When you click on the button, the application crashes and "Unfortunately, OnClick has stoped" .

 TextView tv; @Override protected void onCreate(Bundle savedInstanceState) { tv = (TextView) findViewById(R.id.textView); super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); } public void Click(View view) { tv.setText("HELLO"); } 

 <Button android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="HELLO" android:id="@+id/button" android:layout_alignParentTop="true" android:layout_centerHorizontal="true" android:onClick="Click"/> <TextView android:layout_width="wrap_content" android:layout_height="wrap_content" android:textAppearance="?android:attr/textAppearanceLarge" android:id="@+id/textView" android:layout_centerVertical="true" android:layout_alignEnd="@+id/button" />

This is what logcat produces :

Process: com.example.sadie.onclick, PID: 5068 java.lang.IllegalStateException: Could not execute a method for android: onClick at android.support.v7.app.AppCompatViewInflater $ DeclaredOnClickListener.onClick (AppCompatViewInflater.java dem 93 .view.View.performClick (View.java:4780) at android.view.View $ PerformClick.run (View.java:19866) at android.os.Handler.handleCallback (Handler.java:739) at android.os. Handler.dispatchMessage (Handler.java:95) at android.os.Looper.loop (Looper.java:135) at android.app.ActivityThread.main (ActivityThread.java 12.25) at java.lang.reflect.Method.invoke (Native Method) at java.lang.reflect.Method.invoke (Method.javaUE72) at com.android.internal.os.ZygoteInit $ MethodAndArgsCaller.run (ZygoteInit.java:903) at com.android.internal.os .ZygoteInit.main (ZygoteInit.java:698) Caused by: java.lang.reflect.InvocationTargetException at java.lang.reflect.Method.invoke (Native Method) at java.lang.reflect.Method.invoke (Method.java: 372) at android.support.v7.app.AppCompatView Inflater $ DeclaredOnClickListener.onClick (AppCompatViewInflater.java:288) at android.view.View.performClick (View.java:4780) at android.view.View $ PerformClick.run (View.java:19866) at android.os.Handler .handleCallback (Handler.java:739) at android.os.Handler.dispatchMessage (Handler.java:95) at android.os.Looper.loop (Looper.java:135) at android.app.ActivityThread.main (ActivityThread. java: 5254) at java.lang.reflect.Method.invoke (Native Method) at java.lang.reflect.Method.invoke (Method.java=72) at com.android.internal.os.ZygoteInit $ MethodAndArgsCaller.run ( ZygoteInit.java:903) at com.android.internal.os.ZygoteInit.main (ZygoteInit.java:698) Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText (java .lang.CharSequence) 'on a null object reference at com.example.sadie.onclick.MainActivity.Click (MainActivity.java:20) at java.lang.reflect.Method.invoke (Native Method) at java.lang.reflect .Method.invoke (Method.javaUE72) at android.support.v7 .app.AppCompatViewInflater $ DeclaredOnClickListener.onClick (AppCompatViewInflater.java:288) at android.view.View.performClick (View.java:4780) at android.view.View $ PerformClick.run (View.java:19866) at android. os.Handler.handleCallback (Handler.java:739) at android.os.Handler.dispatchMessage (Handler.java:95) at android.os.Looper.loop (Looper.java:135) at android.app.ActivityThread.main (ActivityThread.java Lower254) at java.lang.reflect.Method.invoke (Native Method) at java.lang.reflect.Method.invoke (Method.java complete72) at com.android.internal.os.ZygoteInit $ MethodAndArgsCaller .run (ZygoteInit.java:903) at com.android.internal.os.ZygoteInit.main (ZygoteInit.java:698) 06-19 01: 34: 01.044 5068-5068 / com.example.sadie.onclick I / Process : Sending signal. PID: 5068 SIG: 9

    1 answer 1

    Apparently the problem is that the links to the widgets in the markup (the result of the method ( findViewById() ) must be obtained after the markup is attached to the activation (the result of the work of the method setContentView() :

     @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); tv = (TextView) findViewById(R.id.textView); }

    Now you are trying to refer to a non-existent widget in the click method, since the result of the search widget without a connected markup will be null and get an action.

    PS: method names in Java are written with a small letter. Callback methods are usually started with on- - onClick() - it is necessary to comply with the convention if you want other developers not to think any nasty things about you :)

    • Thank you very much ! I messed around with this error all day. - sherzod.sadiev