[英]Get value from another class
我想从另一个班级获得价值,但是当我在第二堂课上获得价值时,它为null。 我认为这是由于bcs何时向此String添加了某些内容而导致代码无法运行。
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);
很多不重要的代码.......................................
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.
很多非关键的代码....................................
mMap.setOnMarkerClickListener(new GoogleMap.OnMarkerClickListener() {
@Override
public boolean onMarkerClick(final Marker marker) {
很多不重要的代码...........................................
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();
}
这是...。我在计时器完成后将值设置为receiveEmail,但是我必须通过单击地图上的标记来运行计时器。 我无法在此计时器bcs值之外设置值receiveEmail。 因此,当我在另一个类中调用它时,通常:
MapsActivity mapsActivity = new MapsActivity();
recipientUsername2 = mapsActivity.getRecipientEmail();
Log.i("values2", mapsActivity.recipientEmail);
在运行第二项活动后,应用崩溃。
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)
请问你能帮帮我吗?
在这里,您将创建一个新的 MapsActivity
实例(可能为空 ):
MapsActivity mapsActivity = new MapsActivity();
在下面的两行中,您尝试阅读以下内容:
recipientUsername2 = mapsActivity.getRecipientEmail();
难怪它是空的。 这个MapsActivity不是您要寻找的MapsActivity ... (这只是绝地绝招)。
尽量把握这样说:当您设置recipientEmail
在MapsActivity场,你把它写在一张纸上。 随着new MapsActivity()
构造函数调用,你得到的文件从你的抽屉里一个新的作品-一个不同的,而现在你试着读的东西掉纸张,您对其他一书中写道...
为了获得该信息,您必须将其放置在某处-将其设置为您要传递的类的实例,将其设置为您计划在下一个使用的类中的字段,等等。
然而,这一次,我想设置recipientEmail
字符串作为额外的SendMail
活动将是要走的路:
Intent intent = new Intent(getApplicationContext(), SendMessage.class);
intent.putExtra("RECIPIENT_EMAIL", marker.getTitle());
startActivity(intent); //this has to be after the putExtra call
当您尝试在SendMail
活动中访问它时:
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,请阅读当我不得不处理Extras时通常会转向的这个问题的答案。
另一件事:访问对象成员的推荐方法是将其设置为私有vland add getter方法,并在适用时设置setter方法。 仅使变量可访问是有问题的。
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