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Android set listview addapter空异常

android exception listview

Android set listview addapter空异常,android,exception,listview,null,Android,Exception,Listview,Null,我需要找到一种方法将ListView addapter设置为null。我想这样做的原因是，我在Tab中有4个子活动，其中每个活动都是延迟加载列表。在活动的OnDestroy方法中，我执行以下操作： @Override public void onDestroy() { adapter.imageLoader.stopThread(); listView.setAdapter(null); super.onDestroy(); } 但当我这样做时，我得到了一个例外： 08

我需要找到一种方法将ListView addapter设置为null。我想这样做的原因是，我在Tab中有4个子活动，其中每个活动都是延迟加载列表。在活动的OnDestroy方法中，我执行以下操作：

@Override
public void onDestroy()
{
    adapter.imageLoader.stopThread();
    listView.setAdapter(null);
    super.onDestroy();
}
但当我这样做时，我得到了一个例外：

08-13 15:29:43.115: ERROR/AndroidRuntime(10381): FATAL EXCEPTION: main
08-13 15:29:43.115: ERROR/AndroidRuntime(10381): java.lang.RuntimeException: Unable to destroy activity {com.stampii.stampii/com.stampii.stampii.mystampii.OwnedStampii}: java.lang.NullPointerException
08-13 15:29:43.115: ERROR/AndroidRuntime(10381):     at android.app.ActivityThread.performDestroyActivity(ActivityThread.java:3874)
08-13 15:29:43.115: ERROR/AndroidRuntime(10381):     at android.app.ActivityThread.performDestroyActivity(ActivityThread.java:3784)
08-13 15:29:43.115: ERROR/AndroidRuntime(10381):     at android.app.LocalActivityManager.performDestroy(LocalActivityManager.java:355)
08-13 15:29:43.115: ERROR/AndroidRuntime(10381):     at android.app.LocalActivityManager.destroyActivity(LocalActivityManager.java:381)
08-13 15:29:43.115: ERROR/AndroidRuntime(10381):     at com.stampii.stampii.TabGroupActivity.finishFromChild(TabGroupActivity.java:46)
08-13 15:29:43.115: ERROR/AndroidRuntime(10381):     at android.app.Activity.finish(Activity.java:3290)
08-13 15:29:43.115: ERROR/AndroidRuntime(10381):     at com.stampii.stampii.mystampii.OwnedStampii$1.onClick(OwnedStampii.java:38)
08-13 15:29:43.115: ERROR/AndroidRuntime(10381):     at android.view.View.performClick(View.java:2408)
08-13 15:29:43.115: ERROR/AndroidRuntime(10381):     at android.view.View$PerformClick.run(View.java:8817)
08-13 15:29:43.115: ERROR/AndroidRuntime(10381):     at android.os.Handler.handleCallback(Handler.java:587)
08-13 15:29:43.115: ERROR/AndroidRuntime(10381):     at android.os.Handler.dispatchMessage(Handler.java:92)
08-13 15:29:43.115: ERROR/AndroidRuntime(10381):     at android.os.Looper.loop(Looper.java:144)
08-13 15:29:43.115: ERROR/AndroidRuntime(10381):     at android.app.ActivityThread.main(ActivityThread.java:4937)
08-13 15:29:43.115: ERROR/AndroidRuntime(10381):     at java.lang.reflect.Method.invokeNative(Native Method)
08-13 15:29:43.115: ERROR/AndroidRuntime(10381):     at java.lang.reflect.Method.invoke(Method.java:521)
08-13 15:29:43.115: ERROR/AndroidRuntime(10381):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
08-13 15:29:43.115: ERROR/AndroidRuntime(10381):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
08-13 15:29:43.115: ERROR/AndroidRuntime(10381):     at dalvik.system.NativeStart.main(Native Method)
08-13 15:29:43.115: ERROR/AndroidRuntime(10381): Caused by: java.lang.NullPointerException
08-13 15:29:43.115: ERROR/AndroidRuntime(10381):     at com.stampii.stampii.mystampii.OwnedStampii.onDestroy(OwnedStampii.java:102)
08-13 15:29:43.115: ERROR/AndroidRuntime(10381):     at android.app.ActivityThread.performDestroyActivity(ActivityThread.java:3861)
在第102行我有这样一个：
listView.setAdapter（null）

