我在Android中使用ListView时遇到错误，其中填充了图片。图片网址来自tumblr JSON，android查询加载它们。我得到的错误信息是：
12-12 21:55:38.032 4334-4334/com.example.tumblrviewer E/InputEventReceiver﹕ Exception dispatching input event.
12-12 21:55:38.040 4334-4334/com.example.tumblrviewer D/dalvikvm﹕ GC_FOR_ALLOC freed 760K, 12% free 9993K/11292K, paused 5ms, total 6ms
12-12 21:55:38.040 4334-4334/com.example.tumblrviewer E/MessageQueue-JNI﹕ java.lang.NullPointerException
at com.example.tumblrviewer.MenuArrayAdapter.getView(MenuArrayAdapter.java:76)
at android.widget.AbsListView.obtainView(AbsListView.java:2161)
at android.widget.ListView.makeAndAddView(ListView.java:1840)
at android.widget.ListView.fillDown(ListView.java:675)
at android.widget.ListView.fillGap(ListView.java:639)
at android.widget.AbsListView.trackMotionScroll(AbsListView.java:4970)
at android.widget.AbsListView.onGenericMotionEvent(AbsListView.java:3680)
at android.view.View.dispatchGenericMotionEventInternal(View.java:7479)
at android.view.View.dispatchGenericMotionEvent(View.java:7460)
at android.view.ViewGroup.dispatchTransformedGenericPointerEvent(ViewGroup.java:1819)
at android.view.ViewGroup.dispatchGenericPointerEvent(ViewGroup.java:1772)
at android.view.View.dispatchGenericMotionEvent(View.java:7453)
at android.view.ViewGroup.dispatchTransformedGenericPointerEvent(ViewGroup.java:1819)
at android.view.ViewGroup.dispatchGenericPointerEvent(ViewGroup.java:1772)
at android.view.View.dispatchGenericMotionEvent(View.java:7453)
at android.view.ViewGroup.dispatchTransformedGenericPointerEvent(ViewGroup.java:1819)
at android.view.ViewGroup.dispatchGenericPointerEvent(ViewGroup.java:1772)
at android.view.View.dispatchGenericMotionEvent(View.java:7453)
at android.view.ViewGroup.dispatchTransformedGenericPointerEvent(ViewGroup.java:1819)
at android.view.ViewGroup.dispatchGenericPointerEvent(ViewGroup.java:1772)
at android.view.View.dispatchGenericMotionEvent(View.java:7453)
at com.android.internal.policy.impl.PhoneWindow$DecorView.superDispatchGenericMotionEvent(PhoneWindow.java:1974)
at com.android.internal.policy.impl.PhoneWindow.superDispatchGenericMotionEvent(PhoneWindow.java:1428)
at android.app.Activity.dispatchGenericMotionEvent(Activity.java:2460)
at com.android.internal.policy.impl.PhoneWindow$DecorView.dispatchGenericMotionEvent(PhoneWindow.java:1928)
at android.view.View.dispatchPointerEvent(View.java:7566)
at android.view.ViewRootImpl$ViewPostImeInputStage.processPointerEvent(ViewRootImpl.java:3883)
at android.view.ViewRootImpl$ViewPostImeInputStage.onProcess(ViewRootImpl.java:3778)
at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:3379)
at android.view.ViewRootImpl$InputStage.onDeliverToNext(ViewRootImpl.java:3429)
at android.view.ViewRootImpl$InputStage.forward(ViewRootImpl.java:3398)
at android.view.ViewRootImpl$AsyncInputStage.forward(ViewRootImpl.java:3483)
at android.view.ViewRootImpl$InputStage.apply(ViewRootImpl.java:3406)
at android.view.ViewRootImpl$AsyncInputStage.apply(ViewRootImpl.java:3540)
at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:3379)
at android.view.ViewRootImpl$InputStage.onDeliverToNext(ViewRootImpl.java:3429)
at android.view.ViewRootImpl$InputStage.forward(ViewRootImpl.java:3398)
at android.view.ViewRootImpl$InputStage.apply(ViewRootImpl.java:3406)
at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:3379)
at android.view.ViewRootImpl.deliverInputEvent(ViewRootImpl.java:5419)
at android.view.ViewRootImpl.doProcessInputEvents(ViewRootImpl.java:5399)
at android.view.ViewRootImpl.enqueueInputEvent(ViewRootImpl.java:5370)
at android.view.ViewRootImpl$WindowInputEventReceiver.onInputEvent(ViewRootImpl.java:5493)
at android.view.InputEventReceiver.dispatchInputEvent(InputEventReceiver.java:182)
at android.os.MessageQueue.nativePollOnce(Native Method)
at android.os.MessageQueue.next(MessageQueue.java:132)
at android.os.Looper.loop(Looper.java:124)
at android.app.ActivityThread.main(ActivityThread.java:5103)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:525)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
at dalvik.system.NativeStart.main(Native Method)
12-12 21:55:38.044 4334-4334/com.example.tumblrviewer D/AndroidRuntime﹕ Shutting down VM
12-12 21:55:38.044 4334-4334/com.example.tumblrviewer W/dalvikvm﹕ threadid=1: thread exiting with uncaught exception (group=0xa4bd3648)
12-12 21:55:38.052 4334-4334/com.example.tumblrviewer E/AndroidRuntime﹕ FATAL EXCEPTION: main
java.lang.NullPointerException
at com.example.tumblrviewer.MenuArrayAdapter.getView(MenuArrayAdapter.java:76)
at android.widget.AbsListView.obtainView(AbsListView.java:2161)
at android.widget.ListView.makeAndAddView(ListView.java:1840)
at android.widget.ListView.fillDown(ListView.java:675)
at android.widget.ListView.fillGap(ListView.java:639)
at android.widget.AbsListView.trackMotionScroll(AbsListView.java:4970)
at android.widget.AbsListView.onGenericMotionEvent(AbsListView.java:3680)
at android.view.View.dispatchGenericMotionEventInternal(View.java:7479)
at android.view.View.dispatchGenericMotionEvent(View.java:7460)
at android.view.ViewGroup.dispatchTransformedGenericPointerEvent(ViewGroup.java:1819)
at android.view.ViewGroup.dispatchGenericPointerEvent(ViewGroup.java:1772)
at android.view.View.dispatchGenericMotionEvent(View.java:7453)
at android.view.ViewGroup.dispatchTransformedGenericPointerEvent(ViewGroup.java:1819)
at android.view.ViewGroup.dispatchGenericPointerEvent(ViewGroup.java:1772)
at android.view.View.dispatchGenericMotionEvent(View.java:7453)
at android.view.ViewGroup.dispatchTransformedGenericPointerEvent(ViewGroup.java:1819)
at android.view.ViewGroup.dispatchGenericPointerEvent(ViewGroup.java:1772)
at android.view.View.dispatchGenericMotionEvent(View.java:7453)
at android.view.ViewGroup.dispatchTransformedGenericPointerEvent(ViewGroup.java:1819)
at android.view.ViewGroup.dispatchGenericPointerEvent(ViewGroup.java:1772)
at android.view.View.dispatchGenericMotionEvent(View.java:7453)
at com.android.internal.policy.impl.PhoneWindow$DecorView.superDispatchGenericMotionEvent(PhoneWindow.java:1974)
at com.android.internal.policy.impl.PhoneWindow.superDispatchGenericMotionEvent(PhoneWindow.java:1428)
at android.app.Activity.dispatchGenericMotionEvent(Activity.java:2460)
at com.android.internal.policy.impl.PhoneWindow$DecorView.dispatchGenericMotionEvent(PhoneWindow.java:1928)
at android.view.View.dispatchPointerEvent(View.java:7566)
at android.view.ViewRootImpl$ViewPostImeInputStage.processPointerEvent(ViewRootImpl.java:3883)
at android.view.ViewRootImpl$ViewPostImeInputStage.onProcess(ViewRootImpl.java:3778)
at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:3379)
at android.view.ViewRootImpl$InputStage.onDeliverToNext(ViewRootImpl.java:3429)
at android.view.ViewRootImpl$InputStage.forward(ViewRootImpl.java:3398)
at android.view.ViewRootImpl$AsyncInputStage.forward(ViewRootImpl.java:3483)
at android.view.ViewRootImpl$InputStage.apply(ViewRootImpl.java:3406)
at android.view.ViewRootImpl$AsyncInputStage.apply(ViewRootImpl.java:3540)
at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:3379)
at android.view.ViewRootImpl$InputStage.onDeliverToNext(ViewRootImpl.java:3429)
at android.view.ViewRootImpl$InputStage.forward(ViewRootImpl.java:3398)
at android.view.ViewRootImpl$InputStage.apply(ViewRootImpl.java:3406)
at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:3379)
at android.view.ViewRootImpl.deliverInputEvent(ViewRootImpl.java:5419)
at android.view.ViewRootImpl.doProcessInputEvents(ViewRootImpl.java:5399)
at android.view.ViewRootImpl.enqueueInputEvent(ViewRootImpl.java:5370)
at android.view.ViewRootImpl$WindowInputEventReceiver.onInputEvent(ViewRootImpl.java:5493)
at android.view.InputEventReceiver.dispatchInputEvent(InputEventReceiver.java:182)
at android.os.MessageQueue.nativePollOnce(Native Method)
at android.os.MessageQueue.next(MessageQueue.java:132)
at android.os.Looper.loop(Looper.java:124)
at android.app.ActivityThread.main(ActivityThread.java:5103)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:525)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
at dalvik.system.NativeStart.main(Native Method)
它指向MenuArrayAdapter第76行，其中包含：
mAQ.id(viewHolder.mImageView).image(item.photos[0].photoUrl.uri, false, false, 600, 0, null, Constants.FADE_IN);
我很确定这个对象不是null，因为错误是随机发生的，每次都在ArrayAdapter中使用不同的项。当我快速，上下滚动ListView时会发生这种情况。我看到图像没有时间加载。它可能与内存问题有关吗？内存和应用程序崩溃的数据太多了？如果是这样，那么什么是一个好的解决方案，如果我想保持无限滚动 - 我不想在底部添加“加载更多”按钮，例如Instagram没有这样的按钮，它可以加载大量的图像。
该类的完整代码如下：
package com.example.tumblrviewer;
import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.ImageView;
import com.androidquery.AQuery;
