多個DatePicker，當屏幕旋轉時強制關閉

Question

這是我的第一個Android應用程序，在此之前我根本沒有Java知識。

我使用了下面的代碼（found in another question，作者：Adam L.），我有28個時間選擇器，它在修改了代碼後效果很好。
但我注意到的一件事是，當我處於timepickerdialog（或使用此處顯示的代碼的datepickerdialog）時，我得到了強制關閉（nullpointerexception）並更改了屏幕的方向。
我想我需要用onDestroy保存一些信息並用onStart重新恢復它，但我不知道如何完成此操作。
在我自己的代碼中，我使用了timepickerdialogs，但是Adam L.的代碼更加清晰，所以解決那裏的問題也會解決我自己的問題。

import java.util.Calendar; 
import android.app.Activity; 
import android.app.DatePickerDialog; 
import android.app.Dialog; 
import android.app.DatePickerDialog.OnDateSetListener; 
import android.os.Bundle; 
import android.view.View; 
import android.widget.Button; 
import android.widget.DatePicker; 
import android.widget.TextView; 

public class MultiDatePickerActivity extends Activity { 

private TextView startDateDisplay; 
private TextView endDateDisplay; 
private Button startPickDate; 
private Button endPickDate; 
private Calendar startDate; 
private Calendar endDate; 

static final int DATE_DIALOG_ID = 0; 

private TextView activeDateDisplay; 
private Calendar activeDate; 

protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.multidatepicker); 

    /* capture our View elements for the start date function */ 
    startDateDisplay = (TextView) findViewById(R.id.startDateDisplay); 
    startPickDate = (Button) findViewById(R.id.startPickDate); 

    /* get the current date */ 
    startDate = Calendar.getInstance(); 

    /* add a click listener to the button */ 
    startPickDate.setOnClickListener(new View.OnClickListener() { 
     public void onClick(View v) { 
      showDateDialog(startDateDisplay, startDate); 
     } 
    }); 

    /* capture our View elements for the end date function */ 
    endDateDisplay = (TextView) findViewById(R.id.endDateDisplay); 
    endPickDate = (Button) findViewById(R.id.endPickDate); 

    /* get the current date */ 
    endDate = Calendar.getInstance(); 

    /* add a click listener to the button */ 
    endPickDate.setOnClickListener(new View.OnClickListener() { 
     public void onClick(View v) { 
      showDateDialog(endDateDisplay, endDate); 
     } 
    }); 

    /* display the current date (this method is below) */ 
    updateDisplay(startDateDisplay, startDate); 
    updateDisplay(endDateDisplay, endDate); 
} 

private void updateDisplay(TextView dateDisplay, Calendar date) { 
    dateDisplay.setText(
      new StringBuilder() 
       // Month is 0 based so add 1 
       .append(date.get(Calendar.MONTH) + 1).append("-") 
       .append(date.get(Calendar.DAY_OF_MONTH)).append("-") 
       .append(date.get(Calendar.YEAR)).append(" ")); 

} 

public void showDateDialog(TextView dateDisplay, Calendar date) { 
    activeDateDisplay = dateDisplay; 
    activeDate = date; 
    showDialog(DATE_DIALOG_ID); 
} 

private OnDateSetListener dateSetListener = new OnDateSetListener() { 
    @Override 
    public void onDateSet(DatePicker view, int year, int monthOfYear, int dayOfMonth) { 
     activeDate.set(Calendar.YEAR, year); 
     activeDate.set(Calendar.MONTH, monthOfYear); 
     activeDate.set(Calendar.DAY_OF_MONTH, dayOfMonth); 
     updateDisplay(activeDateDisplay, activeDate); 
     unregisterDateDisplay(); 
    } 
}; 

private void unregisterDateDisplay() { 
    activeDateDisplay = null; 
    activeDate = null; 
} 

@Override 
protected Dialog onCreateDialog(int id) { 
    switch (id) { 
     case DATE_DIALOG_ID: 
      return new DatePickerDialog(this, dateSetListener, activeDate.get(Calendar.YEAR), activeDate.get(Calendar.MONTH), activeDate.get(Calendar.DAY_OF_MONTH)); 
    } 
    return null; 
} 

@Override 
protected void onPrepareDialog(int id, Dialog dialog) { 
    super.onPrepareDialog(id, dialog); 
    switch (id) { 
     case DATE_DIALOG_ID: 
      ((DatePickerDialog) dialog).updateDate(activeDate.get(Calendar.YEAR), activeDate.get(Calendar.MONTH), activeDate.get(Calendar.DAY_OF_MONTH)); 
      break; 
    } 
} 
} 

我覺得這是logcat的Eclipse中有趣的部分：

12-18 11:32:52.415: INFO/ActivityManager(577): Displayed activity se.bergsland.manydatepickers/.ManyDatePickers: 993 ms 
12-18 11:32:57.625: DEBUG/dalvikvm(1734): GC freed 1950 objects/104136 bytes in 192ms 
12-18 11:33:00.396: INFO/WindowManager(577): Config changed: { scale=1.0 imsi=0/0 locale=en_US touch=3 key=2/1/2 nav=3 orien=2 } 
12-18 11:33:00.535: DEBUG/StatusBar(577): updateResources 
12-18 11:33:00.595: DEBUG/AndroidRuntime(1763): Shutting down VM 
12-18 11:33:00.595: WARN/dalvikvm(1763): threadid=3: thread exiting with uncaught exception (group=0x4000fe70) 
12-18 11:33:00.605: ERROR/AndroidRuntime(1763): Uncaught handler: thread main exiting due to uncaught exception 
12-18 11:33:00.615: INFO/WindowManager(577): onOrientationChanged, rotation changed to 0 
12-18 11:33:00.625: ERROR/AndroidRuntime(1763): java.lang.RuntimeException: Unable to start activity ComponentInfo{se.bergsland.manydatepickers/se.bergsland.manydatepickers.ManyDatePickers}: java.lang.NullPointerException 
12-18 11:33:00.625: ERROR/AndroidRuntime(1763):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2268) 
12-18 11:33:00.625: ERROR/AndroidRuntime(1763):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2284) 
12-18 11:33:00.625: ERROR/AndroidRuntime(1763):  at android.app.ActivityThread.handleRelaunchActivity(ActivityThread.java:3278) 
12-18 11:33:00.625: ERROR/AndroidRuntime(1763):  at android.app.ActivityThread.access$1900(ActivityThread.java:112) 
12-18 11:33:00.625: ERROR/AndroidRuntime(1763):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1696) 
12-18 11:33:00.625: ERROR/AndroidRuntime(1763):  at android.os.Handler.dispatchMessage(Handler.java:99) 
12-18 11:33:00.625: ERROR/AndroidRuntime(1763):  at android.os.Looper.loop(Looper.java:123) 
12-18 11:33:00.625: ERROR/AndroidRuntime(1763):  at android.app.ActivityThread.main(ActivityThread.java:3948) 
12-18 11:33:00.625: ERROR/AndroidRuntime(1763):  at java.lang.reflect.Method.invokeNative(Native Method) 
12-18 11:33:00.625: ERROR/AndroidRuntime(1763):  at java.lang.reflect.Method.invoke(Method.java:521) 
12-18 11:33:00.625: ERROR/AndroidRuntime(1763):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:782) 
12-18 11:33:00.625: ERROR/AndroidRuntime(1763):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:540) 
12-18 11:33:00.625: ERROR/AndroidRuntime(1763):  at dalvik.system.NativeStart.main(Native Method) 
12-18 11:33:00.625: ERROR/AndroidRuntime(1763): Caused by: java.lang.NullPointerException 
12-18 11:33:00.625: ERROR/AndroidRuntime(1763):  at se.bergsland.manydatepickers.ManyDatePickers.onCreateDialog(ManyDatePickers.java:102) 
12-18 11:33:00.625: ERROR/AndroidRuntime(1763):  at android.app.Activity.restoreManagedDialogs(Activity.java:857) 
12-18 11:33:00.625: ERROR/AndroidRuntime(1763):  at android.app.Activity.performRestoreInstanceState(Activity.java:801) 
12-18 11:33:00.625: ERROR/AndroidRuntime(1763):  at android.app.Instrumentation.callActivityOnRestoreInstanceState(Instrumentation.java:1172) 
12-18 11:33:00.625: ERROR/AndroidRuntime(1763):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2245) 
12-18 11:33:00.625: ERROR/AndroidRuntime(1763):  ... 12 more 

Answer 1

使用此代碼在您的活動：

@Override 

public void onConfigurationChanged(Configuration newConfig) { 
    super.onConfigurationChanged(newConfig); 
} 

使用此清單檔案中的：

<activity android:name="MyActivity" android:label="@string/app_name" 
    android:configChanges="orientation|keyboardHidden"></activity> 

Answer 2

Fargath'我的建議並不是我所害怕的最好的。你的問題是在配置更改後調用onCreateDialog()時activateDate爲空。由於您只在onClick()中設置過一次。您需要將其設置爲onStart()。將它設置爲onResume()將不起作用，但您可能需要將其設置在此處，請參閱我的問題Android lifecycle: Fill in data in activity in onStart() or onResume()?。

如果要在顯示對話框的同時更新日期，則可以通過在onPrepareDialog()中直接執行Calendar.getInstance()。

Fargath的解決方案存在的問題是您隱藏了軟鍵盤，但問題仍然存在於帶有硬件鍵盤（如G1）的設備上。來電也是如此。我不確定與它有什麼關係。