Android ListView扩展BaseAdapter在活动启动时崩溃
[英]Android ListView Extending BaseAdapter Crashes on Activity Launch
问题描述
I have an listview as sidebar in my MainActivity. 
我的MainActivity中有一个作为边栏的列表视图。 I wanted to set an listview item color to a custom color in onCreate(). 我想在onCreate（）中将listview项目颜色设置为自定义颜色。 So i am using an BaseAdapter and overriding its view . 所以我正在使用BaseAdapter并覆盖其视图。 And i am setting listview to an ArrayAdapter. 我将listview设置为ArrayAdapter。 But my App crashed on Launch. 但是我的应用在启动时崩溃了。 Can anybody plz help me with this. 有人可以帮助我吗？
This is my MainActivity code 这是我的MainActivity代码
import java.util.ArrayList;
import android.os.Bundle;
import android.app.Activity;
import android.content.Intent;
import android.view.Menu;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ListView;
public class MainActivity extends Activity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
ListView listview=(ListView)findViewById(R.id.listView);
ArrayList<String > list = new ArrayList<String>();
list.add("sohail");
list.add("aziz");
list.add("hassan");
CustomAdapter adapter=new CustomAdapter(this,list);
listview.setAdapter(adapter);
listview.setOnItemClickListener(new AdapterView.OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> parent, View view,
int position, long id) {
// Show Alert
}
});
}
@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;
}
}
This is the Base Adapter in which i am overriding my view. 这是我要覆盖其视图的基本适配器。
import android.content.Context;
import android.graphics.Color;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import java.util.ArrayList;
/**
* Created by polak_000 on 10/2/13.
*/
public class CustomAdapter extends BaseAdapter{
Context mycontext;
ArrayList<String> contactsList;
LayoutInflater minflater;
public CustomAdapter(Context context, ArrayList<String> list)
{
this.mycontext=context;
contactsList=list;
minflater =LayoutInflater.from(context);
}
@Override
public int getCount()
{
return contactsList.size();
}
@Override
public Object getItem(int position)
{
return contactsList.get(position);
}
@Override
public long getItemId(int position) {
// TODO Auto-generated method stub
return position;
}
@Override
public View getView(int position,View convertView,ViewGroup parent)
{
if (convertView !=null)
{
if (position ==1)
{
convertView.setBackgroundColor(Color.BLUE);
}
}
return convertView;
}
}
And This is my Layout for MainActivity. 这是我的MainActivity布局。
<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"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context=".MainActivity" >
<ListView
android:id="@+id/listView"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center"
android:background="@android:color/holo_green_light"
android:minHeight="50dp"
/>
</RelativeLayout>
And this is my Catlog 这是我的目录
10-02 14:11:22.125: D/AndroidRuntime(2036): Shutting down VM 10-02 14:11:22.125: W/dalvikvm(2036): threadid=1: thread exiting with uncaught exception (group=0x41465700) 10-02 14:11:22.215: D/dalvikvm(2036): GC_FOR_ALLOC freed 80K, 5% free 2940K/3072K, paused 34ms, total 36ms 10-02 14:11:22.225: E/AndroidRuntime(2036): FATAL EXCEPTION: main 10-02 14:11:22.225: E/AndroidRuntime(2036): java.lang.NullPointerException 10-02 14:11:22.225: E/AndroidRuntime(2036): at android.widget.AbsListView.obtainView(AbsListView.java:2179) 10-02 14:11:22.225: E/AndroidRuntime(2036): at android.widget.ListView.measureHeightOfChildren(ListView.java:1247) 10-02 14:11:22.225: E/AndroidRuntime(2036): at android.widget.ListView.onMeasure(ListView.java:1159) 10-02 14:11:22.225: E/AndroidRuntime(2036): at android.view.View.measure(View.java:15848) 10-02 14:11:22.225: E/AndroidRuntime(2036): at android.widget.RelativeLayout.measureChildHorizontal(RelativeLayout.java:728) 10-02 14:11:22.225: E/AndroidRuntime(2036):
4 个解决方案
解决方案1
0 2013-10-02 19:06:40
You are returning a null from getView function in the adapter. 您正在从适配器的getView函数返回null。 You need to make sure that you are implementing getView function as per your need. 您需要确保根据需要实现getView函数。 Here is a guide on how to do it : http://www.androidhive.info/2011/10/android-listview-tutorial/ 这是有关操作方法的指南： http : //www.androidhive.info/2011/10/android-listview-tutorial/
解决方案2
0 2013-10-02 20:11:35
More clearly, you need to create the view in getView(). 更清楚地说，您需要在getView（）中创建视图。
Something like: 就像是：
public View getView(int position, View convertView, ViewGroup parent) {
try {
View v = convertView;
if (v == null) {
v = layoutInflater.inflate(R.layout.yadda_yadda, null);
}
...
