销毁android中的前一个片段答案

【问题标题】：Destroying previous fragment in android销毁android中的前一个片段
【发布时间】：2015-11-03 00:41:48
【问题描述】：

在我的项目中，我在其中一个片段中的 android 片段之间航行，有一个从 json 接收信息的列表。有必要每 1 分钟更新一次此列表，我正在使用

postDelayed (this, 60000);

调用一个线程，它使用 changeActivity (ActivitiesListFragment.class, null); 刷新列表。

正在运行，列表在新片段中更新。

问题是当我按下后退按钮时，它返回到上一个列表，因为它没有被“销毁”。

如何开始一个新的片段并删除之前的片段？谢谢！！

public class ActivitiesListFragment extends AbstractListFragment {
private AbstractNetworkHandler handler;
private ListView               listView;
private ActivitiesListAdapter  adapter;

private long                   currentPage   = 0L;
private int                    pageSize      = 50;
private int                    previousTotal = 0;
private boolean                loading       = true;
private boolean                isPaused;

@Override
public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable final Bundle savedInstanceState) {
    final View rootView = inflater.inflate(R.layout.fragment_activities_list, container, false);

    Handler handler;
    handler = new Handler();

    super.setupListUI(NetworkAction.ACTIVITIES_LIST, rootView, true);

    this.handler = AbstractNetworkFactory.build(super.getContext(), super.networkAction);
    this.listView = (ListView) rootView.findViewById(R.id.list_view_activities);

    this.listView.setOnScrollListener(new OnScrollListener() {
        @Override
        public void onScrollStateChanged(AbsListView view, int scrollState) {
        }

        @Override
        public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) {
            if(totalItemCount < pageSize) {
                return;
            }

            if(loading) {
                if(totalItemCount > previousTotal) {
                    loading = false;
                    previousTotal = totalItemCount;
                    currentPage++;
                }
            }
            if(!loading && (totalItemCount == (firstVisibleItem + visibleItemCount))) {
                loading = true;
                Editable text = ActivitiesListFragment.super.txtFilter.getText();
                if(text != null && text.toString() != null && !text.toString().isEmpty()) {
                    refreshGrid(text.toString(), null);
                }
                else {
                    refreshGrid(null, null);
                }
            }
        }
    });

    if(this.isPaused) {
        this.listView.setAdapter(adapter);

        Bundle arguments = getArguments();
        if(arguments != null) {
            String mode = arguments.getString("mode");
            if("search".equals(mode)) {
                Editable text = this.txtFilter.getText();

                String toFilter = text.toString();
                this.adapter.clearItems();
                this.adapter.notifyDataSetInvalidated();
                this.currentPage = 0;
                this.previousTotal = 0;

                if(toFilter != null && !toFilter.isEmpty()) {
                    refreshGrid(toFilter, null);
                }
                else {
                    refreshGrid(null, null);
                }
            }
        }
        return rootView;
    }

    if(!ApplicationOptionsManager.hasOptionsCache(super.getActivity(), networkAction)) {
        final Count c = new Count();
        // this.refreshOptions(true);// false para adicionar "Listar Todos" no
        final HomeActivity home = (HomeActivity) getActivity();

        final Runnable myRunnable= new Runnable() {
            @Override
            public void run()
            {
                refreshOptions(true);
                adapter.notifyDataSetChanged();
                handler.postDelayed(myRunnable, 60 * 1000);
            }
        };

     return rootView;
}

private void refreshOptions(final boolean isToLoad) {
    final ProgressDialog dialog = MobileUtils.getBasicProgressDialog(super.getContext());
    handler.getOptions(new HttpOptionsBaseListener() {
        @Override
        public void onRequestCompleted(OptionsVO options, Integer httpStatus, CharSequence response) {
            ApplicationOptionsManager.storeOptions(ActivitiesListFragment.super.getActivity(), networkAction, options);
            if(isToLoad) {
                String txtToFilter = txtFilter.getText().toString();

                if(txtToFilter != null && !txtToFilter.isEmpty()) {
                    refreshGrid(txtToFilter, dialog);

                }
                else {
                    refreshGrid(null, dialog);

                }
            }
            else {
                dialog.dismiss();
                // addOne(); "Listar todos" no começo do fragment
            }
        }
    }, new HttpFailListener() {
        @Override
        public void onRequestCompleted(Exception e, Integer httpStatus, CharSequence msg) {
            String txtToFilter = txtFilter.getText().toString();

            if(txtToFilter != null && !txtToFilter.isEmpty()) {
                refreshGrid(txtToFilter, null);
            }
            else {
                refreshGrid(null, null);
            }

            dialog.dismiss();
        }
    });
}

private void refreshGrid(final CharSequence textToFilter, final ProgressDialog currentDialog) {
    super.runRunnableOnUIThread(new Runnable() {
        @Override
        public void run() {
            final ProgressDialog dialog = currentDialog != null ? currentDialog : MobileUtils.getBasicProgressDialog(getContext());

            JSONObject where = new JSONObject();

            if(textToFilter != null && !textToFilter.toString().isEmpty()) {
                try {
                    where.put("nmStep", textToFilter);
                }
                catch(JSONException e) {
                }
            }

            handler.get(currentPage, new HttpJsonObjectListener() {

                @Override
                public void onRequestCompleted(final JSONObject object, Integer httpStatus, CharSequence msg) {
                    final JSONArray array = object.optJSONArray("searchResultsCollection");
                    ActivitiesListFragment.super.runRunnableOnUIThread(new Runnable() {
                        @Override
                        public void run() {
                            dialog.dismiss();

