这里有一些 Android 代码给我一个空对象引用错误。不知道为什么会这样，但是我发现这与 setStep() 方法有关。不确定是什么导致了这个错误，但这是我在 logcat 中得到的:
02-26 23:00:14.081 24821-24821/com.android.usagemonitor E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: com.android.usagemonitor, PID: 24821
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.android.usagemonitor/com.android.usemoncore.Activities.TypeActivities.NetActivity}: android.view.InflateException: Binary XML file line #7: Binary XML file line #7: Error inflating class com.android.usemoncore.Views.TypeLinearLayouts.NetLinearLayout
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3254)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3350)
at android.app.ActivityThread.access$1100(ActivityThread.java:222)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1795)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:158)
at android.app.ActivityThread.main(ActivityThread.java:7229)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120)
Caused by: android.view.InflateException: Binary XML file line #7: Binary XML file line #7: Error inflating class com.android.usemoncore.Views.TypeLinearLayouts.NetLinearLayout
at android.view.LayoutInflater.inflate(LayoutInflater.java:551)
at android.view.LayoutInflater.inflate(LayoutInflater.java:429)
at android.view.LayoutInflater.inflate(LayoutInflater.java:380)
at com.android.internal.policy.PhoneWindow.setContentView(PhoneWindow.java:474)
at android.app.Activity.setContentView(Activity.java:2387)
at com.android.usemoncore.Activities.TypeActivities.NetActivity.onCreate(NetActivity.java:12)
at android.app.Activity.performCreate(Activity.java:6876)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1135)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3207)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3350)
at android.app.ActivityThread.access$1100(ActivityThread.java:222)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1795)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:158)
at android.app.ActivityThread.main(ActivityThread.java:7229)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230)at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120)
Caused by: android.view.InflateException: Binary XML file line #7: Error inflating class com.android.usemoncore.Views.TypeLinearLayouts.NetLinearLayout
at android.view.LayoutInflater.createView(LayoutInflater.java:657)
at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:776)
at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:716)
at android.view.LayoutInflater.rInflate(LayoutInflater.java:847)
at android.view.LayoutInflater.rInflateChildren(LayoutInflater.java:810)
at android.view.LayoutInflater.rInflate(LayoutInflater.java:855)
at android.view.LayoutInflater.rInflateChildren(LayoutInflater.java:810)
at android.view.LayoutInflater.inflate(LayoutInflater.java:527)
at android.view.LayoutInflater.inflate(LayoutInflater.java:429)
at android.view.LayoutInflater.inflate(LayoutInflater.java:380)
at com.android.internal.policy.PhoneWindow.setContentView(PhoneWindow.java:474)
at android.app.Activity.setContentView(Activity.java:2387)
at com.android.usemoncore.Activities.TypeActivities.NetActivity.onCreate(NetActivity.java:12)
at android.app.Activity.performCreate(Activity.java:6876)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1135)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3207)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3350)
at android.app.ActivityThread.access$1100(ActivityThread.java:222)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1795)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:158)
at android.app.ActivityThread.main(ActivityThread.java:7229)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120)
Caused by: java.lang.reflect.InvocationTargetException
at java.lang.reflect.Constructor.newInstance(Native Method)
at android.view.LayoutInflater.createView(LayoutInflater.java:631)
at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:776)
at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:716)
at android.view.LayoutInflater.rInflate(LayoutInflater.java:847)
at android.view.LayoutInflater.rInflateChildren(LayoutInflater.java:810)
at android.view.LayoutInflater.rInflate(LayoutInflater.java:855)
at android.view.LayoutInflater.rInflateChildren(LayoutInflater.java:810)
at android.view.LayoutInflater.inflate(LayoutInflater.java:527)
at android.view.LayoutInflater.inflate(LayoutInflater.java:429)
at android.view.LayoutInflater.inflate(LayoutInflater.java:380)
at com.android.internal.policy.PhoneWindow.setContentView(PhoneWindow.java:474)
at android.app.Activity.setContentView(Activity.java:2387)
at com.android.usemoncore.Activities.TypeActivities.NetActivity.onCreate(NetActivity.java:12)
