

    <TextView
        android:id="@+id/errorTitle"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="@string/error"
        android:textColor="#FF0000"
        android:textSize="25sp"
        android:gravity="center|top"/>

    <TextView
        android:id="@+id/errorOut"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginTop="10dp"
        android:textSize="20sp"
        android:text=""
        android:gravity="center|top"/>
</LinearLayout>

createFragment() is called by some buttons

After some tests I noticed that the fragment is created but when I call "errorFragment.setText;" the app crash. In the case 2 the app doesn't crash but the textview is not displayed (I noticed that if I click fast the button the textView appear for a few milliseconds)

EDIT: I tried to do that but the app still crash

Answer 1

Seem that the TextView you are trying to set text into is in the fragment layout. You should do it like this in both of your fragments.

The way you are trying to set text into the text view, android is trying to find it in the layout of activity not in the fragment's layout. That's why your app is crashing (probably NullPointerException )

private View view = null;
public View onCreateView(LayoutInflater inflater,ViewGroup container,Bundle savedInstanceState) {
    view = inflater.inflate(R.layout.fragment_error,container,false);
    return view;
}

public void setText(String text) {
    TextView textView = (TextView) view.findViewById(R.id.errorOut);
    textView.setText(text);
}

Answer 2

I think @Rohit5k2 is right in his explanation but instead of inflating the fragment layout in a View, you should use the same layout that you have in your XML file, which is a LinearLayout in your case.

So try this:

private LinearLayout layout = null;

public View onCreateView(LayoutInflater inflater,ViewGroup container,Bundle savedInstanceState) {
    layout = (LinearLayout) inflater.inflate(R.layout.fragment_error,container,false);
    return layout;
}

public void setText(String text) {
    TextView textView = (TextView) layout.findViewById(R.id.errorOut);
    textView.setText(text);
}