Button visibility don´t change

Question

In my Android Studio I try to change the visibility of a Button when I click another Button.

public void doSelect(View view2) {
    Button unterschrifftButton = (Button) findViewById(R.id.unterschriftButton);
    unterschrifftButton.setVisibility(View.VISIBLE);
}

When I click this button the app crashes. I dont know what i have to do now. Logcat says:

2021-01-20 09:17:08.723 11938-11938/com.example.parseapp E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.parseapp, PID: 11938
java.lang.IllegalStateException: Could not execute method for android:onClick
    at androidx.appcompat.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:402)
    at android.view.View.performClick(View.java:5610)
    at android.view.View$PerformClick.run(View.java:22265)
    at android.os.Handler.handleCallback(Handler.java:751)
    at android.os.Handler.dispatchMessage(Handler.java:95)
    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$MethodAndArgsCaller.run(ZygoteInit.java:866)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:756)
 Caused by: java.lang.reflect.InvocationTargetException
    at java.lang.reflect.Method.invoke(Native Method)
    at androidx.appcompat.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:397)
    at android.view.View.performClick(View.java:5610) 
    at android.view.View$PerformClick.run(View.java:22265) 
    at android.os.Handler.handleCallback(Handler.java:751) 
    at android.os.Handler.dispatchMessage(Handler.java:95) 
    at android.os.Looper.loop(Looper.java:154) 
    at android.app.ActivityThread.main(ActivityThread.java:6077) 
    at java.lang.reflect.Method.invoke(Native Method) 
    at com.android.internal.os.ZygoteInit$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 'void android.view.View.setVisibility(int)' on a null object reference
    at com.example.parseapp.MainActivity.doSelect(MainActivity.java:243)
    at java.lang.reflect.Method.invoke(Native Method) 
    at androidx.appcompat.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:397) 
    at android.view.View.performClick(View.java:5610) 
    at android.view.View$PerformClick.run(View.java:22265) 
    at android.os.Handler.handleCallback(Handler.java:751) 
    at android.os.Handler.dispatchMessage(Handler.java:95) 
    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)

Does this answer your question? [Unfortunately MyApp has stopped. How can I solve this?](https://stackoverflow.com/questions/23353173/unfortunately-myapp-has-stopped-how-can-i-solve-this) — a_local_nobody, Jan 19 '21 at 08:54
See [What is a NullPointerException, and how do I fix it?](https://stackoverflow.com/q/218384/208273) — Ryan M, Jan 20 '21 at 09:22

score 1 · Answer 1 · edited Jan 19 '21 at 11:43

Try this, your casting was wrong!

private Button action;

@Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_video_reverse);

        action = findViewById(R.id.unterschrifftButton);

        action.setOnClickListener(v -> {
            unterschrifftButton.setVisibility(View.VISIBLE);
        });

    }

Button visibility don´t change

1 Answers1