at android.app.Activity.performCreate(Activity.java:6876)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1135)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3207)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3350)
at android.app.ActivityThread.access$1100(ActivityThread.java:222)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1795)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:158)
at android.app.ActivityThread.main(ActivityThread.java:7229)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void com.android.usemoncore.Views.GraphView.setStep(float)' on a null object reference
at com.android.usemoncore.Views.TypeLinearLayouts.NetLinearLayout.<init>(NetLinearLayout.java:22)
at java.lang.reflect.Constructor.newInstance(Native Method)
at android.view.LayoutInflater.createView(LayoutInflater.java:631)
at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:776)
at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:716)
at android.view.LayoutInflater.rInflate(LayoutInflater.java:847)
at android.view.LayoutInflater.rInflateChildren(LayoutInflater.java:810)
at android.view.LayoutInflater.rInflate(LayoutInflater.java:855)
at android.view.LayoutInflater.rInflateChildren(LayoutInflater.java:810)
at android.view.LayoutInflater.inflate(LayoutInflater.java:527)
at android.view.LayoutInflater.inflate(LayoutInflater.java:429)
at android.view.LayoutInflater.inflate(LayoutInflater.java:380)
at com.android.internal.policy.PhoneWindow.setContentView(PhoneWindow.java:474)
at android.app.Activity.setContentView(Activity.java:2387)
at com.android.usemoncore.Activities.TypeActivities.NetActivity.onCreate(NetActivity.java:12)
at android.app.Activity.performCreate(Activity.java:6876)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1135)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3207)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3350)
at android.app.ActivityThread.access$1100(ActivityThread.java:222)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1795)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:158)
at android.app.ActivityThread.main(ActivityThread.java:7229)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120)
这是有问题的 NetLinearLayout.java 代码:
import android.content.Context;
import android.util.AttributeSet;
import android.util.Log;
import com.android.usemon.R;
import com.android.usemoncore.Views.GraphView;
import com.android.usemoncore.Views.GraphsLinearLayout;
public class NetLinearLayout extends GraphsLinearLayout {
private GraphView downview;
private GraphView upview;
public NetLinearLayout(Context context, AttributeSet attrs) {
super(context, attrs);
downview = (GraphView) findViewById(R.id.downgraph);
upview = (GraphView) findViewById(R.id.upgraph);
inflate(context, R.layout.linear_net, this);
Log.i("NetLinearLayout", "UpView Val:" + upview);
Log.i("NetLinearLayout", "DownView Val:" + downview);
this.upview.setStep(this.step);
this.downview.setStep(this.step);
}
protected void Scale(float multiplier) {
this.upview.Scale(multiplier);
this.downview.Scale(multiplier);
}
public void setStep(float step) {
this.upview.setStep(step);
this.downview.setStep(step);
}
public void noVLines() {
this.upview.setNovlines(true);
this.downview.setNovlines(true);
this.upview.setTopvertical(false);
}
public void setToShow(int x, int y) {
this.upview.setToShow(x, y);
this.downview.setToShow(x, y);
}
}
这是 Linear_net.xml 的代码:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout android:orientation="vertical" android:layout_width="fill_parent" android:layout_height="fill_parent"
xmlns:android="http://schemas.android.com/apk/res/android" xmlns:custom="http://schemas.android.com/apk/res-auto">
<com.android.usemoncore.Views.GraphView android:id="@+id/upgraph" android:layout_width="fill_parent" android:layout_height="60.0dip" android:layout_weight="1.0" custom:hlines_to_show="2" custom:vlines_to_show="2" custom:fixed_step="3" custom:vertical_top="true" custom:graphdatatype="netup" />
<com.android.usemoncore.Views.GraphView android:id="@+id/downgraph" android:layout_width="fill_parent" android:layout_height="60.0dip" android:layout_weight="1.0" custom:x_reversed="true" custom:hlines_to_show="2" custom:vlines_to_show="2" custom:fixed_step="3" custom:graphdatatype="netdown" />
这是发生错误的代码行:
this.upview.setStep(this.step);
上面代码中的两个地方都发生了此错误。造成这种情况的原因有哪些？任何帮助将不胜感激。
最佳答案
我认为问题是 XML 和代码之间存在某种不匹配。我期望其中一行或两行:
downview = (GraphView) findViewById(R.id.downgraph);
upview = (GraphView) findViewById(R.id.upgraph);
返回 null 而不是 View 。您可以添加调试来确认这一点。我认为原因是这些调用时布局没有膨胀。也许您只需要先进行 inflate 调用即可。
我所说的不匹配是指代码只希望获取 ID，但实际上并没有获取到 ID，因此上下文存在问题。看这个SO question从某种意义上说，这个问题过去曾发生过。但我最近遇到的一个问题是试图找到一个位于与 setContentView() 加载的文件不同的文件中的 id。 This SO question帮我找到了。
关于java - Android - 空对象引用错误，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/42498857/