如果删除该代码，我会得到：


08-13 15:33:36.545: ERROR/AndroidRuntime(10511): FATAL EXCEPTION: main
08-13 15:33:36.545: ERROR/AndroidRuntime(10511): java.lang.ArrayIndexOutOfBoundsException: Array index out of range: 0
08-13 15:33:36.545: ERROR/AndroidRuntime(10511):     at java.util.Vector.elementAt(Vector.java:329)
08-13 15:33:36.545: ERROR/AndroidRuntime(10511):     at java.util.Vector.get(Vector.java:443)
08-13 15:33:36.545: ERROR/AndroidRuntime(10511):     at com.stampii.stampii.tableview.ImageLoader$PhotosQueue.Clean(ImageLoader.java:126)
08-13 15:33:36.545: ERROR/AndroidRuntime(10511):     at com.stampii.stampii.tableview.ImageLoader.queuePhoto(ImageLoader.java:59)
08-13 15:33:36.545: ERROR/AndroidRuntime(10511):     at com.stampii.stampii.tableview.ImageLoader.DisplayImage(ImageLoader.java:51)
08-13 15:33:36.545: ERROR/AndroidRuntime(10511):     at com.stampii.stampii.tableview.LazyAdapter.getView(LazyAdapter.java:62)
08-13 15:33:36.545: ERROR/AndroidRuntime(10511):     at android.widget.AbsListView.obtainView(AbsListView.java:1294)
08-13 15:33:36.545: ERROR/AndroidRuntime(10511):     at android.widget.ListView.measureHeightOfChildren(ListView.java:1198)
08-13 15:33:36.545: ERROR/AndroidRuntime(10511):     at android.widget.ListView.onMeasure(ListView.java:1109)
08-13 15:33:36.545: ERROR/AndroidRuntime(10511):     at android.view.View.measure(View.java:8172)
08-13 15:33:36.545: ERROR/AndroidRuntime(10511):     at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:3140)
08-13 15:33:36.545: ERROR/AndroidRuntime(10511):     at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1012)
08-13 15:33:36.545: ERROR/AndroidRuntime(10511):     at android.widget.LinearLayout.measureVertical(LinearLayout.java:381)
08-13 15:33:36.545: ERROR/AndroidRuntime(10511):     at android.widget.LinearLayout.onMeasure(LinearLayout.java:304)
08-13 15:33:36.545: ERROR/AndroidRuntime(10511):     at android.view.View.measure(View.java:8172)
08-13 15:33:36.545: ERROR/AndroidRuntime(10511):     at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:3140)
08-13 15:33:36.545: ERROR/AndroidRuntime(10511):     at android.widget.FrameLayout.onMeasure(FrameLayout.java:245)
08-13 15:33:36.545: ERROR/AndroidRuntime(10511):     at android.view.View.measure(View.java:8172)
08-13 15:33:36.545: ERROR/AndroidRuntime(10511):     at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:3140)
08-13 15:33:36.545: ERROR/AndroidRuntime(10511):     at android.widget.FrameLayout.onMeasure(FrameLayout.java:245)
08-13 15:33:36.545: ERROR/AndroidRuntime(10511):     at android.view.View.measure(View.java:8172)
08-13 15:33:36.545: ERROR/AndroidRuntime(10511):     at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:3140)
08-13 15:33:36.545: ERROR/AndroidRuntime(10511):     at android.widget.FrameLayout.onMeasure(FrameLayout.java:245)
08-13 15:33:36.545: ERROR/AndroidRuntime(10511):     at android.view.View.measure(View.java:8172)
08-13 15:33:36.545: ERROR/AndroidRuntime(10511):     at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:3140)
08-13 15:33:36.545: ERROR/AndroidRuntime(10511):     at android.widget.FrameLayout.onMeasure(FrameLayout.java:245)
08-13 15:33:36.545: ERROR/AndroidRuntime(10511):     at android.view.View.measure(View.java:8172)
08-13 15:33:36.545: ERROR/AndroidRuntime(10511):     at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:3140)
08-13 15:33:36.545: ERROR/AndroidRuntime(10511):     at android.widget.FrameLayout.onMeasure(FrameLayout.java:245)
08-13 15:33:36.545: ERROR/AndroidRuntime(10511):     at android.view.View.measure(View.java:8172)
08-13 15:33:36.545: ERROR/AndroidRuntime(10511):     at android.widget.LinearLayout.measureVertical(LinearLayout.java:521)
08-13 15:33:36.545: ERROR/AndroidRuntime(10511):     at android.widget.LinearLayout.onMeasure(LinearLayout.java:304)
08-13 15:33:36.545: ERROR/AndroidRuntime(10511):     at android.view.View.measure(View.java:8172)
08-13 15:33:36.545: ERROR/AndroidRuntime(10511):     at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:3140)
08-13 15:33:36.545: ERROR/AndroidRuntime(10511):     at android.widget.FrameLayout.onMeasure(FrameLayout.java:245)
08-13 15:33:36.545: ERROR/AndroidRuntime(10511):     at android.view.View.measure(View.java:8172)
08-13 15:33:36.545: ERROR/AndroidRuntime(10511):     at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:3140)
08-13 15:33:36.545: ERROR/AndroidRuntime(10511):     at android.widget.FrameLayout.onMeasure(FrameLayout.java:245)
08-13 15:33:36.545: ERROR/AndroidRuntime(10511):     at android.view.View.measure(View.java:8172)
08-13 15:33:36.545: ERROR/AndroidRuntime(10511):     at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:3140)
08-13 15:33:36.545: ERROR/AndroidRuntime(10511):     at android.widget.FrameLayout.onMeasure(FrameLayout.java:245)
08-13 15:33:36.545: ERROR/AndroidRuntime(10511):     at android.view.View.measure(View.java:8172)
08-13 15:33:36.545: ERROR/AndroidRuntime(10511):     at android.view.ViewRoot.performTraversals(ViewRoot.java:805)
08-13 15:33:36.545: ERROR/AndroidRuntime(10511):     at android.view.ViewRoot.handleMessage(ViewRoot.java:1744)
08-13 15:33:36.545: ERROR/AndroidRuntime(10511):     at android.os.Handler.dispatchMessage(Handler.java:99)
08-13 15:33:36.545: ERROR/AndroidRuntime(10511):     at android.os.Looper.loop(Looper.java:144)
08-13 15:33:36.545: ERROR/AndroidRuntime(10511):     at android.app.ActivityThread.main(ActivityThread.java:4937)
08-13 15:33:36.545: ERROR/AndroidRuntime(10511):     at java.lang.reflect.Method.invokeNative(Native Method)
08-13 15:33:36.545: ERROR/AndroidRuntime(10511):     at java.lang.reflect.Method.invoke(Method.java:521)
08-13 15:33:36.545: ERROR/AndroidRuntime(10511):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
08-13 15:33:36.545: ERROR/AndroidRuntime(10511):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
08-13 15:33:36.545: ERROR/AndroidRuntime(10511):     at dalvik.system.NativeStart.main(Native Method)


