Android中的倒數計時器錯誤

Question

我搜索了它，但任何解決方案無法解決我的問題。 我在一個片段中實現了一個計時器，但是我的應用程序停止工作顯示一個錯誤。

這是我的應用程序的工作。 當用戶點擊開始按鈕時，它會將用戶帶到下一個活動，其中片段顯示在容器（RelativeLayout）中。我在片段中實現了Count CountDownTimer函數。在CountDownTimer函數之前，片段完美工作。

任何幫助？ 這是代碼。

Start.java

package com.example.sheikhspc.timerexample; 

import android.app.Fragment; 
import android.app.FragmentManager; 
import android.app.FragmentTransaction; 
import android.support.v7.app.AppCompatActivity; 
import android.os.Bundle; 

public class Start extends AppCompatActivity { 

Fragment frag = null; 
@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_start); 
    FragmentManager fm = getFragmentManager(); 
    FragmentTransaction fragmentTransaction = fm.beginTransaction(); 

    frag = new BlankFragment1(); 
    fragmentTransaction.replace(R.id.container,frag); 

    fragmentTransaction.commit(); 





    } 
} 

MainActivity.java

package com.example.sheikhspc.timerexample; 

import android.content.Intent; 
import android.support.v7.app.AppCompatActivity; 
import android.os.Bundle; 
import android.view.View; 
import android.widget.Button; 

public class MainActivity extends AppCompatActivity { 

Button btn; 
@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_main); 
    btn = (Button)findViewById(R.id.startbtn); 
} 

public void start(View view) 
{ 
    Intent intent = new Intent(this,Start.class); 
    startActivity(intent); 
} 
} 

BlankFragment1.java

package com.example.sheikhspc.timerexample; 


import android.os.Bundle; 
import android.app.Fragment; 
import android.os.CountDownTimer; 
import android.provider.DocumentsContract; 
import android.view.LayoutInflater; 
import android.view.View; 
import android.view.ViewGroup; 
import android.widget.TextView; 
import android.widget.Toast; 


public class BlankFragment1 extends Fragment { 


public BlankFragment1() { 
    // Required empty public constructor 
} 


Fragment frag = null; 
TextView tv; 
View root; 
@Override 
public View onCreateView(LayoutInflater inflater, ViewGroup container, 
         Bundle savedInstanceState) { 
    // Inflate the layout for this fragment 
    tv = (TextView)root.findViewById(R.id.timer1); 

    new CountDownTimer(30000, 1000) { 

     public void onTick(long millisUntilFinished) { 
      tv.setText("seconds remaining: " + millisUntilFinished/1000); 
      //here you can have your logic to set text to edittext 
     } 

     public void onFinish() { 
      tv.setText("done!"); 
     } 

    }.start(); 



    return inflater.inflate(R.layout.fragment_blank_fragment1, container, false); 
} 

} 

錯誤日誌

 E/AndroidRuntime: FATAL EXCEPTION: main 
    Process: com.example.sheikhspc.timerexample, PID: 28970 
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.sheikhspc.timerexample/com.example.sheikhspc.timerexamp le.Start}: 
    java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.view.View.findViewById(int)' on a null object reference 

    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2339) 
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2413) 
        at android.app.ActivityThread.access$800(ActivityThread.java:155) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1317) 
        at android.os.Handler.dispatchMessage(Handler.java:102) 
        at android.os.Looper.loop(Looper.java:135) 
        at android.app.ActivityThread.main(ActivityThread.java:5343) 
        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:905) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:700) 
       Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.view.View.findViewById(int)' on a null object reference 
        at com.example.sheikhspc.timerexample.BlankFragment1.onCreateView(BlankFragment1.java:46) 
        at android.app.Fragment.performCreateView(Fragment.java:2053) 
        at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:894) 
        at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:1067) 
        at android.app.BackStackRecord.run(BackStackRecord.java:834) 
        at android.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1454) 
        at android.app.Activity.performStart(Activity.java:6025) 
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2302) 
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2413)  
        at android.app.ActivityThread.access$800(ActivityThread.java:155)  
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1317)  
        at android.os.Handler.dispatchMessage(Handler.java:102)  
        at android.os.Looper.loop(Looper.java:135)  
        at android.app.ActivityThread.main(ActivityThread.java:5343)  
        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:905)  
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:700)  
Application terminated. 

Answer 1

在OnCreateView

View v = inflater.inflate(R.layout.fragment_blank_fragment1, null); 

，然後通過v.findViewById找到的物品，並返回充氣View

return v; 

或者您也可以通過

root = inflater.inflate(R.layout.fragment_blank_fragment1, null); 

tv = (TextView) root.findViewById(...); 
// other implementations 

return root;