Question

有人可以帮我解决我的问题。我仍在尝试使用DraggingListView和ArrayAdapter。现在我想通过点击来实现listview中的删除元素，但是当我做的时候：

StableArrayAdapter.this.notifyDataSetChanged();

我得到nullPointer Exception ...

这是我的适配器：

public class StableArrayAdapter extends ArrayAdapter<Product> {

    final int INVALID_ID = -1;
    LayoutInflater lInflater;
    Context ctx;
    public static final String PREFS_NAME = "com.shvedchenko.skleroshop";
    public static final String PREFS_THEME = "theme";

    HashMap<Product, Integer> mIdMap = new HashMap<Product, Integer>();

    public StableArrayAdapter(Context context, int textViewResourceId, List<Product> prod) {
        super(context, textViewResourceId, /*objects*/prod);
        lInflater = (LayoutInflater) context
                .getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        ctx = context;
        for (int i = 0; i < prod.size(); ++i) {
            mIdMap.put(prod.get(i), i);
        }
    }


    // пункт списка
    @Override
    public View getView(final int position, View convertView, final ViewGroup parent) {
        // используем созданные, но не используемые view
        View view = convertView;
        if (view == null) {
            view = lInflater.inflate(R.layout.item, parent, false);
        }

        Product p = getItem(position);

        SharedPreferences pref = ctx.getSharedPreferences(PREFS_NAME, ctx.MODE_PRIVATE);
        int theme = pref.getInt(PREFS_THEME, 0);             // getting Integer

        if(theme == 0)
            ((TextView) view.findViewById(R.id.tvDescr)).setTextColor(Color.WHITE);
        else
            ((TextView) view.findViewById(R.id.tvDescr)).setTextColor(Color.BLACK);

        ((TextView) view.findViewById(R.id.tvDescr)).setText(p.getProductName());
        ((ImageView) view.findViewById(R.id.ivImage)).setImageResource(p.getProductImage());

        ImageView iv = (ImageView)view.findViewById(R.id.ivImage);
        iv.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                mIdMap.remove(getItem(position));
                System.out.println("FROM CLICK -- " + mIdMap.size() );
                /*for( Product p : mIdMap.keySet() ) {
                    System.out.println( p.getProductName() );
                }*/
                //StableArrayAdapter.this.notifyDataSetChanged();
            }
        });

        return view;
    }

    /*@Override
    public Object getItem(int position) {
        return mIdMap.get(position);
    }*/


    @Override
    public long getItemId(int position) {
        if (position < 0 || position >= mIdMap.size()) {
            return INVALID_ID;
        }
        Product item = (Product) getItem(position);
        return mIdMap.get(item);
    }

    @Override
    public boolean hasStableIds() {
        return true;
    }

}

这是错误：

08-26 08：50：58.902 2167-2167 / com.shvedchenko.skleroshop E / AndroidRuntime：致命异常：主要显示java.lang.NullPointerException 在com.shvedchenko.skleroshop.StableArrayAdapter.getItemId（StableArrayAdapter.java:104）在android.widget.AdapterView.rememberSyncState（AdapterView.java:1195）在android.widget.AdapterView $ AdapterDataSetObserver.onChanged（AdapterView.java:810）在android.widget.AbsListView $ AdapterDataSetObserver.onChanged（AbsListView.java:5958）在android.database.DataSetObservable.notifyChanged（DataSetObservable.java:37）在android.widget.BaseAdapter.notifyDataSetChanged（BaseAdapter.java:50）在android.widget.ArrayAdapter.notifyDataSetChanged（ArrayAdapter.java:286）在com.shvedchenko.skleroshop.StableArrayAdapter $ 1.onClick（StableArrayAdapter.java:85）在android.view.View.performClick（View.java:4204）在android.view.View $ PerformClick.run（View.java:17355）在android.os.Handler.handleCallback（Handler.java:725）在android.os.Handler.dispatchMessage（Handler.java:92）在android.os.Looper.loop（Looper.java:137）在android.app.ActivityThread.main（ActivityThread.java:5041） at java.lang.reflect.Method.invokeNative（Native Method）在java.lang.reflect.Method.invoke（Method.java:511）在com.android.internal.os.ZygoteInit $ MethodAndArgsCaller.run（ZygoteInit.java:793）在com.android.internal.os.ZygoteInit.main（ZygoteInit.java:560）在dalvik.system.NativeStart.main（本地方法）

/ 已更新 /

我的适配器现在：

public class StableArrayAdapter extends ArrayAdapter<Product> {

    final int INVALID_ID = -1;
    LayoutInflater lInflater;
    Context ctx;
    public static final String PREFS_NAME = "com.shvedchenko.skleroshop";
    public static final String PREFS_THEME = "theme";

    HashMap<Product, Integer> mIdMap = new HashMap<Product, Integer>();
    ArrayList<Product> prods = new ArrayList<Product>();

    public StableArrayAdapter(Context context, int textViewResourceId, List<Product> prod) {
        super(context, textViewResourceId, /*objects*/prod);
        lInflater = (LayoutInflater) context
                .getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        ctx = context;
        for (int i = 0; i < prod.size(); ++i) {
            mIdMap.put(prod.get(i), i);
            prods.add(i,prod.get(i));
        }
    }


    // пункт списка
    @Override
    public View getView(final int position, View convertView, final ViewGroup parent) {
        // используем созданные, но не используемые view
        View view = convertView;
        if (view == null) {
            view = lInflater.inflate(R.layout.item, parent, false);
        }

