findViewById（）从片段内返回null-Android

Question

I'm trying to update progress bars in my app from MainActivity, however it does not let me reference anything that's inside the fragments. If I reference the fragment by using It works but the fragment renders underneath everything (As my app switches fragments out inside a single activity). Anything I've tried returns a NullPointerException on runtime due to the progress bars.

My Fragment's .java file:

 package com.example.adam.slypanel; import android.app.Fragment; import android.os.Bundle; import android.support.annotation.Nullable; import android.view.LayoutInflater; import android.view.View; import android.view.ViewGroup; import android.widget.ProgressBar; import java.util.Random; /** * Created by root on 02/10/14. */ public class ServerStatusFragment extends Fragment{ public static ProgressBar cpuPercentage; public static ProgressBar ramPercentage; public static ProgressBar tempValue; public ServerStatusFragment() { } @Nullable @Override public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) { View ServerStatusView = inflater.inflate(R.layout.fragment_server_status, container, false); //Right here! D: cpuPercentage = (ProgressBar) ServerStatusView.findViewById(R.id.cpuUsageBar); ramPercentage = (ProgressBar) ServerStatusView.findViewById(R.id.ramUsageBar); tempValue = (ProgressBar) ServerStatusView.findViewById(R.id.tempBar); return (ServerStatusView); } //For testing -- Replace when needed public static int randInt(int min, int max) { // NOTE: Usually this should be a field rather than a method // variable so that it is not re-seeded every call. Random rand = new Random(); // nextInt is normally exclusive of the top value, // so add 1 to make it inclusive int randomNum = rand.nextInt((max - min) + 1) + min; return randomNum; } public void refresh() { cpuPercentage.setProgress(randInt(0, 100)); ramPercentage.setProgress(randInt(0, 100)); tempValue.setProgress(randInt(20, 100)); } } 

I've tried various different solutions, Looked around for a bit and pretty much everywhere I've seen people saying to inflate the fragment, yet it is inflated and I have no idea why it isn't working... Any help will be much appreciated! I'm still a newbie to Java! :P I'm sure I've been an idiot with it and i just can't see what I've done...

Ps Everything I'm trying to get from the layout is present in the XML file so... It's not that! :P

Here's my XML for fragment_server_status

 <?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:orientation="vertical" android:layout_width="match_parent" android:layout_height="match_parent" android:id="@+id/Server_Status_Fragment" android:weightSum="1"> <RelativeLayout android:layout_width="match_parent" android:layout_height="match_parent"> <TextView android:layout_width="wrap_content" android:layout_height="wrap_content" android:textAppearance="?android:attr/textAppearanceLarge" android:text="CPU Usage: " android:id="@+id/cpuUsageLabel" android:layout_alignParentTop="true" android:layout_alignParentLeft="true" android:layout_alignParentStart="true" android:layout_marginTop="30dp" android:layout_marginLeft="20dp" /> <TextView android:layout_width="wrap_content" android:layout_height="wrap_content" android:textAppearance="?android:attr/textAppearanceLarge" android:text="RAM Usage: " android:id="@+id/ramUsageLabel" android:layout_toEndOf="@+id/tempLabel" android:layout_below="@+id/cpuUsageBar" android:layout_alignLeft="@+id/cpuUsageBar" android:layout_alignStart="@+id/cpuUsageBar" android:layout_marginTop="45dp" /> <TextView android:layout_width="wrap_content" android:layout_height="wrap_content" android:textAppearance="?android:attr/textAppearanceLarge" android:text="Temperature" android:id="@+id/tempLabel" android:layout_below="@+id/ramUsageBar" android:layout_alignRight="@+id/cpuUsageLabel" android:layout_alignEnd="@+id/cpuUsageLabel" android:layout_marginTop="52dp" /> <ProgressBar style="?android:attr/progressBarStyleHorizontal" android:layout_width="wrap_content" android:layout_height="25dp" android:id="@+id/cpuUsageBar" android:max="100" android:progress="25" android:indeterminate="false" android:layout_marginTop="40dp" android:layout_below="@+id/cpuUsageLabel" android:layout_alignLeft="@+id/cpuUsageLabel" android:layout_alignStart="@+id/cpuUsageLabel" /> <ProgressBar style="?android:attr/progressBarStyleHorizontal" android:layout_width="120dp" android:layout_height="25dp" android:id="@+id/ramUsageBar" android:max="100" android:progress="45" android:indeterminate="false" android:layout_toEndOf="@+id/tempBar" android:layout_centerVertical="true" android:layout_alignLeft="@+id/ramUsageLabel" android:layout_alignStart="@+id/ramUsageLabel" /> <ProgressBar style="?android:attr/progressBarStyleHorizontal" android:layout_width="120dp" android:layout_height="25dp" android:id="@+id/tempBar" android:max="100" android:progress="60" android:indeterminate="false" android:layout_marginTop="65dp" android:layout_below="@+id/tempLabel" android:layout_alignLeft="@+id/tempLabel" android:layout_alignStart="@+id/tempLabel" /> </RelativeLayout> </LinearLayout> 

I added in OnViewCreated as suggested, ran it and... :( Still a NullpointerException. Have fun with the log :D

 01-09 16:26:39.571 7746-7746/com.example.adam.slypanel E/AndroidRuntime﹕ FATAL EXCEPTION: main Process: com.example.adam.slypanel, PID: 7746 java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.adam.slypanel/com.example.adam.slypanel.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ProgressBar.setProgress(int)' on a null object reference at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2298) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360) at android.app.ActivityThread.access$800(ActivityThread.java:144) at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278) at android.os.Handler.dispatchMessage(Handler.java:102) at android.os.Looper.loop(Looper.java:135) at android.app.ActivityThread.main(ActivityThread.java:5221) 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:898) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:693) Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ProgressBar.setProgress(int)' on a null object reference at com.example.adam.slypanel.ServerStatusFragment.refresh(ServerStatusFragment.java:55) at com.example.adam.slypanel.MainActivity$1.run(MainActivity.java:77) at com.example.adam.slypanel.MainActivity.onSectionAttached(MainActivity.java:107) at com.example.adam.slypanel.MainActivity$PlaceholderFragment.onAttach(MainActivity.java:234) at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:853) at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:1067) at android.app.BackStackRecord.run(BackStackRecord.java:833) at android.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1452) at android.app.Activity.performStart(Activity.java:5948) at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2261)            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)            at android.app.ActivityThread.access$800(ActivityThread.java:144)            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)            at android.os.Handler.dispatchMessage(Handler.java:102)            at android.os.Looper.loop(Looper.java:135)            at android.app.ActivityThread.main(ActivityThread.java:5221)            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:898)            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:693) 

Answer 1

It seems that you call refresh before the fragment is inflated. That means onCreateView wasn't yet called and cpuPercentage is still null.

If you really need to call refresh from outside of your fragment, then add checks to see if cpuPercentage is set yet:

if (myFragment.cpuPercentage != null) {
    myFragment.refresh();
}

In the same way add checks to every other field too, ie ramPercentage and tempValue.

Note: it looks to me that these fields shouldn't be static.