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从其他活动更新ListView

android-listview android

0

TheUnreal · 技术社区 · 10 年前

活动1: 包含ListView。

活性2: 包含更改ListView使用的SharedPreferences变量的SeekBar。更改SeekBar并返回“活动1”后,需要更新和刷新ListView。

在“活动2”更新SeekBar后,我使用以下代码返回“活动1”:

        toolbar.setNavigationIcon(R.drawable.ic_arrow_forward_white_24dp);
        toolbar.setNavigationOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
//I need to update the list here, There may be a new data!
                onBackPressed();

            }
        });

我的活动1保持未更新的相同ListView。

在更改Seekbar后,我找不到一个好的方法来刷新活动1中的列表,因为适配器仅在活动1中可用。我试图将其作为意图传递,但我注意到不可能将适配器作为附加组件传递。

有什么帮助吗?

用于更新活动1中ListView的代码:

mainListView = (ListView) findViewById(R.id.main_listview);
                    // 5. Set this activity to react to list items being pressed
                    //mainListView.setOnItemClickListener(MainActivity.this);
                    // 10. Create a JSONAdapter for the ListView
                    mJSONAdapter = new JSONAdapter(MainActivity.this, getLayoutInflater());
                    // Set the ListView to use the ArrayAdapter
                    mainListView.setAdapter(mJSONAdapter);

尝试Udi解决方案后出现Logcat错误:

08-27 12:58:29.400    1595-1595/? E/AndroidRuntimeï¹ FATAL EXCEPTION: main
    Process: il.co.test.test, PID: 1595
    java.lang.RuntimeException: Unable to resume activity {il.co.test.test/il.co.test.test.MainActivity}: java.lang.NullPointerException
            at android.app.ActivityThread.performResumeActivity(ActivityThread.java:2788)
            at android.app.ActivityThread.handleResumeActivity(ActivityThread.java:2817)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2250)
            at android.app.ActivityThread.access$800(ActivityThread.java:135)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:136)
            at android.app.ActivityThread.main(ActivityThread.java:5017)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:515)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
            at dalvik.system.NativeStart.main(Native Method)
     Caused by: java.lang.NullPointerException
            at il.co.test.test.MainActivity.onResume(MainActivity.java:334)
            at android.app.Instrumentation.callActivityOnResume(Instrumentation.java:1192)
            at android.app.Activity.performResume(Activity.java:5310)
            at android.app.ActivityThread.performResumeActivity(ActivityThread.java:2778)
Â Â Â Â Â Â Â Â Â Â Â Â at android.app.ActivityThread.handleResumeActivity(ActivityThread.java:2817)
Â Â Â Â Â Â Â Â Â Â Â Â at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2250)
Â Â Â Â Â Â Â Â Â Â Â Â at android.app.ActivityThread.access$800(ActivityThread.java:135)
Â Â Â Â Â Â Â Â Â Â Â Â at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
Â Â Â Â Â Â Â Â Â Â Â Â at android.os.Handler.dispatchMessage(Handler.java:102)
Â Â Â Â Â Â Â Â Â Â Â Â at android.os.Looper.loop(Looper.java:136)
Â Â Â Â Â Â Â Â Â Â Â Â at android.app.ActivityThread.main(ActivityThread.java:5017)
Â Â Â Â Â Â Â Â Â Â Â Â at java.lang.reflect.Method.invokeNative(Native Method)
Â Â Â Â Â Â Â Â Â Â Â Â at java.lang.reflect.Method.invoke(Method.java:515)
Â Â Â Â Â Â Â Â Â Â Â Â at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
Â Â Â Â Â Â Â Â Â Â Â Â at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
Â Â Â Â Â Â Â Â Â Â Â Â at dalvik.system.NativeStart.main(Native Method)