下面是ImageLoader.class：


package com.stampii.stampii.tableview;

import java.io.File;
import java.io.InputStream;
import java.util.HashMap;
import java.util.Stack;
import javax.crypto.Cipher;
import javax.crypto.CipherInputStream;
import javax.crypto.spec.IvParameterSpec;
import javax.crypto.spec.SecretKeySpec;
import com.stampii.stampii.R;
import android.app.Activity;
import android.content.Context;
import android.content.res.AssetManager;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.util.Log;
import android.widget.ImageView;

public class ImageLoader extends Activity {

    //the simplest in-memory cache implementation. This should be replaced with something like SoftReference or BitmapOptions.inPurgeable(since 1.6)
    private HashMap<String, Bitmap> cache=new HashMap<String, Bitmap>();

    private File cacheDir;
    private AssetManager mAssetManager;


    public ImageLoader(Context context){
        //Make the background thead low priority. This way it will not affect the UI performance
        photoLoaderThread.setPriority(Thread.NORM_PRIORITY-1);
        mAssetManager = context.getAssets();

        //Find the dir to save cached images
        if (android.os.Environment.getExternalStorageState().equals(android.os.Environment.MEDIA_MOUNTED))
            cacheDir=new File(android.os.Environment.getExternalStorageDirectory(),"LazyList");
        else
            cacheDir=context.getCacheDir();
        if(!cacheDir.exists())
            cacheDir.mkdirs();
    }


    final int stub_id=R.drawable.default_img;
    public void DisplayImage(String url, Activity activity, ImageView imageView)
    {
        if(cache.containsKey(url))
            imageView.setImageBitmap(cache.get(url));
        else
        {
            queuePhoto(url, activity, imageView);
            imageView.setImageResource(stub_id);
        }    
    }

    private void queuePhoto(String url, Activity activity, ImageView imageView)
    {
        //This ImageView may be used for other images before. So there may be some old tasks in the queue. We need to discard them. 
        photosQueue.Clean(imageView);
        PhotoToLoad p=new PhotoToLoad(url, imageView);
        synchronized(photosQueue.photosToLoad){
            photosQueue.photosToLoad.push(p);
            photosQueue.photosToLoad.notifyAll();
        }

