问题描述

从activity调用ViewPager里Fragment的方法传参出现空指针异常？

报错信息如下：
FATAL EXCEPTION: main
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.thefat.lingjunqi.enricher/com.thefat.lingjunqi.enricher.ActivityReading}: java.lang.NullPointerException
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2308)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
at android.app.ActivityThread.access$600(ActivityThread.java:156)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1342)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:153)
at android.app.ActivityThread.main(ActivityThread.java:5338)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:511)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:833)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:600)
at dalvik.system.NativeStart.main(Native Method)

Caused by: java.lang.NullPointerException

at com.thefat.lingjunqi.enricher.FragmentArticleEN.refresh(FragmentArticleEN.java:32)
at com.thefat.lingjunqi.enricher.ActivityReading.onCreate(ActivityReading.java:103)
at android.app.Activity.performCreate(Activity.java:5232)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1081)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2272)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)?
at android.app.ActivityThread.access$600(ActivityThread.java:156)?
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1342)?
at android.os.Handler.dispatchMessage(Handler.java:99)?
at android.os.Looper.loop(Looper.java:153)?
at android.app.ActivityThread.main(ActivityThread.java:5338)?
at java.lang.reflect.Method.invokeNative(Native Method)?
at java.lang.reflect.Method.invoke(Method.java:511)?
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:833)?
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:600)?
at dalvik.system.NativeStart.main(Native Method)

ActivityReading.class

 package com.thefat.lingjunqi.enricher;

import android.content.Context;
import android.content.Intent;
import android.graphics.BitmapFactory;
import android.graphics.Matrix;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentActivity;
import android.support.v4.view.ViewPager;
import android.util.DisplayMetrics;
import android.view.MenuItem;
import android.view.View;
import android.view.animation.Animation;
import android.view.animation.TranslateAnimation;
import android.widget.ImageView;
import android.widget.TextView;

import java.util.ArrayList;

public class ActivityReading extends FragmentActivity {

    private ViewPager mPager;
    private ArrayList<Fragment> fragmentsList;
    private ImageView bottomLine;
    private TextView textView1, textView2, textView3;

    private int currIndex = 0;
    private int bottomLineWidth;
    private int offset = 0;

    /*String [] articleTitle;
    String [] articleContent;
    String [] transTitle;
    String [] transContent;
    String wordsTitle;
    String [] wordsContent;*/

    public static final String ITEM_ID = "item_id";

    int color_current;
    int color_notCurrent;

    public static void actionStart(Context context, int id){
        Intent intent=new Intent(context,ActivityReading.class);
        intent.putExtra(ActivityReading.ITEM_ID,id);
        context.startActivity(intent);
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_reading);

        mPager = (ViewPager) findViewById(R.id.viewpager);

        getActionBar().setDisplayHomeAsUpEnabled(true);

        color_current=getResources().getColor(R.color.color_current);
        color_notCurrent =getResources().getColor(R.color.color_notcurrent);
        String [] articleTitle=getResources().getStringArray(R.array.lesson_name_list_en);
        String []articleContent=getResources().getStringArray(R.array.array_article);
        String []transTitle=getResources().getStringArray(R.array.lesson_name_list_cn);
        String []transContent=getResources().getStringArray(R.array.array_trans);
        String wordsTitle=getResources().getString(R.string.words_title);
        String []wordsContent=getResources().getStringArray(R.array.array_words);

        initImageView();

        int index=getIntent().getIntExtra(ActivityReading.ITEM_ID,0);

        textView1 = (TextView) findViewById(R.id.text1);
        textView2 = (TextView) findViewById(R.id.text2);
        textView3 = (TextView) findViewById(R.id.text3);

        textView1.setOnClickListener(new MyOnClickListener(0));
        textView2.setOnClickListener(new MyOnClickListener(1));
        textView3.setOnClickListener(new MyOnClickListener(2));

        final TextView[] titles = {textView1, textView2, textView3};

        fragmentsList = new ArrayList<>();

