我尝试从MainActivity更新我的应用中的进度条，但它不允许我引用片段内的任何内容。如果我通过使用它来引用片段，但片段会在所有内容之下呈现（因为我的应用程序会在单个活动中切换片段）。由于进度条的原因，我尝试过的任何内容都会在运行时返回NullPointerException。
My Fragment的.java文件：
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));
}
}
我尝试了各种不同的解决方案，看了一下，几乎到处都看到人们说要给片段充气，但它却被夸大了，我不知道为什么它不是。工作...任何帮助将不胜感激！我还是Java的新手！ ：P我确定我一直是个白痴，我不能看到我做过的......
P.S。我试图从布局中获取的所有内容都存在于XML文件中，所以......不是这样！ ：P
这是我的fragment for fragment_server_status
的XML
<?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>
我按照建议添加OnViewCreated，运行它并且...... :(仍然是一个NullpointerException。玩得开心：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)
答案 0 :(得分：3)
似乎在片段膨胀之前调用refresh。这意味着onCreateView尚未被调用，cpuPercentage仍为空。
如果您确实需要从片段外部调用refresh，请添加检查以查看是否已设置cpuPercentage：
if (myFragment.cpuPercentage != null) {
myFragment.refresh();
}
以同样的方式将检查添加到每个其他字段，即ramPercentage和tempValue。
注意：我认为这些字段不应该是静态的。