        //start thread if it's not started yet
        if(photoLoaderThread.getState()==Thread.State.NEW)
            photoLoaderThread.start();
    }

    private Bitmap getBitmap(String src) {
        Bitmap myBitmap = null;


                //Decryption
                try {
                Cipher cipher = Cipher.getInstance("AES/CBC/NoPadding");
                SecretKeySpec keySpec = new SecretKeySpec("01234567890abcde".getBytes(), "AES");
                IvParameterSpec ivSpec = new IvParameterSpec("fedcba9876543210".getBytes());
                cipher.init(Cipher.DECRYPT_MODE, keySpec, ivSpec);

                InputStream input = mAssetManager.open(src);
                CipherInputStream cis = new CipherInputStream(input, cipher);

                myBitmap = BitmapFactory.decodeStream(cis);

                }
                catch(Exception e){
                    e.printStackTrace();
                    Log.v("ERROR","Error : "+e);
                }


                return myBitmap;


        }

    //Task for the queue
    private class PhotoToLoad
    {
        public String url;
        public ImageView imageView;
        public PhotoToLoad(String u, ImageView i){
            url=u; 
            imageView=i;
        }
    }

    PhotosQueue photosQueue=new PhotosQueue();

    public void stopThread()
    {
        photoLoaderThread.interrupt();
    }

    //stores list of photos to download
    class PhotosQueue
    {
        private Stack<PhotoToLoad> photosToLoad=new Stack<PhotoToLoad>();

        //removes all instances of this ImageView
        public void Clean(ImageView image)
        {
            for(int j=0 ;j<photosToLoad.size();){
                if(photosToLoad.get(j).imageView==image)
                    photosToLoad.remove(j);
                else
                    ++j;
            }
        }
    }

    class PhotosLoader extends Thread {
        public void run() {
            try {
                while(true)
                {
                    //thread waits until there are any images to load in the queue
                    if(photosQueue.photosToLoad.size()==0)
                        synchronized(photosQueue.photosToLoad){
                            photosQueue.photosToLoad.wait();
                        }
                    if(photosQueue.photosToLoad.size()!=0)
                    {
                        PhotoToLoad photoToLoad;
                        synchronized(photosQueue.photosToLoad){
                            photoToLoad=photosQueue.photosToLoad.pop();
                        }
                        Bitmap bmp=getBitmap(photoToLoad.url);
                        cache.put(photoToLoad.url, bmp);
                        Object tag=photoToLoad.imageView.getTag();
                        if(tag!=null && ((String)tag).equals(photoToLoad.url)){
                            BitmapDisplayer bd=new BitmapDisplayer(bmp, photoToLoad.imageView);
                            Activity a=(Activity)photoToLoad.imageView.getContext();
                            a.runOnUiThread(bd);
                        }
                    }
                    if(Thread.interrupted())
                        break;
                }
            } catch (InterruptedException e) {
                //allow thread to exit
            }
        }
    }

    PhotosLoader photoLoaderThread=new PhotosLoader();

    //Used to display bitmap in the UI thread
    class BitmapDisplayer implements Runnable
    {
        Bitmap bitmap;
        ImageView imageView;
        public BitmapDisplayer(Bitmap b, ImageView i){bitmap=b;imageView=i;}
        public void run()
        {
            if(bitmap!=null)
                imageView.setImageBitmap(bitmap);
            else
                imageView.setImageResource(stub_id);
        }
    }

    public void clearCache() {
        //clear memory cache

        long size=0;
            cache.clear();

            //clear SD cache
            File[] files=cacheDir.listFiles();
            for(File f:files){
                size=size+f.length();
                    f.delete();
            }
}




}



package com.stampii.stampii.tableview；
导入java.io.File；
导入java.io.InputStream；
导入java.util.HashMap；
导入java.util.Stack；
导入javax.crypto.Cipher；
导入javax.crypto.cipheriputstream；
导入javax.crypto.spec.IvParameterSpec；
导入javax.crypto.spec.SecretKeySpec；
进口com.stampii.stampii.R；
导入android.app.Activity；
导入android.content.Context；
导入android.content.res.AssetManager；
导入android.graphics.Bitmap；
导入android.graphics.BitmapFactory；
导入android.util.Log；
导入android.widget.ImageView；
公共类ImageLoader扩展活动{
//最简单的内存缓存实现。应该用SoftReference或BitmapOptions.Inpurgable（自1.6起）之类的东西来代替
私有HashMap缓存=新建HashMap（）；
私有文件cacheDir；
私人资产管理公司mAssetManager；
公共图像加载器（上下文）{
//将后台设为低优先级。这样不会影响UI性能
photoLoaderThread.setPriority（Thread.NORM_PRIORITY-1）；
mAssetManager=context.getAssets（）；
//查找目录以保存缓存的图像
if（android.os.Environment.getExternalStorageState（）.equals（android.os.Environment.MEDIA_-MOUNTED））
cacheDir=新文件（android.os.Environment.getExternalStorageDirectory（），“LazyList”）；
其他的
cacheDir=context.getCacheDir（）；
如果（！cacheDir.exists（））
cacheDir.mkdirs（）；
}
最终int stub\u id=R.drawable.default\u img；
public void DisplayImage（字符串url、活动活动、图像视图）
{
if（cache.containsKey（url））
setImageBitmap（cache.get（url））；
其他的
{
队列照片（url、活动、图像视图）；
setImageResource（存根id）；
}    
}
私有void queuePhoto（字符串url、活动活动、ImageView ImageView）
{
//此ImageView以前可能用于其他图像。因此队列中可能有一些旧任务。我们需要丢弃它们。
Photosque.Clean（imageView）；
PhotoToLoad p=新的PhotoToLoad（url，imageView）；
已同步（PhotoQueue.photosToLoad）{
photoqueue.photoload.push（p）；
photoqueue.phototoload.notifyAll（）；
}
//如果尚未启动，则启动线程
if（photoLoaderThread.getState（）==Thread.State.NEW）
photoLoaderThread.start（）；
}
私有位图getBitmap（字符串src）{
位图myBitmap=null；
//解密
试一试{
Cipher Cipher=Cipher.getInstance（“AES/CBC/NoPadding”）；
SecretKeySpec keySpec=新的SecretKeySpec（“01234567890abcde”.getBytes（），“AES”）；
IvParameterSpec ivSpec=新的IvParameterSpec（“fedcba9876543210.getBytes（））；
cipher.init（cipher.DECRYPT_模式，keySpec，ivSpec）；
InputStream输入=mAssetManager.open（src）；
CipherInputStream cis=新的CipherInputStream（输入，密码）；
myBitmap=BitmapFactory.decodeStream（cis）；
}
捕获（例外e）{
e、 printStackTrace（）；
Log.v（“错误”，“错误：+e”）；
}
返回我的位图；
}
//队列的任务
私有类光电负载
{
公共字符串url；
公共影像视图；
公共PhotoToLoad（字符串u，图像视图i）{
url=u；
imageView=i；
}
}
PhotosQueue PhotosQueue=新的PhotosQueue（）；
公共void stopThread（）
{
photoLoaderThread.interrupt（）；
}
//存储要下载的照片列表
类队列
{
私有堆栈photoload=新堆栈（）；
//删除此ImageView的所有实例
公共空间清理（图像视图图像）
{

对于（int j=0；j您指定
null
作为适配器。这不是一个有效的适配器，当然会抛出
NullPointerException
来强调这一点


另一个例外很难从这一小段代码中看出。请再发布一些。
不是100%确定，但据我所知，您没有
onCreate（）
函数或任何设置布局的地方（通过
setContentView（）
）对于这个活动。但是你必须设置一个。异常基本上告诉你的是listview不能测量它应该有多大，因为它不能确定其他UI组件的大小以及它们消耗了多少空间。因为没有。实际上它不是一个活动，我忘了删除extends活动，这就是为什么我没有nCreate方法。基本上是第二个例外，每次我在4个具有惰性列表的活动之间更改20或30次时都会遇到。在我删除extends活动后，我没有得到它。所以现在还可以。感谢您的通知。我如何设置listview大小？通常最好的方法是通过
android:l在XML布局中设置它ayout_width
和
android:layout_height
属性。在代码中也应该可以，但根据我的经验，这很快就会变得难看。实际上，这些参数是为列表视图设置的。这很好，只是想指出，这是更改大小的最佳位置。我相信你必须首先设置这些参数。