        FragmentArticleEN fragmentArticleEN = new FragmentArticleEN();
        FragmentArticleCN fragmentArticleCN = new FragmentArticleCN();
        FragmentWords fragmentWords = new FragmentWords();

        fragmentsList.add(fragmentArticleEN);
        fragmentsList.add(fragmentArticleCN);
        fragmentsList.add(fragmentWords);

        MyFragmentPagerAdapter Pageradapter=new MyFragmentPagerAdapter(getSupportFragmentManager(), fragmentsList);
        mPager.setAdapter(Pageradapter);
        mPager.setCurrentItem(0);

        FragmentArticleEN fragmentArticleEN_ = (FragmentArticleEN) Pageradapter.instantiateItem(mPager,0);
        FragmentArticleCN fragmentArticleCN_ = (FragmentArticleCN) Pageradapter.instantiateItem(mPager,1);
        FragmentWords fragmentWords_= (FragmentWords) Pageradapter.instantiateItem(mPager,2);

        fragmentArticleEN_.refresh(articleTitle[index],articleContent[index]);
        fragmentArticleCN_.refresh(transTitle[index],transContent[index]);
        fragmentWords_.refresh(wordsTitle,wordsContent[index]);

        mPager.setOnPageChangeListener(new ViewPager.OnPageChangeListener() {
            int one=offset*2+bottomLineWidth;//页卡1->页卡2偏移量

            @Override
            public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {

            }

            @Override
            public void onPageSelected(int position) {
                Animation animation=new TranslateAnimation(one*currIndex,one*position,0,0);
                animation.setFillAfter(true);
                animation.setDuration(250);
                bottomLine.startAnimation(animation);
                titles[currIndex].setTextColor(color_notCurrent);
                titles[position].setTextColor(color_current);
                currIndex=position;
            }

            @Override
            public void onPageScrollStateChanged(int state) {

            }
        });

    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        if (item.getItemId() == android.R.id.home) {
            //创建启动ActivityTitle的Intent
            Intent intent = new Intent(this, ActivityTitle.class);

            //添加额外的Flag，将Activity栈中处于FirstActivity之上的Activity弹出
            intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);

            //启动intent对应的Activity
            startActivity(intent);
            return true;
        }
        return super.onOptionsItemSelected(item);
    }

    private void initImageView() {
        bottomLine = (ImageView)findViewById(R.id.cursor);
        bottomLineWidth = BitmapFactory.decodeResource(getResources(), R.drawable.cursor).getWidth();
        DisplayMetrics dm = new DisplayMetrics();
        getWindowManager().getDefaultDisplay().getMetrics(dm);
        int screenW_Phone = dm.widthPixels;
        offset = (screenW_Phone/3 - bottomLineWidth)/2;

        //imgageview设置平移，使下划线平移到初始位置（平移一个offset）
        Matrix matrix = new Matrix();
        matrix.postTranslate(offset, 0);
        bottomLine.setImageMatrix(matrix);

    }

    public class MyOnClickListener implements View.OnClickListener {
        private int index = 0;

        public MyOnClickListener(int i) {
            index = i;
        }

        @Override
        public void onClick(View v) {
            mPager.setCurrentItem(index);
        }
    }
}

FragmentArticleEN.class

 package com.thefat.lingjunqi.enricher;

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 lingjunqi on 2015/12/2.
 */

public class FragmentArticleEN extends Fragment {
    private View view;

    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        view=inflater.inflate(R.layout.fragment_fragment_article_en,container,false);
        return view;
    }

    public void refresh(String title, String content){
        View visibilityLayout=view.findViewById(R.id.visibility_layout);
       visibilityLayout.setVisibility(View.VISIBLE);

        TextView articleTitleText=(TextView)view.findViewById(R.id.article_titile);
        TextView articleContentText=(TextView)view.findViewById(R.id.article_content);

        articleTitleText.setText(title);
        articleContentText.setText(content);
    }

}

如果我采用的方法错误，谁能告诉一下正确的从一个activity向另一个activity内的ViewPager里的fragment传参或者调用它的方法。

解决方案

自己调试，看看谁是空就行了，传参数，可以通过广播

解决方案二：

或者注册回调函数（监听）

解决方案三：

Activity 中
fragment.setArguments(bundle)

Fragment 中 fragment.getArguments();