android 组件RecyclerView的使用指教？
想在首页使用RecyclerView来显示数据，因为使用了fragment所以我想在返回首页这一部分是填充数据，但是一直报错，这个控件不是太熟悉可以看看代码哪里有问题
MainActivaty
package com.example.fiz.myapplication;import android.graphics.Color;
import android.os.Bundle;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.Snackbar;
import android.support.v4.app.Fragment;
import android.support.v4.view.ViewPager;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.support.v7.widget.RecyclerView.ViewHolder;
import android.support.v7.widget.Toolbar;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.widget.LinearLayout;
import android.graphics.Color;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import java.util.ArrayList;
import android.support.v7.app.ActionBarActivity;
import android.support.v7.app.ActionBar;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentPagerAdapter;
import android.support.v4.view.ViewPager;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.LinearLayout;
import android.support.v7.widget.Toolbar;
import android.widget.TextView;
import java.util.ArrayList;
import java.util.List;
public class MainActivity extends AppCompatActivity {
private ViewPager mPager;
private ArrayList<Fragment> fragmentsList;
private LinearLayout ll_top;
//首页组件定义
private RecyclerView mRecyclerView;
private List<String> mDatas;
private HomeAdapter mAdapter;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
toolbar.setTitle("demo");
toolbar.setSubtitle("1234");
toolbar.setLogo(R.drawable.ic_launcher);
setSupportActionBar(toolbar);
initView();
}
private void initView() {
ll_top = (LinearLayout) findViewById(R.id.ll_top);
mPager = (ViewPager) findViewById(R.id.vPager);
fragmentsList = new ArrayList<Fragment>();
//首页个recelerView添加数据
// initData();
// mRecyclerView = (RecyclerView) findViewById(R.id.my_recycler_view);
// mRecyclerView.setLayoutManager(new LinearLayoutManager(this));
// mRecyclerView.setAdapter(mAdapter = new HomeAdapter());
//
Fragment activityfragment = TestFragment.newInstance("界面一");
Fragment groupFragment = TestFragment.newInstance("界面2");
Fragment friendsFragment = TestFragment.newInstance("界面3");
Fragment chatFragment = TestFragment.newInstance("界面4");
Fragment about = About.about("1234");
Fragment homepage = HomePage.homePage("首页");
fragmentsList.add(homepage);/**首页**/
fragmentsList.add(groupFragment);
fragmentsList.add(friendsFragment);
fragmentsList.add(chatFragment);
mPager.setAdapter(new MyFragmentPagerAdapter(
getSupportFragmentManager(), fragmentsList));
mPager.setCurrentItem(0);
BottomTabBar navigationBar = new BottomTabBar(this);
ll_top.setBackgroundColor(Color.parseColor("#F8F8FF"));
navigationBar.attachToParent(ll_top, new String[]{"首页", "消息", "发现",
"我"}, mPager);
}
protected void initData() {
mDatas = new ArrayList<String>();
for (int i = 'A'; i < 'z'; i++) {
mDatas.add("this is a demo---" + (char) i);
}
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_main, 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.
int id = item.getItemId();
//noinspection SimplifiableIfStatement
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
public class MyFragmentPagerAdapter extends FragmentPagerAdapter {
private ArrayList<Fragment> fragmentsList;
public MyFragmentPagerAdapter(FragmentManager fm) {
super(fm);
}
public MyFragmentPagerAdapter(FragmentManager fm,
ArrayList<Fragment> fragments) {
super(fm);
this.fragmentsList = fragments;
}
@Override
public int getCount() {
return fragmentsList.size();
}
@Override
public Fragment getItem(int arg0) {
return fragmentsList.get(arg0);
}
@Override
public int getItemPosition(Object object) {
return super.getItemPosition(object);
}
}
class HomeAdapter extends RecyclerView.Adapter<HomeAdapter.MyViewHolder>
{
@Override
public MyViewHolder onCreateViewHolder(ViewGroup parent, int viewType)
{
MyViewHolder holder = new MyViewHolder(LayoutInflater.from(
MainActivity.this).inflate(R.layout.item_home, parent,
false));
return holder;
}
@Override
public void onBindViewHolder(MyViewHolder holder, int position)
{
holder.tv.setText(mDatas.get(position));
}
@Override
public int getItemCount()
{
return mDatas.size();
}
class MyViewHolder extends ViewHolder
{
TextView tv;
public MyViewHolder(View view)
{
super(view);
tv = (TextView) view.findViewById(R.id.id_num);
}
}
}
}
布局文件
home_page
<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"
tools:context=".MainActivity">
<android.support.v7.widget.RecyclerView
android:id="@+id/my_recycler_view"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:scrollbars="vertical"/>
</RelativeLayout>
item_home
<?xml version="1.0" encoding="utf-8"?><FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:background="#44ff0000"
android:layout_height="wrap_content" >
<TextView
android:id="@+id/id_num"
android:layout_width="match_parent"
android:layout_height="50dp"
android:gravity="center"
android:text="1" />
</FrameLayout>
HomePage
@SuppressLint("ValidFragment")public class HomePage extends Fragment {
private String textString;
//首页组件
public HomePage(String textString) {
this.textString = textString;
}
public static HomePage homePage(String textString) {
HomePage myabout = new HomePage(textString);
return myabout;
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.home_page, container, false);
return view;
}
}
异常报错信息
03-19 23:41:20.809 3818-3818/? E/AndroidRuntime: FATAL EXCEPTION: main Process: com.example.fiz.myapplication, PID: 3818
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.fiz.myapplication/com.example.fiz.myapplication.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v7.widget.RecyclerView.setLayoutManager(android.support.v7.widget.RecyclerView$LayoutManager)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2416)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)
at android.app.ActivityThread.-wrap11(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v7.widget.RecyclerView.setLayoutManager(android.support.v7.widget.RecyclerView$LayoutManager)' on a null object reference
at com.example.fiz.myapplication.MainActivity.initView(MainActivity.java:77)
at com.example.fiz.myapplication.MainActivity.onCreate(MainActivity.java:64)
at android.app.Activity.performCreate(Activity.java:6237)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1107)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2369)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)
at android.app.ActivityThread.-wrap11(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
回答：
这句不能注释啊
// mRecyclerView.setLayoutManager(new LinearLayoutManager(this));我有个RecyclerView使用的Demo，可以看看
回答：
ava.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v7.widget.RecyclerView.setLayoutManager(android.support.v7.widget.RecyclerView$LayoutManager)' on a null object reference at com.example.fiz.myapplication.MainActivity.initView(MainActivity.java:77)
我觉得你需要看懂是哪里错误分析log。这里的错误信息写的很清楚MainActivity.java的77行有一个空指针错误
以上是 android 组件RecyclerView的使用指教？ 的全部内容， 来源链接： utcz.com/p/175870.html