}
解决方案3
0 2013-10-03 04:25:36
// try this
1. list item layout **list_item.xml**
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:id="@+id/lnrListItem"
android:layout_width="match_parent"
android:padding="5dp"
android:layout_height="wrap_content">
<TextView
android:id="@+id/textview"
android:layout_width="wrap_content"
android:layout_height="wrap_content"/>
</LinearLayout>
2. list adapter
public class CustomAdapter extends BaseAdapter {
Context mycontext;
ArrayList<String> contactsList;
LayoutInflater minflater;
public CustomAdapter(Context context, ArrayList<String> list)
{
this.mycontext=context;
contactsList=list;
minflater =LayoutInflater.from(context);
}
@Override
public int getCount()
{
return contactsList.size();
}
@Override
public Object getItem(int position)
{
return contactsList.get(position);
}
@Override
public long getItemId(int position) {
// TODO Auto-generated method stub
return position;
}
@Override
public View getView(int position,View convertView,ViewGroup parent)
{
ViewHolder holder;
if (convertView == null)
{
holder = new ViewHolder();
convertView = LayoutInflater.from(mycontext).inflate(R.layout.list_item,null,false);
holder.lnrListItem = (LinearLayout) convertView.findViewById(R.id.lnrListItem);
holder.textView = (TextView) convertView.findViewById(R.id.textview);
convertView.setTag(holder);
}else{
holder = (ViewHolder)convertView.getTag();
}
if ((position%2)==0)
{
holder.lnrListItem.setBackgroundColor(Color.CYAN); // odd item background are cyan
}else{
holder.lnrListItem.setBackgroundColor(Color.BLUE); // even item background are blue
}
holder.textView.setText(contactsList.get(position));
return convertView;
}
class ViewHolder{
LinearLayout lnrListItem;
TextView textView;
}
}
解决方案4
0 2013-10-03 05:50:16
If you want to create custom view for your listview then you have to set the custom layout in your getView() method using LayoutInflater and return that view in getView() method then only you will be able to set the color on that view. 如果要为列表视图创建自定义视图，则必须使用LayoutInflater在getView（）方法中设置自定义布局，然后在getView()方法中返回该视图，那么只有您才能在该视图上设置颜色。 Otherwise getView will always retrun null in convertView . 否则，getView将始终在convertView null。 Try as below in your getView() method. 在您的getView()方法中尝试以下操作。
@Override public View getView(int position,View convertView,ViewGroup parent) { ViewHolder holder; View m_view=convertView ; if (convertView == null) { holder = new ViewHolder(); m_view= LayoutInflater.from(mycontext).inflate(R.layout.list_item,null,false); holder.item= (LinearLayout) m_view.findViewById(R.id.lnrListItem); holder.textView = (TextView) m_view.findViewById(R.id.textview); m_view.setTag(holder); }else{ holder = (ViewHolder)m_view.getTag(); } if (position==1) { holder.item.setBackgroundColor(Color.CYAN); }else{ holder.item.setBackgroundColor(Color.BLUE); } holder.textView.setText(contactsList.get(position)); return m_view; } class ViewHolder{ LinearLayout item; TextView textView; }
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