Java 传递带有意图的整数将导致空对象引用
我在方法中添加了一个新的意图,即将整数值传递给另一个活动。然而,我在接收端得到一个空对象引用/空指针异常。 这是调用方法(昆虫是一个ID为整数的自定义类型) 这是接收类:Java 传递带有意图的整数将导致空对象引用,java,android,android-studio,Java,Android,Android Studio,我在方法中添加了一个新的意图,即将整数值传递给另一个活动。然而,我在接收端得到一个空对象引用/空指针异常。 这是调用方法(昆虫是一个ID为整数的自定义类型) 这是接收类: package com.ac_companion.wegner; import androidx.appcompat.app.AppCompatActivity; import android.content.Intent; import android.os.Bundle; import android.util.Log
package com.ac_companion.wegner;
import androidx.appcompat.app.AppCompatActivity;
import android.content.Intent;
import android.os.Bundle;
import android.util.Log;
import java.util.ArrayList;
public class InsectDetails extends AppCompatActivity {
private final String TAG = "InsectDetails";
private int insectPositionMarker;
private Insect localInsect;
public int insectId;
//private Intent mIntent = new Intent();
public InsectDetails(){
Intent mIntent = getIntent();
insectId = mIntent.getIntExtra("InsectDetails", 0);
}
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_insect_details);
localInsect = Util.getGlobalInsectList().get(insectId);
}
}
这是一个例外:
E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.ac_companion.wegner, PID: 16344
java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.ac_companion.wegner/com.ac_companion.wegner.InsectDetails}: java.lang.NullPointerException: Attempt to invoke virtual method 'int android.content.Intent.getIntExtra(java.lang.String, int)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2548)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2707)
at android.app.ActivityThread.-wrap12(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1460)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6077)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:866)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:756)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'int android.content.Intent.getIntExtra(java.lang.String, int)' on a null object reference
at com.ac_companion.wegner.InsectDetails.<init>(InsectDetails.java:20)
at java.lang.Class.newInstance(Native Method)
at android.app.Instrumentation.newActivity(Instrumentation.java:1078)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2538)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2707)
at android.app.ActivityThread.-wrap12(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1460)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6077)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:866)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:756)
E/AndroidRuntime:致命异常:主
流程:com.ac_companion.wegner,PID:16344
java.lang.RuntimeException:无法实例化活动组件信息{com.ac_companion.wegner/com.ac_companion.wegner.InsectDetails}:java.lang.NullPointerException:尝试在空对象引用上调用虚拟方法'int android.content.Intent.getIntExtra(java.lang.String,int)'
在android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2548)
位于android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2707)
位于android.app.ActivityThread.-wrap12(ActivityThread.java)
在android.app.ActivityThread$H.handleMessage(ActivityThread.java:1460)上
位于android.os.Handler.dispatchMessage(Handler.java:102)
位于android.os.Looper.loop(Looper.java:154)
位于android.app.ActivityThread.main(ActivityThread.java:6077)
位于java.lang.reflect.Method.invoke(本机方法)
在com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:866)上
位于com.android.internal.os.ZygoteInit.main(ZygoteInit.java:756)
原因:java.lang.NullPointerException:尝试在空对象引用上调用虚拟方法“int android.content.Intent.getIntExtra(java.lang.String,int)”
请访问com.ac_companion.wegner.InsectDetails。(InsectDetails.java:20)
位于java.lang.Class.newInstance(本机方法)
位于android.app.Instrumentation.newActivity(Instrumentation.java:1078)
在android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2538)
位于android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2707)
位于android.app.ActivityThread.-wrap12(ActivityThread.java)
在android.app.ActivityThread$H.handleMessage(ActivityThread.java:1460)上
位于android.os.Handler.dispatchMessage(Handler.java:102)
位于android.os.Looper.loop(Looper.java:154)
位于android.app.ActivityThread.main(ActivityThread.java:6077)
位于java.lang.reflect.Method.invoke(本机方法)
在com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:866)上
位于com.android.internal.os.ZygoteInit.main(ZygoteInit.java:756)
为什么我的
minent.getIntExtra
是空对象?据我所知,它已正确初始化。我认为这是因为活动生命周期。您不应该在活动中使用构造函数。只需在@OnCreate
方法中移动代码即可
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_insect_details);
Intent mIntent = getIntent();
insectId = mIntent.getIntExtra("InsectDetails", 0);
localInsect = Util.getGlobalInsectList().get(insectId);
}
您会得到一个异常,因为您试图在创建活动之前获得意图
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_insect_details);
Intent mIntent = getIntent();
insectId = mIntent.getIntExtra("InsectDetails", 0);
localInsect = Util.getGlobalInsectList().get(insectId);
}