java - 根据列表项的位置替换 fragment

Question

我的 fragment 使用 2 行 ListView 。如何根据所选 ListView 项目的位置执行必要的程序？下面是替换详细信息 fragment 的代码，但它与位置无关。

• 如果 mTwoPane 为 true，我希望将详细信息容器替换为 fragment (使用该列表项中的 fragment 名称)
• 如果 mTwoPane 为 false，我希望启动该 Activity (使用该列表项中的 Activity 名称)

更换详细信息容器

                FragmentLineChooserList newFragment = new FragmentLineChooserList();
                FragmentTransaction transaction = FragmentMainList.this.getActivity().getSupportFragmentManager().beginTransaction();
                transaction.replace(R.id.detail_container, newFragment);
                transaction.commit();

FragmentWCLine.java

public class FragmentWCLine extends android.support.v4.app.Fragment {

    ListView listView;

    private class WC {
        private CharSequence station;
        private CharSequence zone;
        private Class<? extends Activity> activityClass;
        private Class<? extends android.support.v4.app.Fragment> fragmentClass;

        public WC(int stationResId, int zoneResId, Class<? extends Activity> activityClass, Class<? extends android.support.v4.app.Fragment> fragmentClass) {
            this.fragmentClass = fragmentClass;
            this.activityClass = activityClass;
            this.station = getResources().getString(stationResId);
            this.zone = getResources().getString(zoneResId);
        }

        @Override
        public String toString() { return station.toString(); }
        public String getzone(){ return zone.toString(); }
    }

    private static WC[] mWC;

    private boolean mTwoPane;

    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState){
        View v = inflater.inflate(R.layout.fragment_wc_line, container, false);

        mWC = new WC[]{
                new WC(R.string.bank, R.string.zone_1, WCBankActivity.class, FragmentWCBank.class),
                new WC(R.string.wat, R.string.zone_1, WCWATActivity.class, FragmentWCWAT.class)
        };

        listView = (ListView)v.findViewById(R.id.list_wc);
        listView.setAdapter(new MyAdapter(getActivity(), mWC));

        listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
                if (mTwoPane) {
                    startActivity(new Intent(getActivity(), mWC[position].fragmentClass));
                } else {
                    startActivity(new Intent(getActivity(), mWC[position].activityClass));
                }
            }
        });

        return v;
    }

    static class MyAdapter extends BaseAdapter {

        static class ViewHolder {
            TextView station;
            TextView zone;
        }

        LayoutInflater inflater;
        WC[] mWC;

        public MyAdapter(Context contexts, WC[] samples) {
            this.mWC = samples;
            inflater = LayoutInflater.from(contexts);
        }

        @Override
        public int getCount() {
            return mWC.length;
        }

        @Override
        public Object getItem(int position) {
            return mWC[position];
        }

        @Override
        public long getItemId(int position) {
            return 0;
        }

        @Override
        public View getView(int position, View convertView, ViewGroup parent) {
            ViewHolder viewHolder;
            if (convertView == null) {
                convertView = inflater.inflate(R.layout.list_item_dualline, null);
                viewHolder = new ViewHolder();

                viewHolder.station = (TextView) convertView.findViewById(R.id.list_item_station);
                viewHolder.zone = (TextView) convertView.findViewById(R.id.list_item_zone);
                convertView.setTag(viewHolder);
            } else {
                viewHolder = (ViewHolder) convertView.getTag();
            }
            viewHolder.station.setText(mWC[position].station);
            viewHolder.zone.setText(mWC[position].getzone());
            return convertView;
        }
    }
}

FragmentWCLine - 更新 0

public class FragmentWCLine extends android.support.v4.app.Fragment {

    ListView listView;

    private class WC {
        private CharSequence station;
        private CharSequence zone;
        private Class<? extends Activity> activityClass;
        private Class<? extends android.support.v4.app.Fragment> fragmentClass;

        public WC(int stationResId, int zoneResId, Class<? extends Activity> activityClass, Class<? extends android.support.v4.app.Fragment> fragmentClass) {
            this.fragmentClass = fragmentClass;
            this.activityClass = activityClass;
            this.station = getResources().getString(stationResId);
            this.zone = getResources().getString(zoneResId);
        }

        @Override
        public String toString() { return station.toString(); }
        public String getzone(){ return zone.toString(); }
    }

    private static WC[] mWC;

    private boolean mTwoPane;

    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState){
        View v = inflater.inflate(R.layout.fragment_wc_line, container, false);

        mWC = new WC[]{
                new WC(R.string.bank, R.string.zone_1, WCBankActivity.class, FragmentWCBank.class),
                new WC(R.string.wat, R.string.zone_1, WCWATActivity.class, FragmentWCWAT.class)
        };

        listView = (ListView)v.findViewById(R.id.list_wc);
        listView.setAdapter(new MyAdapter(getActivity(), mWC));

        listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
                if (mTwoPane) {
                    startActivity(new Intent(getActivity(), mWC[position].fragmentClass));
                } else {
                    startActivity(new Intent(getActivity(), mWC[position].activityClass));
                }
            }
        });

        return v;
    }

    static class MyAdapter extends BaseAdapter {

        static class ViewHolder {
            TextView station;
            TextView zone;
        }