import com.androidquery.callback.AjaxCallback;
import com.androidquery.callback.AjaxStatus;
import com.androidquery.util.Constants;
import com.example.tumblrviewer.model.HomeResponse;
import com.example.tumblrviewer.model.Item;
import org.json.JSONException;
import org.json.JSONObject;
public class MenuArrayAdapter extends ArrayAdapter<Item> {
private final LayoutInflater mInflater;
private final int mResourceId;
private AQuery mAQ;
private int postOffset;
public MenuArrayAdapter(Context context, int resource) {
super(context, resource);
mInflater = LayoutInflater.from(context);
mResourceId = resource;
mAQ = new AQuery(context);
postOffset=0;
//loadImages(postOffset);
}
public void setPosts(Item[] posts) {
//clear();
for (Item item : posts) {
add(item);
}
if (isEmpty()) {
notifyDataSetInvalidated();
} else {
notifyDataSetChanged();
}
}
@Override
public View getView(int i, View convertView, ViewGroup viewGroup) {
ViewHolder viewHolder = null;
if (convertView == null) {
viewHolder = new ViewHolder();
convertView = mInflater.inflate(mResourceId, viewGroup, false);
viewHolder.mImageView = (ImageView) convertView.findViewById(R.id.tumblr_photo_iv);
//viewHolder.mTagsLayout=(LinearLayout) convertView.findViewById(R.id.tags_layout);
convertView.setTag(viewHolder);
} else {
viewHolder = (ViewHolder) convertView.getTag();
}
Item item = getItem(i);
//if ( item.photos[0].photoUrl.uri != null) {
mAQ.id(viewHolder.mImageView).image(item.photos[0].photoUrl.uri, false, false, 600, 0, null, Constants.FADE_IN);
//}
return convertView;
}
private class ViewHolder {
ImageView mImageView;
//LinearLayout mTagsLayout;
}
}
还有主要活动
package com.example.tumblrviewer;
import android.app.Activity;
import android.os.Bundle;
import android.widget.AbsListView;
import android.widget.ListView;
import android.widget.TextView;
import android.widget.Toast;
import com.androidquery.AQuery;
import com.androidquery.callback.AjaxCallback;
import com.androidquery.callback.AjaxStatus;
import com.example.tumblrviewer.model.HomeResponse;
import org.json.JSONException;
import org.json.JSONObject;
public class WeHaveTheMunchiesActivity extends Activity {
private AQuery mAQ;
private TextView mResultTextView;
private ListView mListView;
private MenuArrayAdapter mItemArrayAdapter;
private int postOffset;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_list_viewer);
mListView = (ListView) findViewById(R.id.items_lv);
mAQ = new AQuery(this);
mItemArrayAdapter = new MenuArrayAdapter(this, R.layout.item_on_list);
mListView.setAdapter(mItemArrayAdapter);
postOffset=0;
loadImages(postOffset);
mListView.setOnScrollListener(new AbsListView.OnScrollListener() {
@Override
public void onScrollStateChanged(AbsListView absListView, int i) {
}
@Override
public void onScroll(AbsListView absListView, int firstVisibleItem, int visibleItemCount, int totalItemCount) {
int lastItem = firstVisibleItem + visibleItemCount;
if(lastItem == totalItemCount ){
if(postOffset <= 10662
&& mListView.getChildAt(mListView.getChildCount() - 1) != null
&& mListView.getLastVisiblePosition() == mListView.getAdapter().getCount() - 1
&& mListView.getChildAt(mListView.getChildCount() - 1).getBottom() <= mListView.getHeight()) {
Toast.makeText(getApplicationContext(), "Bottom!", Toast.LENGTH_LONG).show();
loadImages(postOffset);
System.out.println("postOffset "+postOffset);
}
}
}
});
}
private void loadImages(int offset) {
String url = Constants.TUMBLR_API_BLOG_URL + Constants.TUMBLR_API_BLOG_HOSTNAME +
Constants.TUMBLR_API_CONTENT_TYPE + Constants.TUMBLR_API_KEY_NAME +
Constants.TUMBLR_API_KEY + "&offset=" + Integer.toString(offset);
AjaxCallback<JSONObject> cb = new AjaxCallback<JSONObject>();
cb.url(url).type(JSONObject.class).weakHandler(this, "itemsCallback");
mAQ.ajax(cb);
postOffset=postOffset+20;
}
public void itemsCallback(String url, JSONObject json, AjaxStatus status) throws JSONException {
//Toast.makeText(getApplicationContext(), status.getRedirect(), Toast.LENGTH_LONG).show();
//Toast.makeText(getApplicationContext(), status.getCode(), Toast.LENGTH_LONG).show();
//mResultTextView.setText(status.getMessage());
if (json != null) {
HomeResponse homeResponse = HomeResponse.fromJsonObject(json.getJSONObject("response"));
System.out.print(homeResponse.items);
mItemArrayAdapter.setPosts(homeResponse.items);
}
}
}