中調用的片段上加載列表視圖時我剛剛進入android編程。我無法在ListFragment上顯示Listview。我已經在一個活動上嘗試過它,但它工作得很完美,但是,我試圖在導航抽屜中調用的Listfragment上顯示相同的ListView,但是我的應用程序在單擊時崩潰。我已經這麼久了,試圖從不同的網站獲得答案,但都無濟於事。無法在導航菜單項
PLS:有點幫助將是好的,非常感謝
在logcat的顯示的錯誤是:
09-18 14:35:53.285
3602-3602/com.example.ceede.classwork E/AndroidRuntime: FATAL
EXCEPTION: main Process: com.example.ceede.classwork, PID: 3602
java.lang.NullPointerException at
com.example.ceede.classwork.MainActivity.onNavigationItemSelected(MainActivity.java:92)
at
android.support.design.widget.NavigationView$1.onMenuItemSelected(NavigationView.java:152)
content_main.xml
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
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"
app:layout_behavior="@string/appbar_scrolling_view_behavior"
tools:context="com.example.ceede.classwork.MainActivity"
tools:showIn="@layout/app_bar_main">
<fragment
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:name="android.support.v4.app.ListFragment"
android:id="@+id/fragment"
android:layout_alignParentTop="true"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true" />
</RelativeLayout>
CustomAdapter.java
package com.example.ceede.classwork;
import android.content.Context;
import android.content.res.Resources;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.ImageView;
import android.widget.TextView;
import java.util.ArrayList;
public class CustomAdapter extends BaseAdapter {
ArrayList<SingleRow> list;
Context context;
CustomAdapter(Context context) {
list = new ArrayList<>();
this.context = context;
Resources res = context.getResources();
String[] titles = res.getStringArray(R.array.Titles);
int[] images = {R.drawable.admisntrationicon, R.drawable.articon, R.drawable.businesseducationicon,
R.drawable.homeicon, R.drawable.drivericon, R.drawable.stafficon,
R.drawable.counciloricon, R.drawable.physicalcon, R.drawable.englishicon,
R.drawable.mathsicon, R.drawable.scienceicon, R.drawable.historyicon,
R.drawable.suporticon};
for (int i = 0; i < titles.length; i++) {
list.add(new SingleRow(titles[i], images[i]));
}
}
@Override
public int getCount() {
return list.size();
}
@Override
public Object getItem(int i) {
return list.get(i);
}
@Override
public long getItemId(int i) {
return i;
}
@Override
public View getView(int i, View view, ViewGroup viewGroup) {
SingleRow temp = list.get(i);
View row = null;
if(view==null)
{
LayoutInflater inflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
row=inflater.inflate(R.layout.single_row,viewGroup,false);
}
TextView titles= (TextView) row.findViewById(R.id.textAdmin);
ImageView image= (ImageView)row.findViewById(R.id.adminImage);
return row;
}
}
SingleRow.java
class SingleRow {
public String titles;
public int images;
SingleRow(String titles, int images) {
this.titles = titles;
this.images = images;
}
}
MyFragmentClass.java
package com.example.ceede.classwork;
import android.os.Bundle;
import android.support.annotation.Nullable;
import android.support.v4.app.Fragment;
import android.support.v4.app.ListFragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ListView;
public class MyFirstFragment extends ListFragment {
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
return inflater.inflate(R.layout.my_list_fragment,container,false);
}
@Override
public void onActivityCreated(@Nullable Bundle savedInstanceState) {
super.onActivityCreated(savedInstanceState);
ListView listView= (ListView) getActivity().findViewById(R.id.listView);
listView.setAdapter(new CustomAdapter(getActivity()));
}
public static Fragment newInstance() {
MyFirstFragment frag=new MyFirstFragment();
return frag;
}
}
MainActivity
package com.example.ceede.classwork;
import android.os.Bundle;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.Snackbar;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentTransaction;
import android.view.View;
import android.support.design.widget.NavigationView;
import android.support.v4.view.GravityCompat;
import android.support.v4.widget.DrawerLayout;
import android.support.v7.app.ActionBarDrawerToggle;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.Menu;
import android.view.MenuItem;
public class MainActivity extends AppCompatActivity
implements NavigationView.OnNavigationItemSelectedListener {
FragmentManager manager;
FragmentTransaction transaction;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
fab.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
.setAction("Action", null).show();
}
});
DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(
this, drawer, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close);
drawer.setDrawerListener(toggle);
toggle.syncState();
NavigationView navigationView = (NavigationView) findViewById(R.id.nav_view);
navigationView.setNavigationItemSelectedListener(this);
}
@Override
public void onBackPressed() {
DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
if (drawer.isDrawerOpen(GravityCompat.START)) {
drawer.closeDrawer(GravityCompat.START);
} else {
super.onBackPressed();
}
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.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);
}
@SuppressWarnings("StatementWithEmptyBody")
@Override
public boolean onNavigationItemSelected(MenuItem item) {
// Handle navigation view item clicks here.
int id = item.getItemId();
if (id == R.id.contact) {
// Handle the camera action
//Line 92. This is the Line of code causing the error
FragmentManager manager=getSupportFragmentManager();
FragmentTransaction transaction=manager.beginTransaction();
transaction.replace(R.id.fragment, MyFirstFragment.newInstance());
transaction.commit();
}
DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
drawer.closeDrawer(GravityCompat.START);
return true;
}
}
您的logcat顯示NPE出現在MainActivity.java行92.您爲** MainActivity.java **提供的代碼僅包含83行...請更正此錯誤並向我們顯示錯誤發生的位置(例如在MainActivity代碼中插入註釋)。 – gus27
@ gus42我編輯了代碼,並對標記錯誤的代碼行進行了評論。 (92行),但是,我仍然得到同樣的錯誤。謝謝 –