Question

我的导航抽屉里有一个RecyclerView。我一直得到一个空指针异常。我看过类似的问题，但似乎没有一个解决方案。请帮忙。我不知道问题是什么。 Gradle具有所有必需的依赖项。

activity_expert.xml

 <android.support.v4.widget.DrawerLayout     xmlns:android="http://schemas.android.com/apk/res/android"
  android:layout_width="match_parent"
  android:layout_height="match_parent"
  android:id="@+id/drawerlayout">

<!--Content Section-->
<FrameLayout
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:id="@+id/mainContent">

    <include layout="@layout/toolbar"></include>

    <!--Main Content-->
    <android.support.v7.widget.RecyclerView
        android:layout_height="wrap_content"
        android:layout_width="match_parent"
        android:id="@+id/mainContentView">
    </android.support.v7.widget.RecyclerView>

    </FrameLayout>

<!--Drawer section-->

    <android.support.v7.widget.RecyclerView
        android:layout_width="240dp"
        android:layout_height="wrap_content"
        android:id="@+id/drawer_recycler_view"
        android:layout_gravity="start"
        android:background="@color/white"
        android:scrollbars="vertical">
    </android.support.v7.widget.RecyclerView>

drawer_header.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
     android:layout_width="match_parent"
     android:layout_height="200dp"
     android:background="@drawable/slider_3_small">

</RelativeLayout>

drawer_row.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="wrap_content"
    android:paddingTop="8dp"
    android:paddingBottom="8dp"
    android:layout_height="wrap_content"
    android:background="#ffffff"
    android:orientation="horizontal">


<ImageView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:id="@+id/rowIcon"
    android:paddingLeft="16dp"
    android:src="@drawable/cow_icon"/>

<TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:paddingLeft="12dp"
    android:paddingTop="4dp"
    android:textAppearance="?android:attr/textAppearanceMedium"
    android:text="Medium Text"
    android:id="@+id/rowText"
    />

 </LinearLayout>

ExpertActivity.java

 package com.lavineoluoch.myapplication.cowsoko;

 import android.app.ActionBar;
 import android.app.SearchManager;
 import android.app.SearchableInfo;
 import android.content.Context;
 import android.support.v4.widget.DrawerLayout;
 import android.support.v7.app.ActionBarActivity;
 import android.os.Bundle;
 import android.support.v7.app.ActionBarDrawerToggle;
 import android.support.v7.app.AppCompatActivity;
 import android.support.v7.widget.LinearLayoutManager;
 import android.support.v7.widget.RecyclerView;
 import android.support.v7.widget.SearchView;
 import android.support.v7.widget.Toolbar;
 import android.text.Layout;
 import android.view.Menu;
 import android.view.MenuItem;

 import com.lavineoluoch.myapplication.cowsoko.appUtils.DrawerAdapter;


 import java.util.ArrayList;
 import java.util.List;


 public class ExpertActivity extends AppCompatActivity {
//Data used to populate RecyclerView
String TITLES[] = {"Buy a Cow","Meet an Expert","Model Farms","Share","Rate","Settings"};
int ICONS[] = {R.drawable.cow_icon,R.drawable.expert_icon,R.drawable.farm_icon,R.drawable.share,R.drawable.rate,R.drawable.settings};


private Toolbar toolbar;
private DrawerLayout drawerLayout;
private RecyclerView recyclerView;




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

    drawerLayout = (DrawerLayout)findViewById(R.id.drawerlayout);
    recyclerView = (RecyclerView)findViewById(R.id.drawer_recycler_view);

    ActionBarDrawerToggle drawerToggle = new ActionBarDrawerToggle(this,drawerLayout,R.string.app_name,R.string.app_name);
    drawerLayout.setDrawerListener(drawerToggle);
    drawerToggle.syncState();


    DrawerAdapter drawerAdapter = new DrawerAdapter(TITLES,ICONS);
    recyclerView.setAdapter(drawerAdapter);
    recyclerView.setHasFixedSize(true);
    recyclerView.setLayoutManager(new LinearLayoutManager(this));

    toolbar = (Toolbar)findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);
    getSupportActionBar().setTitle("Meet an Expert");
    }


@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_expert, menu);

