[英]Get value from another class
我想從另一個班級獲得價值,但是當我在第二堂課上獲得價值時,它為null。 我認為這是由於bcs何時向此String添加了某些內容而導致代碼無法運行。
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_maps);
// Obtain the SupportMapFragment and get notified when the map is ready to be used.
SupportMapFragment mapFragment = (SupportMapFragment) getSupportFragmentManager()
.findFragmentById(R.id.map);
mapFragment.getMapAsync(this);
很多不重要的代碼.......................................
FirebaseDatabase database5 = FirebaseDatabase.getInstance();
DatabaseReference myRef5 = database5.getReference("userdata");
myRef5.addValueEventListener(new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
// This method is called once with the initial value and again
// whenever data at this location is updated.
很多非關鍵的代碼....................................
mMap.setOnMarkerClickListener(new GoogleMap.OnMarkerClickListener() {
@Override
public boolean onMarkerClick(final Marker marker) {
很多不重要的代碼...........................................
new CountDownTimer(2000, 1000) {
public void onTick(long millisUntilFinished) {
}
public void onFinish() {
progressBar.setVisibility(View.GONE);
textViewPleaseWait.setVisibility(View.INVISIBLE);
recipientEmail = marker.getTitle();
Log.i("omg", recipientEmail);
dialogBuilder.setMessage("Username: " + usernameAlert + "\n" + "Gender: " + genderAlert
+ "\n" + "Age: " + ageAlert + "\n" + marker.getSnippet() + "\n" + marker.getTitle());
dialogBuilder.setPositiveButton("Send message", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface arg0, int arg1) {
Intent intent = new Intent(getApplicationContext(), SendMessage.class);
startActivity(intent);
recipientEmail = marker.getTitle();
}
});
dialogBuilder.setNegativeButton("Close", null);
dialogBuilder.show();
}
}.start();
}
這是...。我在計時器完成后將值設置為receiveEmail,但是我必須通過單擊地圖上的標記來運行計時器。 我無法在此計時器bcs值之外設置值receiveEmail。 因此,當我在另一個類中調用它時,通常:
MapsActivity mapsActivity = new MapsActivity();
recipientUsername2 = mapsActivity.getRecipientEmail();
Log.i("values2", mapsActivity.recipientEmail);
在運行第二項活動后,應用崩潰。
08-28 21:34:25.943 4609-4609/com.samo.facedatefb E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.samo.facedatefb, PID: 4609
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.samo.facedatefb/com.samo.facedatefb.SendMessage}: java.lang.NullPointerException: println needs a message
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2464)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2526)
at android.app.ActivityThread.access$800(ActivityThread.java:169)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1421)
at android.os.Handler.dispatchMessage(Handler.java:111)
at android.os.Looper.loop(Looper.java:194)
at android.app.ActivityThread.main(ActivityThread.java:5549)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:964)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:759)
Caused by: java.lang.NullPointerException: println needs a message
at android.util.Log.println_native(Native Method)
at android.util.Log.i(Log.java:160)
at com.samo.facedatefb.SendMessage.onCreate(SendMessage.java:79)
at android.app.Activity.performCreate(Activity.java:5975)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1111)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2417)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2526)
at android.app.ActivityThread.access$800(ActivityThread.java:169)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1421)
at android.os.Handler.dispatchMessage(Handler.java:111)
at android.os.Looper.loop(Looper.java:194)
at android.app.ActivityThread.main(ActivityThread.java:5549)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:964)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:759)
請問你能幫幫我嗎?
在這里,您將創建一個新的 MapsActivity
實例(可能為空 ):
MapsActivity mapsActivity = new MapsActivity();
在下面的兩行中,您嘗試閱讀以下內容:
recipientUsername2 = mapsActivity.getRecipientEmail();
難怪它是空的。 這個MapsActivity不是您要尋找的MapsActivity ... (這只是絕地絕招)。
盡量把握這樣說:當您設置recipientEmail
在MapsActivity場,你把它寫在一張紙上。 隨着new MapsActivity()
構造函數調用,你得到的文件從你的抽屜里一個新的作品-一個不同的,而現在你試着讀的東西掉紙張,您對其他一書中寫道...
為了獲得該信息,您必須將其放置在某處-將其設置為您要傳遞的類的實例,將其設置為您計划在下一個使用的類中的字段,等等。
然而,這一次,我想設置recipientEmail
字符串作為額外的SendMail
活動將是要走的路:
Intent intent = new Intent(getApplicationContext(), SendMessage.class);
intent.putExtra("RECIPIENT_EMAIL", marker.getTitle());
startActivity(intent); //this has to be after the putExtra call
當您嘗試在SendMail
活動中訪問它時:
String recipientEmail = null;
Bundle extras = getIntent().getExtras();
if(extras == null) {
throw new IllegalStateException("No email address found at SendMail activity!");
} else {
recipientEmail = extras.getString("RECIPIENT_EMAIL");
}
另外,請閱讀當我不得不處理Extras時通常會轉向的這個問題的答案。
另一件事:訪問對象成員的推薦方法是將其設置為私有vland add getter方法,並在適用時設置setter方法。 僅使變量可訪問是有問題的。
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