        LayoutInflater inflater;
        WC[] mWC;

        public MyAdapter(Context contexts, WC[] samples) {
            this.mWC = samples;

        }

        @Override
        public int getCount() {
            return mWC.length;
        }

        @Override
        public Object getItem(int position) {
            return mWC[position];
        }



        public View getView(int position, View convertView, ViewGroup parent) {
            ViewHolder viewHolder;
            if (convertView == null) {
                convertView = inflater.inflate(R.layout.list_item_dualline, null);
                viewHolder = new ViewHolder();

                viewHolder.station = (TextView) convertView.findViewById(R.id.list_item_station);
                viewHolder.zone = (TextView) convertView.findViewById(R.id.list_item_zone);
                convertView.setTag(viewHolder);
            } else {
                viewHolder = (ViewHolder) convertView.getTag();
            }
            viewHolder.station.setText(mWC[position].station);
            viewHolder.zone.setText(mWC[position].getzone());
            return convertView;
        }
    }
}

FragmentWCLine - 更新 1

public class FragmentWCLine extends android.support.v4.app.Fragment {
ListView listView;

private class WC {
    private CharSequence station;
    private CharSequence zone;
    private Class<? extends Activity> activityClass;
    private Class<? extends android.support.v4.app.Fragment> fragmentClass;

    public WC(int stationResId, int zoneResId, Class<? extends Activity> activityClass, Class<? extends android.support.v4.app.Fragment> fragmentClass) {
        this.fragmentClass = fragmentClass;
        this.activityClass = activityClass;
        this.station = getResources().getString(stationResId);
        this.zone = getResources().getString(zoneResId);

    }

    @Override
    public String toString() { return station.toString(); }
    public String getzone(){ return zone.toString(); }
}

private static WC[] mWC;

private boolean mTwoPane;

public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState){
    View v = inflater.inflate(R.layout.fragment_wc_line, container, false);

    mWC = new WC[]{
            new WC(R.string.bank, R.string.zone_1, WCBankActivity.class, FragmentWCBank.class),
            new WC(R.string.wat, R.string.zone_1, WCWATActivity.class, FragmentWCWAT.class)
    };

    listView = (ListView)v.findViewById(R.id.list_wc);
    listView.setAdapter(new MyAdapter(getActivity(), mWC));

    listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
        @Override
        public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
            if (mTwoPane) {
                startActivity(new Intent(getActivity(), mWC[position].fragmentClass));
            } else {
                startActivity(new Intent(getActivity(), mWC[position].activityClass));
            }
        }
    });

    return v;
}

static class MyAdapter extends BaseAdapter {

    static class ViewHolder {
        TextView station;
        TextView zone;
    }

    LayoutInflater inflater;
    WC[] mWC;

    public MyAdapter(Context contexts, WC[] samples) {
        this.mWC = samples;

    }

    @Override
    public int getCount() {
        return mWC.length;
    }

    @Override
    public Object getItem(int position) {
        return mWC[position];
    }

    @Override
    public long getItemId(int position) {
        return position;
    }


    public View getView(int position, View convertView, ViewGroup parent) {
        ViewHolder viewHolder;
        if (convertView == null) {
            convertView = inflater.inflate(R.layout.list_item_dualline, null);
            viewHolder = new ViewHolder();

            viewHolder.station = (TextView) convertView.findViewById(R.id.list_item_station);
            viewHolder.zone = (TextView) convertView.findViewById(R.id.list_item_zone);
            convertView.setTag(viewHolder);
        } else {
            viewHolder = (ViewHolder) convertView.getTag();
        }
        viewHolder.station.setText(mWC[position].station);
        viewHolder.zone.setText(mWC[position].getzone());
        return convertView;
    }
}
}

Answer 1

我注意到 MyAdapter 构造函数中的代码 inflater = LayoutInflater.from(contexts) 存在一个问题。它不应该驻留在这个方法中。我从未见过任何示例项目在构造函数中执行此操作。原因是如果用户翻转手机或 Android 决定换出您的应用程序以释放内存，则构造函数不会恢复。测试一下。

代码建议，在getView中膨胀:

public View getView(int position, View convertView, ViewGroup parent) {
   if (convertView == null) {
      convertView = LayoutInflater.from(contexts).inflate(R.layout.list_item_dualline, null);
...
}

新代码建议:

@Override
    public long getItemId(int position) {
        return position;
    }

注释:

• 从构造函数获取上下文并将其保存到 getView()。
• 我注意到您定义了 getItemId() 并在适配器中返回 0，而不是实际值(如位置或 mWC[position] 的成员变量)。如果此方法返回 0 或 null，则引用它的任何代码都会与零值混淆。
• getItemId 的代码是从 ArrayAdapter 中的同一方法复制的。