快速滚动时出现NullPointerException

时间:2012-12-18 16:25:16

标签: android baseadapter

我正在尝试将类别字段包含到我的Coustom ListView中。它工作正常,直到我开始快速滚动。滚动速度非常慢时,不会发生此错误。这让我很困惑。有人可以帮忙吗? 我的代码:

package com.mamlambo.tutorial.tutlist;

import java.util.ArrayList;
import java.util.TreeSet;

import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.view.View.OnClickListener;
import android.app.Activity;
import android.content.Context;
import android.content.Intent;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.widget.BaseAdapter;
import android.widget.ListView;
import android.widget.TextView;
import android.widget.ImageView;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;

public class TutListActivity extends Activity {

private DatabaseManager mHelper;
private SQLiteDatabase mDatenbank;
private ArrayList<String> devicesList;
private TreeSet<Object> mSeparatorsSet;
ListView listView;
EfficientAdapter objectAdapter;

private class EfficientAdapter extends BaseAdapter {
    private LayoutInflater mInflater;
    private Bitmap mIcon1;
    private Bitmap mIcon2;

    private static final int TYPE_ITEM = 0;
    private static final int TYPE_SEPARATOR = 1;
    private static final int TYPE_MAX_COUNT = TYPE_SEPARATOR + 1;

    public EfficientAdapter(Context context) {
        // Cache the LayoutInflate to avoid asking for a new one each time.
        mInflater = LayoutInflater.from(context);

        // Icons bound to the rows.
        mIcon1 = BitmapFactory.decodeResource(context.getResources(), R.drawable.icon);
        mIcon2 = BitmapFactory.decodeResource(context.getResources(), R.drawable.icon);
    }

    /**
     * The number of items in the list is determined by the number of speeches
     * in our array.
     *
     * @see android.widget.ListAdapter#getCount()
     */
    public int getCount() {
        return devicesList.size();
    }

    public void addItem(final String item) {
        devicesList.add(item);
        notifyDataSetChanged();
    }

    /**
     * Since the data comes from an array, just returning the index is
     * sufficent to get at the data. If we were using a more complex data
     * structure, we would return whatever object represents one row in the
     * list.
     *
     * @see android.widget.ListAdapter#getItem(int)
     */
    public Object getItem(int position) {
        return position;
    }
    /**
     * Use the array index as a unique id.
     *
     * @see android.widget.ListAdapter#getItemId(int)
     */
    public long getItemId(int position) {
        return position;
    }

    @Override
    public void notifyDataSetChanged() // Create this function in your adapter class
    {
        super.notifyDataSetChanged();
    }

    public void addSeparatorItem(final String item) {
        devicesList.add(item);
        // save separator position
        mSeparatorsSet.add(devicesList.size() - 1);
        notifyDataSetChanged();
    }

    @Override
    public int getItemViewType(int position) {
        return mSeparatorsSet.contains(position) ? TYPE_SEPARATOR : TYPE_ITEM;
    }

    public View getView(int position, View convertView, ViewGroup parent) {
        // A ViewHolder keeps references to children views to avoid unneccessary calls
        // to findViewById() on each row.
        ViewHolder holder;
        // When convertView is not null, we can reuse it directly, there is no need
        // to reinflate it. We only inflate a new View when the convertView supplied
        // by ListView is null.
        int type = getItemViewType(position);

        if (convertView == null) {

            holder = new ViewHolder();

            switch (type) {
                case TYPE_ITEM:

                    convertView = mInflater.inflate(R.layout.list_item, null);

                    holder.text = (TextView) convertView.findViewById(R.id.Title_List_Item);
                    holder.icon = (ImageView) convertView.findViewById(R.id.Delete_List_Item);

                    convertView.findViewById(R.id.Title_List_Item).setTag(devicesList.get(position));
                    convertView.findViewById(R.id.Delete_List_Item).setTag(devicesList.get(position));

                    holder.text.setText(devicesList.get(position));
                    holder.icon.setImageBitmap((position & 1) == 1 ? mIcon1 : mIcon2);

                    holder.text.setOnClickListener(mOnTitleClickListener);
                    holder.icon.setOnClickListener(mOnIconClickListener);

                    break;

                case TYPE_SEPARATOR:

                    convertView = mInflater.inflate(R.layout.seperator_item, null);

                    holder.text = (TextView)convertView.findViewById(R.id.Text_Seperator_Item);

                    holder.text.setText(devicesList.get(position));

                    break;
            }

            convertView.setTag(holder);

