Java NullPointerException:是否尝试对空对象引用调用虚拟方法?
在尝试调用按钮上的方法时,我收到NUllPointerException:Java NullPointerException:是否尝试对空对象引用调用虚拟方法?,java,android,nullpointerexception,Java,Android,Nullpointerexception,在尝试调用按钮上的方法时,我收到NUllPointerException: private FButton fButton1; ... ... fButton1 = (FButton) findViewById(R.id.FButton1); fButton1.setButtonColor(ContextCompat.getColor(this, fbutton_color_turquoise)); //Exception here 我正在使用,但我不明白为什么会出现异常 错误日志: F
private FButton fButton1;
...
...
fButton1 = (FButton) findViewById(R.id.FButton1);
fButton1.setButtonColor(ContextCompat.getColor(this, fbutton_color_turquoise)); //Exception here
我正在使用,但我不明白为什么会出现异常
错误日志:
FATAL EXCEPTION: main
Process: com.user.app, PID: 11209
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.user.app/com.user.app.activities.StartUpScreen}: java.lang.NullPointerException: Attempt to invoke virtual method 'void info.hoang8f.widget.FButton.setButtonColor(int)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2416)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)
at android.app.ActivityThread.-wrap11(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void info.hoang8f.widget.FButton.setButtonColor(int)' on a null object reference
at com.user.app.activities.StartUpScreen.onCreate(StartUpScreen.java:44)
at android.app.Activity.performCreate(Activity.java:6237)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1107)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2369)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)
at android.app.ActivityThread.-wrap11(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
my layout.xml,其中FButton是:
<info.hoang8f.widget.FButton
fbutton:buttonColor="@color/fbutton_color_turquoise"
fbutton:shadowColor="@color/fbutton_color_green_sea"
fbutton:shadowEnabled="true"
fbutton:shadowHeight="5dp"
android:text="Celcius"
android:textColor="#FFF"
fbutton:cornerRadius="5dp"
android:layout_marginTop="8dp"
app:layout_constraintTop_toBottomOf="@+id/imageButton3"
android:layout_marginLeft="8dp"
app:layout_constraintLeft_toLeftOf="parent"
android:layout_height="wrap_content"
android:layout_marginStart="8dp"
android:layout_width="match_parent"
android:id="@+id/FButton1"
app:layout_constraintRight_toLeftOf="@+id/FButton2"
android:layout_marginRight="8dp"
android:layout_marginEnd="8dp"
app:layout_constraintHorizontal_bias="1.0" />
我必须创建的ids.xml文件,因为android没有重新编码id:
<?xml version="1.0" encoding="utf-8"?>
<resources>
<item name="FButton1" type="id" />
</resources>
您的
fButton1
似乎为空。
只需检查调用findViewById的位置并检查xml文件中是否确实存在此元素设置按钮颜色时出错,使用此选项以编程方式更改按钮的颜色
setBackgroundColor(getResources().getColor(R.color.holo_light_green))
还有一件事,从Android支持库开始-23 getColor方法已被弃用,因此请改用此方法
ContextCompat.getColor(context, R.color.your_color);
因此,要支持所有版本,请使用此
public static final int getColor(Context context, int id)
{
final int version = Build.VERSION.SDK_INT;
if (version >= 23) {
return ContextCompatApi23.getColor(context, id);
}
else {
return context.getResources().getColor(id);
}
}
写满callstack@Vyacheslav完成编辑下的检查@这个空点异常没有任何意义,所有其他视图都是以这种方式在我的代码中声明的,它们都工作得很好。这与Android Studio在创建
FButton
时“找不到id”有关吗?我被迫创建一个ids.xml
文件并添加
,这样我的findViewById()
、ids.xml
和layout.xml
中的id都是相同的,但它仍然抛出相同的异常,有什么想法吗?getColor
被贬低,来自同一库的所有其他方法也不起作用。我也有同样的例外。我想它回答了你的问题