    //Insert Search View into toolbar
    MenuItem item = menu.findItem(R.id.action_search);
    SearchView searchView = (SearchView) menu.findItem(R.id.action_search).getActionView();
    SearchManager searchManager = (SearchManager) getSystemService(Context.SEARCH_SERVICE);
    SearchableInfo info = searchManager.getSearchableInfo(getComponentName());
    searchView.setSearchableInfo(info);
    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);
}

}

最后是DrawerAdapter.java

package com.lavineoluoch.myapplication.cowsoko.appUtils;

import android.provider.Telephony;
import android.support.v7.widget.RecyclerView;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageView;
import android.widget.TextView;

import com.lavineoluoch.myapplication.cowsoko.R;

import java.util.List;

import butterknife.ButterKnife;
import butterknife.InjectView;

/**
* Created by USER on 8/7/2015.
*
* This class is the RecyclerView Adapter
*/
public class DrawerAdapter extends     RecyclerView.Adapter<DrawerAdapter.ViewHolder> {

private static final int HEADER_TYPE = 0;
private static final int ITEM_TYPE = 1;
private String NavTitles[];
private int NavIcons[];


public DrawerAdapter(String NavTitles[],int NavIcons[]) {
    this.NavTitles = NavTitles;
    this.NavIcons = NavIcons;
}

//Called whenever a new instance of our ViewHolder class is created
@Override
public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
   if (viewType == ITEM_TYPE){
       View v = LayoutInflater.from(parent.getContext()).inflate(R.layout.drawer_row,parent,false);
       ViewHolder viewHolderItem = new ViewHolder(v,viewType);
       return viewHolderItem;
   }else if (viewType == HEADER_TYPE){
       View v = LayoutInflater.from(parent.getContext()).inflate(R.layout.drawer_header,parent,false);
       ViewHolder viewHolderHeader = new ViewHolder(v,viewType);
       return viewHolderHeader;
   }

    return null;
}

//Called when the SO binds the view with the data -- or, in other words, the data is shown in the UI
@Override
public void onBindViewHolder(ViewHolder holder, int position) {
    if (holder.holderId == 1){
       holder.textView.setText(NavTitles[position - 1]);
       holder.imageView.setImageResource(NavIcons[position - 1]);
    }

}

@Override
public int getItemCount() {

    return NavTitles.length + 1;    }

@Override
public int getItemViewType(int position) {
    if (position == 0)
        return HEADER_TYPE;

    return ITEM_TYPE;

}


/**
 * A ViewHolder describes an item view and metadata about its place within the RecyclerView.
 * RecyclerView.Adapter implementations should subclass ViewHolder and add fields for
 * caching potentially expensive findViewById(int) results.
 *
 */


public static class ViewHolder extends RecyclerView.ViewHolder{
    protected int holderId;
    @InjectView(R.id.rowIcon)ImageView imageView;
    @InjectView(R.id.rowText)TextView textView;

    /**
     *
     * @param itemView
     * @param viewType
     */
    public ViewHolder(View itemView,int viewType) {

        super(itemView);

        this.holderId = viewType;
        if (viewType == ITEM_TYPE){
            ButterKnife.inject(this,itemView);
            holderId = 1;
        }else {
            holderId = 0;
        }
    }
}

}

我的logcat看起来像这样

08-08 19：26：35.847 18694-18694 / com.lavineoluoch.myapplication.cowsoko E / AndroidRuntime：FATAL EXCEPTION：main 显示java.lang.NullPointerException 在android.support.v7.widget.RecyclerView.onMeasure（RecyclerView.java:1764）在android.view.View.measure（View.java:16030）在android.view.ViewGroup.measureChildWithMargins（ViewGroup.java:5012）在android.widget.FrameLayout.onMeasure（FrameLayout.java:310）在android.view.View.measure（View.java:16030）在android.support.v4.widget.DrawerLayout.onMeasure（DrawerLayout.java:868）在android.view.View.measure（View.java:16030）

Answer 1

我使用此代码来解决此问题：

LayoutInflater layoutInflater = (LayoutInflater)getSystemService(LAYOUT_INFLATER_SERVICE);
View view = layoutInflater.inflate(R.layout.nav_header, mNavigationView);

导航抽屉空指针异常

1 个答案: