【创建了一个View，对其使用setVisibility（）方法，运行时报空指针】

创建了一个View，对其使用setVisibility（）方法，运行时报空指针

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详细描述

截图

2018-11-10 20:41:32.250 25639-25639/? E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.forrestsu.logintest, PID: 25639
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.forrestsu.logintest/com.example.forrestsu.logintest.activity.MapModeActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.view.View.setVisibility(int)' on a null object reference
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2822)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2897)
        at android.app.ActivityThread.-wrap11(Unknown Source:0)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1598)
        at android.os.Handler.dispatchMessage(Handler.java:105)
        at android.os.Looper.loop(Looper.java:251)
        at android.app.ActivityThread.main(ActivityThread.java:6572)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:767)
     Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.view.View.setVisibility(int)' on a null object reference
        at com.example.forrestsu.logintest.activity.MapModeActivity.initView(MapModeActivity.java:96)
        at com.example.forrestsu.logintest.activity.MapModeActivity.onCreate(MapModeActivity.java:86)
        at android.app.Activity.performCreate(Activity.java:6975)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1214)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2775)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2897) 
        at android.app.ActivityThread.-wrap11(Unknown Source:0) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1598) 
        at android.os.Handler.dispatchMessage(Handler.java:105) 
        at android.os.Looper.loop(Looper.java:251) 
        at android.app.ActivityThread.main(ActivityThread.java:6572) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:767) 
2018-11-10 20:41:32.251 25639-25639/? D/MtaSDK: [main(2): null:61] - MTA has caught the following uncaught exception:
2018-11-10 20:41:32.251 25639-25639/? E/MtaSDK: java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.forrestsu.logintest/com.example.forrestsu.logintest.activity.MapModeActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.view.View.setVisibility(int)' on a null object reference
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2822)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2897)
        at android.app.ActivityThread.-wrap11(Unknown Source:0)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1598)
        at android.os.Handler.dispatchMessage(Handler.java:105)
        at android.os.Looper.loop(Looper.java:251)
        at android.app.ActivityThread.main(ActivityThread.java:6572)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:767)
     Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.view.View.setVisibility(int)' on a null object reference
        at com.example.forrestsu.logintest.activity.MapModeActivity.initView(MapModeActivity.java:96)
        at com.example.forrestsu.logintest.activity.MapModeActivity.onCreate(MapModeActivity.java:86)
        at android.app.Activity.performCreate(Activity.java:6975)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1214)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2775)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2897) 
        at android.app.ActivityThread.-wrap11(Unknown Source:0) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1598) 
        at android.os.Handler.dispatchMessage(Handler.java:105) 
        at android.os.Looper.loop(Looper.java:251) 
        at android.app.ActivityThread.main(ActivityThread.java:6572) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:767)

代码

布局文件
<View
        android:id="@+id/glass_view"
        android:layout_width="0dp"
        android:layout_height="0dp"
        android:background="@color/transparent"
        android:clickable="true"
        android:focusable="true"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/view_top" />

代码
private View glassView；

......

glassView = (View) findViewById(R.id.view_glass);
glassView.setVisibility(GONE);
        glassView.setOnClickListener(new MyOnClickListener());

编辑于2024-04-23

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[北京|结业弟子]Android-苏正荣
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控件id写错了，布局中是glass_view,代码中引用的是view_glass
findViewById（）报空指针错误一般有以下几种情况
1.布局文件有问题；
2.在设置contentView之前findViewById（）；
3.以前使用Eclipse开发时需要clean项目。

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编辑于2018-11-17

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