                            if(adapter != null) {
                                int count = adapter.getCount();
                                if(count > 0) {
                                    if(array.length() > 0) {
                                        adapter.addAll(array);
                                    }
                                    else {
                                        currentPage--;
                                        if(currentPage < 0) {
                                            currentPage = 0;
                                        }
                                    }
                                }
                                else {
                                    String[] columns = { "nmStep" };
                                    if(array.length() == 0) {
                                        JSONObject value = new JSONObject();

                                        try {
                                            value.put("id", -1);
                                            value.put("nmStep", "Nenhum resultado encontrado.");

                                        }
                                        catch(Exception e) {
                                        }

                                        array.put(value);
                                    }
                                    adapter = new ActivitiesListAdapter(array, columns, ActivitiesListFragment.this);
                                    listView.setAdapter(adapter);
                                }
                            }
                            else {

                                if(array.length() == 0) {
                                    JSONObject value = new JSONObject();

                                    try {
                                        value.put("id", -1);
                                        value.put("nmStep", "Nenhum resultado encontrado.");

                                    }
                                    catch(Exception e) {
                                    }

                                    array.put(value);
                                }

                                String[] columns = { "nmStep", "dtStartFmt" };
                                adapter = new ActivitiesListAdapter(array, columns, ActivitiesListFragment.this);
                                listView.setAdapter(adapter);
                            }
                        }
                    });
                }
            }, new HttpFailListener() {
                @Override
                public void onRequestCompleted(Exception e, Integer httpStatus, CharSequence msg) {
                    dialog.dismiss();
                    ActivitiesListFragment.super.runToastOnUiThread(R.string.application_generic_error, Toast.LENGTH_LONG);
                }
            });

        }
    });
}

protected int getContentViewId() {
    return(R.layout.fragment_activities_list);
}

@覆盖受保护的无效 onFilterForText(CharSequence textToFilter) { 如果（适配器！= null）{ 适配器.clearItems(); 当前页面 = 0; 上一个总计 = 0; } refreshGrid(textToFilter.toString(), null); }

@Override
protected int getTitleResource() {
    return R.string.title_activity_activities_list;
}

@Override
public void onPause() {
    handler.removeCallbacks(myRunnable);
    this.isPaused = true;
    super.onPause();
}

@Override
public void onResume() {
    handler.postDelayed(myRunnable, 60 * 1000);
    super.onResume();
}

public class Count {
    private int count;

    public int getCount() {
        return count;
    }

    public void setCount(int count) {
        this.count = count;
    }
}

public View getChildAt(int position) {
    return(this.listView.getChildAt(position));
}

}

【问题讨论】：

你使用一个activity作为两个片段之间的中间人，对吧？

标签： android android-fragments

【解决方案1】：

tiny sunlight's 帖子回答了您的问题。但是他提到，当您只想更新 ListView 时，不应该创建新的 Fragment。实际上，实现这一点的一种方法是在处理程序中更新列表的内容，而不是创建新的 Fragment。一个实现如下的 sn-p：

Handler handler;

 @Override
protected void onCreate(Bundle savedInstanceState)
{
   ....
   handler = new Handler();
}

 @Override
protected void onResume() 
{
     ....
     handler.postDelayed(myRunnable, 60 * 1000);
}

 @Override
protected void onPause() 
{
     ....
     handler.removeCallbacks(myRunnable);
}

 private final Runnable myRunnable= new Runnable() {
    @Override
    public void run()
    { 
       downloadNewJsonData();  
       adapter.notifyDataSetChanged();
       handler.postDelayed(myRunnable, 60 * 1000);
    }
 }

您从中获得的好处是避免了替换片段的内存、时间和代码开销。

【讨论】：

我正在尝试这个，但出现错误：java.lang.NullPointerException: Attempt to invoke virtual method 'void br.com.singlepoint.crm.mobile.view.list.adapter .ActivitiesListAdapter.notifyDataSetInvalidated()' 在空对象引用上
每当您导航到不同的活动并失去对当前片段的关注时，您都必须通知您的处理程序停止更新。我会编辑我的答案给你一个想法。
我试图实现，但我遇到了麻烦......如果你能看一下，我发布了我的课程的完整代码。
谢谢，我成功实现了！但是，列表会更新并与之前的列表连接，我该如何更改？
JSONArray 应该是您的活动的成员，而不是每次都在 refreshGrid 中初始化。而且您不应该在每次要更新 List 元素时都创建新的适配器。 'adapter.notifyDataSetChanged();'检查 JSONArray 成员并相应地添加/删除新元素。更多信息请查看stackoverflow.com/questions/24835969/…。

【解决方案2】：

为什么要创建一个新的Fragment 来更新？

如果你想做；像这样添加：

Fragment a = YourFragment();
getSupportFragmentManager().beginTransition().add(a,"a").commitAllowStateloss();

像这样删除：

Fragment a = getSupportFragmentManager().findFragmentWithTag("a");

if(a!=null){
getSupportFragmentManager().beginTransition().remove(a,"a").commitAllowStateloss();
}

【讨论】：

感谢小小的阳光。如何在我的班级中实现此代码？（更新了她的问题）
你的活动在哪里？