想把GridView添加到ViewPager里面。加载无效
用TabLayout和ViewPager关联后，想把GridView添加到ViewPager里面。报空指针异常。
上面那个问题解决了，没有加载layout所以空对象。
View view = this.getLayoutInflater().inflate(R.layout.grid_view,null);
现在不报错，但是GridView没有加载进来，各位大神帮忙看一下是不是适配器写错了
04-12 08:39:37.363 25278-25278/? E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.chenshenglei.tablayouttest, PID: 25278
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.chenshenglei.tablayouttest/com.example.chenshenglei.tablayouttest.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.GridView.setAdapter(android.widget.ListAdapter)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2646)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2707)
at android.app.ActivityThread.-wrap12(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1460)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6077)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:866)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:756)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.GridView.setAdapter(android.widget.ListAdapter)' on a null object reference
at com.example.chenshenglei.tablayouttest.MainActivity.onCreate(MainActivity.java:46)
at android.app.Activity.performCreate(Activity.java:6662)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1118)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2599)
下面贴代码MyGridViewAdapter.java
import android.content.Context;
import android.view.View;
import android.view.ViewGroup;
import android.widget.SimpleAdapter;
import java.util.List;
import java.util.Map;
/**
* Created by chenshenglei on 18-4-12.
*/
public class MyGridViewAdapter extends SimpleAdapter {
private Context mContext;
public MyGridViewAdapter(Context context, List<Map<String, Object>> dataLists, int layout, String[] key, int[] item){
super(context, dataLists,layout, key, item);
this.mContext = context;
}
@Override
public int getCount() {
return 0;
}
@Override
public Object getItem(int position) {
return null;
}
@Override
public long getItemId(int position) {
return 0;
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
convertView = super.getView(position, convertView, parent);
return convertView;
}
}
代码TabPagerAdapter.java
package com.example.chenshenglei.tablayouttest;
import android.content.Context;
import android.support.v4.view.PagerAdapter;
import android.support.v4.view.ViewPager;
import android.view.Gravity;
import android.view.View;
import android.view.ViewGroup;
import android.widget.GridView;
import android.widget.TextView;
import java.security.PublicKey;
import java.util.List;
/**
* Created by chenshenglei on 18-4-12.
*/
//自定义ViewPager页面适配器
public class TabPagerAdapter extends PagerAdapter {
private Context mContext;
private String[] mTitleArray;
private List<GridView> mList;
public TabPagerAdapter (Context context, String[] title) {
super();
this.mContext = context;
this.mTitleArray = title;
}
public TabPagerAdapter (Context context, String[] title, List<GridView> array) {
super();
this.mContext = context;
this.mTitleArray = title;
this.mList = array;
}
@Override
public int getCount() {
return mTitleArray.length;
}
@Override
public boolean isViewFromObject(View view, Object object) {
return view == object;
}
@Override
public Object instantiateItem(ViewGroup container, int position) {
View view = mList.get(position);
container.addView(view);
return view;
}
@Override
public void destroyItem(ViewGroup container, int position, Object object) {
container.removeView((View) object);
}
@Override
public CharSequence getPageTitle(int position) {
return mTitleArray[position];
}
}
代码 MainActivity.java
import android.support.design.widget.TabLayout;
import android.support.v4.view.ViewPager;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.GridView;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
public class MainActivity extends AppCompatActivity {
private TabLayout mTabLayout;
private ViewPager mViewPager;
private String[] mTitleArray = {"酒标","葡萄品种"};
private GridView gridView1;
private GridView gridView2;
private MyGridViewAdapter myGridViewAdapter;
private List<GridView> mList;
private List<Map<String, Object>> dataList;
private List<Map<String, Object>> dataList2;
private int[] img = {R.mipmap.ic_launcher_round,R.mipmap.ic_launcher};
private int[] img2 = {R.mipmap.ic_launcher_round,R.mipmap.ic_launcher};
private String[] imgName = {"1","2"};
private String[] imgName2 = {"3","4"};
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_weibo_timeline);
gridView1 = (GridView)findViewById(R.id.grid_test);
dataList = new ArrayList<Map<String, Object>>();
myGridViewAdapter = new MyGridViewAdapter(this,
getData(), R.layout.grid_item,
new String[] {"img", "txt"},
new int[] {R.id.img_item,R.id.txt_item});
gridView1.setAdapter(myGridViewAdapter);
gridView2 = (GridView)findViewById(R.id.grid_test);
dataList2 = new ArrayList<Map<String, Object>>();
myGridViewAdapter = new MyGridViewAdapter(this,
getData2(), R.layout.grid_item,
new String[] {"img", "txt"},
new int[] {R.id.img_item,R.id.txt_item});
gridView2.setAdapter(myGridViewAdapter);
mList = new ArrayList<GridView>();
mList.add(gridView1);
mList.add(gridView2);
mViewPager = (ViewPager) findViewById(R.id.view);
TabPagerAdapter adapter = new TabPagerAdapter(getApplicationContext(),mTitleArray,mList);
mViewPager.setAdapter(adapter);
mTabLayout = (TabLayout) findViewById(R.id.tab);
mTabLayout.setupWithViewPager(mViewPager);
}
private List<Map<String,Object>> getData() {
for (int i=0; i<img.length; i++) {
Map<String,Object> map = new HashMap<String, Object>();
map.put("img", img[i]);
map.put("txt", imgName[i]);
dataList.add(map);
}
return dataList;
}
private List<Map<String,Object>> getData2() {
for (int i=0; i<img.length; i++) {
Map<String,Object> map = new HashMap<String, Object>();
map.put("img", img2[i]);
map.put("txt", imgName2[i]);
dataList2.add(map);
}
return dataList2;
}
}
grid_view.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">
<GridView
android:id="@+id/grid_test"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:numColumns="4"
android:verticalSpacing="5dp"
android:horizontalSpacing="5dp"
android:layout_marginTop="40dp"/>
</LinearLayout>
grid_item.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"
android:gravity="center"
android:background="#ffffff">
<ImageView
android:id="@+id/img_item"
android:src="@mipmap/ic_launcher"
android:layout_width="wrap_content"
android:layout_height="wrap_content" />
<TextView
android:id="@+id/txt_item"
android:textColor="#000000"
android:text="文字区域"
android:layout_width="wrap_content"
android:layout_height="wrap_content" />
</LinearLayout>```
activity_weibo_timeline.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">
<android.support.v4.view.ViewPager
android:id="@+id/view"
android:layout_width="match_parent"
android:layout_height="0dp"
android:layout_weight="1"/>
<LinearLayout
android:layout_width="200dp"
android:layout_height="wrap_content"
android:layout_gravity="center_horizontal">
<android.support.design.widget.TabLayout
android:id="@+id/tab"
android:layout_width="match_parent"
android:layout_height="wrap_content"
app:tabMode="scrollable"/>
</LinearLayout>
</LinearLayout>
建议将 grid_view.xml 替换成下面的
android:id="@+id/grid_test"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:numColumns="4"
android:verticalSpacing="5dp"
android:horizontalSpacing="5dp"
>
代码里：
gridView1 = (GridView) this.getLayoutInflater().inflate(R.layout.grid_view,null);
gridView2 = (GridView) this.getLayoutInflater().inflate(R.layout.grid_view,null);
方法一：
public class MyGridViewAdapter extends SimpleAdapter {
private Context mContext;
private List<Map<String, Object>> mMataLists;
public MyGridViewAdapter(Context context, List<Map<String, Object>> dataLists, int layout, String[] key, int[] item){
super(context, dataLists,layout, key, item);
this.mContext = context;
this.mMataLists = dataLists == null ? new ArrayList<Map<String, Object>>() : dataLists;
}
@Override
public int getCount() {
return mMataLists.size();
}
// 下面方法代码不变，不粘贴了
}
方法二：
直接使用 SimpleAdapter；
private SimpleAdapter myGridViewAdapter;
myGridViewAdapter = new SimpleAdapter(MainActivity.this,
getData(), R.layout.grid_item,
new String[] {"img", "txt"},
new int[] {R.id.img_item,R.id.txt_item});
gridView1.setAdapter(myGridViewAdapter);
这样可以正常显示了
看就是 MainActivity的 调用 XXX.setAdapter 这里的XXX控件是null呀 检查一下 控件id是不是正确
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.GridView.setAdapter(android.widget.ListAdapter)' on a null object reference
gridView1.setAdapter(myGridViewAdapter);
这个GridView为空
试试下面的代码
@Override
public Object instantiateItem(ViewGroup container, int position) {
GridView gridview = mList.get(position % mList.size());
container.addView(gridview);
return gridview;
}
适配器重写的方法错了吧
gridView1 = (GridView)findViewById(R.id.grid_test);
gridView2 = (GridView)findViewById(R.id.grid_test);
同一个控件，在同一个界面怎么能赋值两次？第二次肯定会找不到啊，gridView2报空
你的GridView的adapter的
@Override
public int getCount() {
return 0;
}
这里返回0在gridView是不会添加控件的，simpleAdapter已经写好了，不需要重写这么多方法。
上面的布局代码没有粘贴完，下面重新发表一下，解决GridView内容不显示的方法还是上面的两个方法
建议将 grid_view.xml 替换成下面的
<?xml version="1.0" encoding="utf-8"?>
android:id="@+id/grid_test"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:numColumns="4"
android:verticalSpacing="5dp"
android:horizontalSpacing="5dp"
>
代码里：
gridView1 = (GridView) this.getLayoutInflater().inflate(R.layout.grid_view,null);
gridView2 = (GridView) this.getLayoutInflater().inflate(R.layout.grid_view,null);