编辑2:完整的代码如何更新我的列表-在GPS跟踪之后。放置在MainActivity.java中。在TabFragment1.java中调用(代码如下)

public void getUpdates()
{
    // Access the device's key-value storage
    mSharedPreferences = getSharedPreferences(PREFS, MODE_PRIVATE);
    searchDistance = mSharedPreferences.getInt(PREF_DISTANCE, 0);
    if (searchDistance == 0)
        searchDistance = DEFAULT_SEARCH_DISTANCE;

        gpsDialog = new ProgressDialog(this);
        gpsDialog.setMessage("Checking your location..");
        gpsDialog.setCancelable(false);

        gpsDialog.show();

        MyLocation.LocationResult locationResult = new MyLocation.LocationResult() {
            @Override
            public void gotLocation(Location location) {
                gpsDialog.dismiss();
                //If we find a location, We will go to the list layout.
                //setContentView(R.layout.fb_list);
                // 4. Access the ListView
                mainListView = (ListView) findViewById(R.id.main_listview);
                // 5. Set this activity to react to list items being pressed
                //mainListView.setOnItemClickListener(MainActivity.this);
                // 10. Create a JSONAdapter for the ListView
                mJSONAdapter = new JSONAdapter(MainActivity.this, getLayoutInflater());
                // Set the ListView to use the ArrayAdapter
                mainListView.setAdapter(mJSONAdapter);
                double lat = location.getLatitude();
                double lon = location.getLongitude();
                query(lat, lon, searchDistance);
            }
        };
        MyLocation myLocation = new MyLocation(this);
        myLocation.getLocation(this, locationResult);
}

从片段调用此方法:

    public View onCreateView(final LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {

    final View v = inflater.inflate(R.layout.fb_list, container, false);
    MainActivity king = (MainActivity)getActivity();
    king.getUpdates();
    return v;
}

当我添加此项时:

@Override
protected void onResume() {
    super.onResume();

    //if the data has changed
    mJSONAdapter.notifyDataSetChanged();
}

应用程序由于找不到json适配器而崩溃(因为它只有在gps定位后才初始化)

3 回复 | 直到 10 年前

1

SuperFrog 10 年前

如果适配器的备份数据发生更改,则应通知适配器。在您的场景中,如果数据发生更改,您可能会考虑添加一个签入onResume方法,如果数据确实发生了更改,请通知适配器:

@Override
protected void onResume() {
    super.onResume();

    //if the data has changed
    mJSONAdapter.notifyDataSetChanged(); 
}

2

0

diyoda_ 10 年前

这只是一个空Pinter异常问题。但基本步骤如下

创建适配器并保留它。还应参考您传递到适配器中的项目列表,当您从活动2作为Udi I时,您可以清除项目列表并将新项目添加到其中(不要将项目添加为新列表,如果这样做,则必须重新实例化适配器并重置适配器)。然后呼叫 notifyDataSetChanged() 在适配器上。

编辑1:

我建议您更多地研究“活动”生命周期以及“活动”和“片段”之间的通信。我假设您在活动1中切换片段(TabFragment1)。

我不建议这样做,但你可以试试,

@Override
protected void onRestart() {
    super.onRestart();
    getUpdates();
    mainListView.setAdapter(mJSONAdapter);
}

但你必须确保,

// 10. Create a JSONAdapter for the ListView
                mJSONAdapter = new JSONAdapter(MainActivity.this, getLayoutInflater());

此mJsonAdapter不为空。

3

0

TheUnreal 10 年前

我解决了这个问题:

        toolbar.setNavigationIcon(R.drawable.ic_arrow_forward_white_24dp);
        toolbar.setNavigationOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
//I need to update the list here, There may be a new data!
                onBackPressed();

            }
        });

有了这个:

toolbar.setNavigationIcon(R.drawable.ic_arrow_forward_white_24dp);
            toolbar.setNavigationOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    Intent refresh = new Intent(Settings.this, MainActivity.class);
                    Settings.this.startActivity(refresh);
                }
            });