ListView.setAdapter - java.lang.NullPointerException
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ListView.setAdapter - java.lang.NullPointerException
提问by kbu
Could anybody explain me, why i have java.lang.NullPointerException when i am trying setAdapter?
谁能解释一下，为什么我在尝试 setAdapter 时会出现 java.lang.NullPointerException？
When i trying set Adapter, my arraylist already filled. What i making wrong?
当我尝试设置适配器时，我的数组列表已经填满了。我做错了什么？
Thx!
谢谢！
activity_view_list.xml
活动视图列表.xml
<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical">
<ListView
android:id="@+id/lvView"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:layout_weight="1">
</ListView>
</LinearLayout>
item.xml
项目.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:orientation="horizontal">
<ImageView
android:id="@+id/ivImage"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:src="@drawable/ic_launcher">
</ImageView>
<LinearLayout
android:id="@+id/linearLayout1"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:layout_marginLeft="5dp"
android:layout_weight="1"
android:orientation="vertical">
<TextView
android:id="@+id/tvDescr"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginTop="5dp"
android:text=""
android:textSize="20sp">
</TextView>
</LinearLayout>
</LinearLayout>
My class for products
我的产品类
package com.shvedchenko.skleroshop;
/**
* Created by dima on 14.08.13.
*/
public class Product {
String name;
int image;
Product(String _describe, int _image) {
name = _describe;
image = _image;
}
}
And my BoxAdapter
还有我的 BoxAdapter
package com.shvedchenko.skleroshop;
import android.content.Context;
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;
/**
* Created by dima on 14.08.13.
*/
public class BoxAdapter extends BaseAdapter {
Context ctx;
LayoutInflater lInflater;
ArrayList<Product> objects;
BoxAdapter(Context context, ArrayList<Product> products) {
ctx = context;
objects = products;
lInflater = (LayoutInflater) ctx
.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
}
// кол-во элементов
@Override
public int getCount() {
return objects.size();
}
// элемент по позиции
@Override
public Object getItem(int position) {
return objects.get(position);
}
// id по позиции
@Override
public long getItemId(int position) {
return position;
}
// пункт списка
@Override
public View getView(int position, View convertView, ViewGroup parent) {
// используем созданные, но не используемые view
View view = convertView;
if (view == null) {
view = lInflater.inflate(R.layout.item, parent, false);
}
Product p = getProduct(position);
// заполняем View в пункте списка данными из товаров: наименование, цена
// и картинка
((TextView) view.findViewById(R.id.tvDescr)).setText(p.name);
((ImageView) view.findViewById(R.id.ivImage)).setImageResource(p.image);
return view;
}
// товар по позиции
Product getProduct(int position) {
return ((Product) getItem(position));
}
}
ERRORS
错误
08-14 08:38:29.684 511-511/com.shvedchenko.skleroshop W/dalvikvm: threadid=3: thread exiting with uncaught exception (group=0x4001b188)
08-14 08:38:29.684 511-511/com.shvedchenko.skleroshop E/AndroidRuntime: Uncaught handler: thread main exiting due to uncaught exception
08-14 08:38:29.694 511-511/com.shvedchenko.skleroshop E/AndroidRuntime: java.lang.RuntimeException: Unable to start activity ComponentInfo{com.shvedchenko.skleroshop/com.shvedchenko.skleroshop.ViewList}: java.lang.NullPointerException
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2496)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2512)
at android.app.ActivityThread.access00(ActivityThread.java:119)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1863)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:123)
at android.app.ActivityThread.main(ActivityThread.java:4363)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:521)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:860)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:618)
at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.NullPointerException
at com.shvedchenko.skleroshop.ViewList.onCreate(ViewList.java:37)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2459)
ViewList.java
视图列表.java
package com.shvedchenko.skleroshop;
import android.app.ListActivity;
import android.os.Bundle;
import android.view.KeyEvent;
import android.view.Menu;
import android.widget.ListView;
import java.util.ArrayList;
public class ViewList extends ListActivity {
ArrayList<Product> products = new ArrayList<Product>();
BoxAdapter boxAdapter;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
/*setContentView(R.layout.activity_view_list);*/
