[英]Updating ListView from another Activity
活動1:包含ListView。
Acitivity 2:包含SeekBar,它可以更改ListView使用的SharedPreferences變量。 更改SeekBar並返回到活動1后,需要更新和刷新ListView。
在活動2中更新SeekBar之后,我使用以下代碼返回活動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();
}
});
我的活動1保持未更新的相同ListView。
更改Seekbar之后,我找不到在活動1中刷新列表的好方法,因為適配器僅在活動1中可用。我試圖將其作為意圖進行傳遞,但我注意到無法將適配器作為附加傳遞。
有什么幫助嗎?
我在活動1中用於更新ListView的代碼:
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);
嘗試Udi解決方案后出現Logcat錯誤:
08-27 12:58:29.400 1595-1595/? E/AndroidRuntime﹕ 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)
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)
編輯2:完整代碼如何在GPS跟蹤后更新我的列表。 放在MainActivity.java中。 在TabFragment1.java中調用(下面的代碼)
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);
}
從片段中調用此方法:
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;
}
當我添加此:
@Override
protected void onResume() {
super.onResume();
//if the data has changed
mJSONAdapter.notifyDataSetChanged();
}
應用程序崩潰,因為它找不到json適配器(因為僅在gps位置之后才初始化)
如果adapater的后備數據已更改,則應通知適配器。 在您的方案中,您可能會考慮在onResume方法中添加一個檢查,如果數據已更改,並且如果確實更改了,則通知適配器:
@Override
protected void onResume() {
super.onResume();
//if the data has changed
mJSONAdapter.notifyDataSetChanged();
}
這只是一個空品特例外問題。 但是基本步驟如下
創建適配器並保留它。 還保留對傳遞給適配器的項目列表的引用,當您從活動2來時,作為Udi我可以清除項目列表並向其中添加新項目(不要將項目添加為新列表) ,如果這樣做,則必須重新實例化適配器並重置適配器)。 然后在適配器上調用notifyDataSetChanged()
。
編輯1:
我建議您更多地研究“活動”生命周期以及“活動”和“片段”之間的通信。 我假設您在活動1中切換片段(TabFragment1)。
我不建議這樣做,但是您可以嘗試一下,
@Override
protected void onRestart() {
super.onRestart();
getUpdates();
mainListView.setAdapter(mJSONAdapter);
}
但是您必須確保
// 10. Create a JSONAdapter for the ListView
mJSONAdapter = new JSONAdapter(MainActivity.this, getLayoutInflater());
此mJsonAdapter不為null。
我通過替換它解決了這個問題:
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();
}
});
有了這個:
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);
}
});
聲明:本站的技術帖子網頁,遵循CC BY-SA 4.0協議,如果您需要轉載,請注明本站網址或者原文地址。任何問題請咨詢:yoyou2525@163.com.