        } else {
            // Get the ViewHolder back to get fast access to the TextView
            // and the ImageView.
            holder = (ViewHolder) convertView.getTag();
        }
        return convertView;
    }


    private OnClickListener mOnTitleClickListener = new OnClickListener() {
        public void onClick(View v) {
                if(v.getTag().toString() == "ADD DEVICE"){
                    Intent addDevice = new Intent(getApplicationContext(), addDevice.class);
                    startActivity(addDevice);
                }else{
                    Intent showRemote = new Intent(TutListActivity.this, Remote.class);
                    showRemote.putExtra("selectedDevice", v.getTag().toString());
                    startActivity(showRemote);
                }
        }
    };

    private OnClickListener mOnIconClickListener = new OnClickListener() {
        public void onClick(View v) {
            String NameOfDevice[] = new String[2];
            NameOfDevice = v.getTag().toString().split(",");
            mDatenbank.execSQL("DELETE FROM addedDevices WHERE name = '"+NameOfDevice[0]+"'");

            ladeDevices();
            objectAdapter.notifyDataSetChanged();
        }
    };

    class ViewHolder {
        TextView text;
        ImageView icon;
    }
}


public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    setContentView(R.layout.mainlayout);

    mHelper = new DatabaseManager(this);
    mDatenbank = mHelper.getReadableDatabase();

    listView = (ListView) findViewById(R.id.list);
    objectAdapter = new EfficientAdapter(this);

    ladeDevices();
}

/*

@Override
protected void onPause() {
    super.onPause();
    mDatenbank.close();
    dataloaded = false;
}

@Override
protected void onResume() {
    super.onResume();
    mDatenbank = mHelper.getReadableDatabase();
    ladeDevices();
}

*/

private void ladeDevices() {
        devicesList = new ArrayList<String>();
        mSeparatorsSet = new TreeSet<Object>();

        Cursor devicesCursor = mDatenbank.query("addedDevices", new String[] {"name", "hersteller"}, null, null, null, null, null);
        startManagingCursor(devicesCursor);
        devicesCursor.moveToFirst();

        for (int i=0;i<devicesCursor.getCount();i++){ 
            String addingElement = new String(devicesCursor.getString(0)+", "+devicesCursor.getString(1));
            objectAdapter.addItem(addingElement);
            devicesCursor.moveToNext();
            if (i % 4 == 0) {
                objectAdapter.addSeparatorItem("separator " + i);
            }
        } 
        objectAdapter.addItem("ADD DEVICE");
        listView.setAdapter(objectAdapter);
    }

}

谢谢!

编辑: LogCat输出:

11-19 15:01:44.898: E/AndroidRuntime(957): FATAL EXCEPTION: main
11-19 15:01:44.898: E/AndroidRuntime(957): java.lang.NullPointerException
11-19 15:01:44.898: E/AndroidRuntime(957):  at com.mamlambo.tutorial.tutlist.TutListActivity$EfficientAdapter.getView(TutListActivity.java:150)
11-19 15:01:44.898: E/AndroidRuntime(957):  at android.widget.AbsListView.obtainView(AbsListView.java:2012)
11-19 15:01:44.898: E/AndroidRuntime(957):  at android.widget.ListView.makeAndAddView(ListView.java:1772)
11-19 15:01:44.898: E/AndroidRuntime(957):  at android.widget.ListView.fillUp(ListView.java:705)
11-19 15:01:44.898: E/AndroidRuntime(957):  at android.widget.ListView.correctTooHigh(ListView.java:1395)
11-19 15:01:44.898: E/AndroidRuntime(957):  at android.widget.ListView.fillGap(ListView.java:637)
11-19 15:01:44.898: E/AndroidRuntime(957):  at android.widget.AbsListView.trackMotionScroll(AbsListView.java:4546)
11-19 15:01:44.898: E/AndroidRuntime(957):  at android.widget.AbsListView.scrollIfNeeded(AbsListView.java:2852)
11-19 15:01:44.898: E/AndroidRuntime(957):  at android.widget.AbsListView.onTouchEvent(AbsListView.java:3106)
11-19 15:01:44.898: E/AndroidRuntime(957):  at android.view.View.dispatchTouchEvent(View.java:5486)
11-19 15:01:44.898: E/AndroidRuntime(957):  at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:1953)
11-19 15:01:44.898: E/AndroidRuntime(957):  at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1714)
11-19 15:01:44.898: E/AndroidRuntime(957):  at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:1959)
11-19 15:01:44.898: E/AndroidRuntime(957):  at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1728)
11-19 15:01:44.898: E/AndroidRuntime(957):  at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:1959)
11-19 15:01:44.898: E/AndroidRuntime(957):  at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1728)
11-19 15:01:44.898: E/AndroidRuntime(957):  at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:1959)
11-19 15:01:44.898: E/AndroidRuntime(957):  at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1728)
11-19 15:01:44.898: E/AndroidRuntime(957):  at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:1959)
11-19 15:01:44.898: E/AndroidRuntime(957):  at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1728)
11-19 15:01:44.898: E/AndroidRuntime(957):  at com.android.internal.policy.impl.PhoneWindow$DecorView.superDispatchTouchEvent(PhoneWindow.java:1892)
11-19 15:01:44.898: E/AndroidRuntime(957):  at com.android.internal.policy.impl.PhoneWindow.superDispatchTouchEvent(PhoneWindow.java:1371)
11-19 15:01:44.898: E/AndroidRuntime(957):  at android.app.Activity.dispatchTouchEvent(Activity.java:2364)
11-19 15:01:44.898: E/AndroidRuntime(957):  at com.android.internal.policy.impl.PhoneWindow$DecorView.dispatchTouchEvent(PhoneWindow.java:1840)
11-19 15:01:44.898: E/AndroidRuntime(957):  at android.view.View.dispatchPointerEvent(View.java:5662)
11-19 15:01:44.898: E/AndroidRuntime(957):  at android.view.ViewRootImpl.deliverPointerEvent(ViewRootImpl.java:2863)
11-19 15:01:44.898: E/AndroidRuntime(957):  at android.view.ViewRootImpl.handleMessage(ViewRootImpl.java:2442)
11-19 15:01:44.898: E/AndroidRuntime(957):  at android.os.Handler.dispatchMessage(Handler.java:99)
11-19 15:01:44.898: E/AndroidRuntime(957):  at android.os.Looper.loop(Looper.java:137)
11-19 15:01:44.898: E/AndroidRuntime(957):  at android.app.ActivityThread.main(ActivityThread.java:4340)
11-19 15:01:44.898: E/AndroidRuntime(957):  at java.lang.reflect.Method.invokeNative(Native Method)
11-19 15:01:44.898: E/AndroidRuntime(957):  at java.lang.reflect.Method.invoke(Method.java:511)
11-19 15:01:44.898: E/AndroidRuntime(957):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
11-19 15:01:44.898: E/AndroidRuntime(957):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
11-19 15:01:44.898: E/AndroidRuntime(957):  at dalvik.system.NativeStart.main(Native Method)

编辑: 我添加了一个新版本。我把listView.setAdapter(objectAdapter);在从数据库加载列表条目并将它们放入ArrayList的方法中。这样,每当某些内容发生变化(条目被删除)时,适配器都会被设置为新的。这样做允许我将setTag()和onClickListener()调用放入if(convertView == null){...},这样只有在发生变化时才会调用它们,而不是每次调用getView()时都调用它们。我认为这一定是主要的错误,虽然我不确定我的解决方案是否是一个非常好的解决方案。

1 个答案:

答案 0 :(得分:0)

声明

View view = null;

作为适配器类中的实例变量 你的其他部分看起来应该是这样的

else {
        view = convertView;
}
holder = (ViewHolder) convertView.getTag();