        Product p = getItem(position);

        SharedPreferences pref = ctx.getSharedPreferences(PREFS_NAME, ctx.MODE_PRIVATE);
        int theme = pref.getInt(PREFS_THEME, 0);             // getting Integer

        if(theme == 0)
            ((TextView) view.findViewById(R.id.tvDescr)).setTextColor(Color.WHITE);
        else
            ((TextView) view.findViewById(R.id.tvDescr)).setTextColor(Color.BLACK);

        ((TextView) view.findViewById(R.id.tvDescr)).setText(p.getProductName());
        ((ImageView) view.findViewById(R.id.ivImage)).setImageResource(p.getProductImage());

        ImageView iv = (ImageView)view.findViewById(R.id.ivImage);
        iv.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                prods.remove(position);
                StableArrayAdapter.this.notifyData(prods);

            }
        });

        return view;
    }

    public void notifyData(List<Product> prod) {

        //First of all Clear Map
        mIdMap.clear();
        for (int i = 0; i < prod.size(); ++i) {
            mIdMap.put(prod.get(i), i);
        }

        notifyDataSetChanged();
    }


    @Override
    public long getItemId(int position) {
        if (position < 0 || position >= mIdMap.size()) {
            return INVALID_ID;
        }
        Product item = (Product) getItem(position);
        return mIdMap.get(item);
    }

    @Override
    public boolean hasStableIds() {
        return true;
    }

}

/ ERROR /

08-26 09:53:19.270 2530-2530 / com.shvedchenko.skleroshop E / AndroidRuntime：致命例外：主要显示java.lang.NullPointerException 在com.shvedchenko.skleroshop.StableArrayAdapter.getItemId（StableArrayAdapter.java:122）在android.widget.AdapterView.rememberSyncState（AdapterView.java:1195）在android.widget.AdapterView $ AdapterDataSetObserver.onChanged（AdapterView.java:810）在android.widget.AbsListView $ AdapterDataSetObserver.onChanged（AbsListView.java:5958）在android.database.DataSetObservable.notifyChanged（DataSetObservable.java:37）在android.widget.BaseAdapter.notifyDataSetChanged（BaseAdapter.java:50）在android.widget.ArrayAdapter.notifyDataSetChanged（ArrayAdapter.java:286）在com.shvedchenko.skleroshop.StableArrayAdapter.notifyData（StableArrayAdapter.java:112）在com.shvedchenko.skleroshop.StableArrayAdapter $ 1.onClick（StableArrayAdapter.java:91）

我做错了什么？

TNX提前！

Answer 1

正确的适配器代码：

public class StableArrayAdapter extends ArrayAdapter<Product> {

    final int INVALID_ID = -1;
    LayoutInflater lInflater;
    Context ctx;
    public static final String PREFS_NAME = "com.shvedchenko.skleroshop";
    public static final String PREFS_THEME = "theme";

    HashMap<Product, Integer> mIdMap = new HashMap<Product, Integer>();

    public StableArrayAdapter(Context context, int textViewResourceId, List<Product> prod) {
        super(context, textViewResourceId, /*objects*/prod);
        lInflater = (LayoutInflater) context
                .getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        ctx = context;
        for (int i = 0; i < prod.size(); i++) {
            mIdMap.put(prod.get(i), i);
        }
    }


    // пункт списка
    @Override
    public View getView(final int position, View convertView, final ViewGroup parent) {
        // используем созданные, но не используемые view
        View view = convertView;
        if (view == null) {
            view = lInflater.inflate(R.layout.item, parent, false);
        }

        Product p = getItem(position);

        SharedPreferences pref = ctx.getSharedPreferences(PREFS_NAME, ctx.MODE_PRIVATE);
        int theme = pref.getInt(PREFS_THEME, 0);             // getting Integer

        if(theme == 0)
            ((TextView) view.findViewById(R.id.tvDescr)).setTextColor(Color.WHITE);
        else
            ((TextView) view.findViewById(R.id.tvDescr)).setTextColor(Color.BLACK);

        ((TextView) view.findViewById(R.id.tvDescr)).setText(p.getProductName());
        ((ImageView) view.findViewById(R.id.ivImage)).setImageResource(p.getProductImage());

        ImageView iv = (ImageView)view.findViewById(R.id.ivImage);
        iv.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                StableArrayAdapter.this.remove(getItem(position));
                StableArrayAdapter.this.notifyDataSetChanged();
            }
        });

        return view;
    }


    @Override
    public long getItemId(int position) {
        if (position < 0 || position >= mIdMap.size()) {
            return INVALID_ID;
        }
        Product item = (Product) getItem(position);
        return mIdMap.get(item);
    }

    @Override
    public boolean hasStableIds() {
        return true;
    }

}

Answer 2

从列表中删除项目

  list.remove(position);

然后使用适配器对象调用以下方法。

  stableAdapter.notifyData(list);

在Adapter类中编写一个方法。

  public void notifyData(List<Product> prod)
  {

      //First of all Clear Map
      mIdMap.clear();
      for (int i = 0; i < prod.size(); ++i) {
          mIdMap.put(prod.get(i), i);
      }   

      notifyDataSetChanged();
  }

使用adpater对象

调用此方法

Android - 自定义ArrayAdapter

2 个答案: