Java Android正在从枚举获取结果
我正在尝试获取我在此处传递的枚举的值:Java Android正在从枚举获取结果,java,android,nullpointerexception,Java,Android,Nullpointerexception,我正在尝试获取我在此处传递的枚举的值: Intent intent = new Intent(MainActivity.this, SelectBrush.class); Bundle bundle = new Bundle(); bundle.putString("Current brush", myFingerPainter.getBrush().name());
Intent intent = new Intent(MainActivity.this, SelectBrush.class);
Bundle bundle = new Bundle();
bundle.putString("Current brush", myFingerPainter.getBrush().name());
intent.putExtras(bundle);
startActivityForResult(intent, BRUSH_REQUEST_CODE );
我试着在第二个活动中把它说出来:
Paint.Cap brushStyle = Paint.Cap.valueOf(getIntent().getStringExtra("Current brush"));
这是我的日志:
Process: com.example.myapplication, PID: 26592
java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.myapplication/com.example.myapplication.SelectBrush}: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String android.content.Intent.getStringExtra(java.lang.String)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2567)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2726)
at android.app.ActivityThread.-wrap12(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1477)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6119)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String android.content.Intent.getStringExtra(java.lang.String)' on a null object reference
at com.example.myapplication.SelectBrush.<init>(SelectBrush.java:17)
at java.lang.Class.newInstance(Native Method)
at android.app.Instrumentation.newActivity(Instrumentation.java:1078)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2557)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2726)
at android.app.ActivityThread.-wrap12(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1477)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6119)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)
但我也有一个类似的例外:
2020-10-31 11:55:38.921 28148-28148/com.example.myapplication E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.myapplication, PID: 28148
java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.myapplication/com.example.myapplication.SelectBrush}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.os.Bundle android.content.Intent.getExtras()' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2567)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2726)
at android.app.ActivityThread.-wrap12(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1477)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6119)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.os.Bundle android.content.Intent.getExtras()' on a null object reference
at com.example.myapplication.SelectBrush.<init>(SelectBrush.java:16)
at java.lang.Class.newInstance(Native Method)
at android.app.Instrumentation.newActivity(Instrumentation.java:1078)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2557)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2726)
at android.app.ActivityThread.-wrap12(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1477)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6119)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)
2020-10-31 11:55:38.921 28148-28148/com.example.myapplication E/AndroidRuntime:FATAL EXCEPTION:main
进程:com.example.myapplication,PID:28148
java.lang.RuntimeException:无法实例化activity ComponentInfo{com.example.myapplication/com.example.myapplication.SelectBrush}:java.lang.NullPointerException:尝试在空对象引用上调用虚拟方法“android.os.Bundle android.content.Intent.getExtras()”
在android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2567)
位于android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2726)
位于android.app.ActivityThread.-wrap12(ActivityThread.java)
在android.app.ActivityThread$H.handleMessage(ActivityThread.java:1477)上
位于android.os.Handler.dispatchMessage(Handler.java:102)
位于android.os.Looper.loop(Looper.java:154)
位于android.app.ActivityThread.main(ActivityThread.java:6119)
位于java.lang.reflect.Method.invoke(本机方法)
在com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)上
位于com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)
原因:java.lang.NullPointerException:尝试对空对象引用调用虚拟方法“android.os.Bundle android.content.Intent.getExtras()”
在com.example.myapplication.SelectBrush.(SelectBrush.java:16)
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:2557)上
位于android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2726)
位于android.app.ActivityThread.-wrap12(ActivityThread.java)
在android.app.ActivityThread$H.handleMessage(ActivityThread.java:1477)上
位于android.os.Handler.dispatchMessage(Handler.java:102)
位于android.os.Looper.loop(Looper.java:154)
位于android.app.ActivityThread.main(ActivityThread.java:6119)
位于java.lang.reflect.Method.invoke(本机方法)
在com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)上
位于com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)
我读过很多书,我认为这是因为第二个活动认为intent==null,但我不确定为什么,因为我在第一个类中创建了它。只需在onCreate方法中添加以下行:
String brushString = bundle.getString("Current brush");
brushStyle = Paint.Cap.valueOf(brushString);
在班级层面:
Paint.Cap brushStyle;
您的活动意图(
getIntent()
)是null
,这很奇怪。您确定这是在onCreate()中或之后调用的吗?当它为null
时,似乎只有两种情况:尝试在此Paint.Cap brushStyle=Paint.Cap.valueOf(brushString)处设置断点代码>您将了解错误是出于意图还是在为brushStyle
Paint.Cap brushStyle;