碎片中的Android致命异常

Question

package com.example.yatisawhney.fragmentdemo;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;

public class MainActivity extends AppCompatActivity implements TopFragment.ActivityCommunicator {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
    }

    @Override
    public void changeText(String a, String b) {
        BottomFragment bf = (BottomFragment)getSupportFragmentManager().findFragmentById(R.id.fragment2);
        bf.setMeme(a,b);
    }
}

package com.example.yatisawhney.fragmentdemo;

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

/**
 * Created by yatisawhney on 28/05/16.
 */
public class BottomFragment extends Fragment {
    private static TextView top ;
    private static TextView bottom;

    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        View bottom = inflater.inflate(R.layout.bottom_section ,container, false);

        top = (TextView)bottom.findViewById(R.id.textView);
        bottom=(TextView)bottom.findViewById(R.id.textView2);

        return bottom;
    }

    public void setMeme(String a , String b){
        top.setText(a);
        bottom.setText(b);
    }
}

顶部碎片

package com.example.yatisawhney.fragmentdemo;

import android.app.Activity;
import android.os.Bundle;
import android.support.annotation.Nullable;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.EditText;

/**
 * Created by yatisawhney on 28/05/16.
 */
public class TopFragment extends Fragment{

    private static  EditText top;
    private static EditText bottom;

    ActivityCommunicator communicator;


    public interface ActivityCommunicator{
        public void changeText(String a , String b);
    }

    private void changeText(){
        communicator.changeText(top.getText().toString() , bottom.getText().toString());
    }

    @Override
    public void onAttach(Activity activity) {
        super.onAttach(activity);
        try {
            communicator = (ActivityCommunicator) activity;
        }catch(Exception e){
            e.printStackTrace();
        }
    }

    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        View top_view = inflater.inflate(R.layout.top_section , container , false);

        top=(EditText)top_view.findViewById(R.id.yates_text);
        bottom=(EditText)top_view.findViewById(R.id.yates_another_text);
        Button button = (Button)top_view.findViewById(R.id.yates_button);
        button.setOnClickListener(
                new View.OnClickListener() {
                    @Override
                    public void onClick(View v) {
                        changeText();
                    }
                }
        );

        return top_view;
    }
}

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="com.example.yatisawhney.fragmentdemo.MainActivity">

    <fragment
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:name="com.example.yatisawhney.fragmentdemo.TopFragment"
        android:id="@+id/fragment"
        android:layout_alignParentTop="true"
        android:layout_centerHorizontal="true"
        tools:layout="@layout/top_section" />

    <fragment
        android:layout_width="300dp"
        android:layout_height="300dp"
        android:name="com.example.yatisawhney.fragmentdemo.BottomFragment"
        android:id="@+id/fragment2"
        tools:layout="@layout/bottom_section"
        android:layout_alignParentBottom="true"
        android:layout_centerHorizontal="true" />

</RelativeLayout>

Answer 1

我终于得到了我的问题的答案。

片段生命周期的onCreate可能在活动生命周期的onCreate期间调用。但并不是所有时候都是这样

因此，为了安全起见，如果您希望以片段形式访问视图，请在onActivityCreated（）方法中访问。这将确认活动已经创建并且视图层次结构已经加载到内存中。：）