// создаем адаптер
fillData();
boxAdapter = new BoxAdapter(this, products);
// настраиваем список
ListView lvMain = (ListView) findViewById(R.id.lvView);
lvMain.setAdapter(boxAdapter);
}
// генерируем данные для адаптера
void fillData() {
for (int i = 1; i <= 20; i++) {
products.add(new Product("Product " + i, R.drawable.ic_launcher));
}
}
@Override
public boolean onKeyDown(int keyCode, KeyEvent event) {
if (keyCode == KeyEvent.KEYCODE_BACK) {
/*startActivity(intent);
ViewList.this.finish();
return false;*/
}
return super.onKeyDown(keyCode, event);
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.list, menu);
return true;
}
}
ERORS after setContentView
setContentView 之后的错误
08-14 09:07:53.916 52-56/system_process I/ActivityManager: Starting activity: Intent { cmp=com.shvedchenko.skleroshop/.ViewList (has extras) }
08-14 09:07:53.956 230-230/com.shvedchenko.skleroshop D/AndroidRuntime: Shutting down VM
08-14 09:07:53.956 230-230/com.shvedchenko.skleroshop W/dalvikvm: threadid=3: thread exiting with uncaught exception (group=0x4001b188)
08-14 09:07:53.956 230-230/com.shvedchenko.skleroshop E/AndroidRuntime: Uncaught handler: thread main exiting due to uncaught exception
08-14 09:07:53.966 230-230/com.shvedchenko.skleroshop E/AndroidRuntime: java.lang.RuntimeException: Unable to start activity ComponentInfo{com.shvedchenko.skleroshop/com.shvedchenko.skleroshop.ViewList}: java.lang.RuntimeException: Your content must have a ListView whose id attribute is 'android.R.id.list'
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2496)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2512)
at android.app.ActivityThread.access00(ActivityThread.java:119)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1863)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:123)
at android.app.ActivityThread.main(ActivityThread.java:4363)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:521)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:860)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:618)
at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.RuntimeException: Your content must have a ListView whose id attribute is 'android.R.id.list'
at android.app.ListActivity.onContentChanged(ListActivity.java:236)
at com.android.internal.policy.impl.PhoneWindow.setContentView(PhoneWindow.java:201)
at android.app.Activity.setContentView(Activity.java:1622)
at com.shvedchenko.skleroshop.ViewList.onCreate(ViewList.java:21)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2459)
采纳答案by yugy
If your activity extends ListActivty, your listView 's id must be "@android:id/list". You can change your activty to extends the normal Activity instead of ListActivity,or see the ListActivity document https://developer.android.com/reference/android/app/ListActivity.html
如果您的活动扩展了 ListActivty，则您的 listView 的 id 必须是“@android:id/list”。您可以更改您的活动以扩展普通活动而不是 ListActivity，或查看 ListActivity 文档https://developer.android.com/reference/android/app/ListActivity.html
回答by Goo
08-14 08:38:29.694 511-511/com.shvedchenko.skleroshop E/AndroidRuntime: java.lang.RuntimeException: Unable to start activity ComponentInfo{com.shvedchenko.skleroshop/com.shvedchenko.skleroshop.ViewList}: java.lang.NullPointerException
This stack trace probably means that an error occurs in your Activity's onCreatefunction.
此堆栈跟踪可能意味着您Activity的onCreate函数中发生错误。
You should look into this part of your code, or post it ;)
您应该查看代码的这一部分，或将其发布 ;)
回答by laalto
Call setContentView()before any of the findViewById()calls. Otherwise the Viewreturned by findViewById()will be nulland attempting to invoke a method on nullcauses NullPointerException.
setContentView()在任何调用之前findViewById()调用。否则View返回的findViewById()将是null并尝试调用null原因上的方法NullPointerException。
After fixing that you'll see
修复后你会看到
java.lang.RuntimeException: Your content must have a ListView whose id attribute is 'android.R.id.list'
This is because you're using ListActivitywhich expects to host a ListViewwith android:id="@android:id/list. To fix that, either change the idin your layout resources, or just change the activity to extend Activityinstead of ListActivity.
这是因为你使用ListActivity它预计将举办一个ListView有android:id="@android:id/list。要解决此问题，请更改id布局资源中的 ，或者只是将活动更改为扩展Activity而不是ListActivity.
回答by HpTerm
I think you simply forget to inflate your layout.
我认为您只是忘记夸大您的布局。
setContentView(R.layout.activity_view_list);
this line should not be commented orelse every call to findViewById will not work as it does not have any View inflated.
这行不应该被注释，否则每次调用 findViewById 都将不起作用，因为它没有任何视图膨胀。
