App crashes while changing the orientation from landscape to portrait

问题

ERROR **2020-03-01 17:36:58.959 6589-6589/com.studenthelper.bscit E/AndroidRuntime: FATAL EXCEPTION: main Process: com.studenthelper.bscit, PID: 6589 java.lang.RuntimeException: Unable to start activity ComponentInfo{com.studenthelper.bscit/com.studenthelper.bscit.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2914) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3049) at android.app.ActivityThread.handleRelaunchActivityInner(ActivityThread.java:4785) at android.app.ActivityThread.handleRelaunchActivity(ActivityThread.java:4694) at android.app.servertransaction.ActivityRelaunchItem.execute(ActivityRelaunchItem.java:69) at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108) at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68) at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1809) at android.os.Handler.dispatchMessage(Handler.java:106) at android.os.Looper.loop(Looper.java:193) at android.app.ActivityThread.main(ActivityThread.java:6692) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858) 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.studenthelper.bscit.MainActivity.onCreate(MainActivity.java:21) at android.app.Activity.performCreate(Activity.java:7140) at android.app.Activity.performCreate(Activity.java:7131) at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1272) at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2894) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3049) at android.app.ActivityThread.handleRelaunchActivityInner(ActivityThread.java:4785) at android.app.ActivityThread.handleRelaunchActivity(ActivityThread.java:4694) at android.app.servertransaction.ActivityRelaunchItem.execute(ActivityRelaunchItem.java:69) at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108) at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68) at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1809) at android.os.Handler.dispatchMessage(Handler.java:106) at android.os.Looper.loop(Looper.java:193) at android.app.ActivityThread.main(ActivityThread.java:6692) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858) **

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN,WindowManager.LayoutParams.FLAG_FULLSCREEN);
    TextView textView=findViewById(R.id.logotext);
    int unicode=0x1F4A1;
    String emoji=getEmoji(unicode);
    String Text="Bsc"+emoji+"T";
    textView.setText(Text);

}
public String getEmoji(int uni)
{
    return new String(Character.toChars(uni));
}

回答1:

As per your crash logs:

com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858) 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.studenthelper.bscit.MainActivity.onCreate(MainActivity.java:20)

It means your textView

TextView textView=findViewById(R.id.logotext);

Is not found from the layout R.layout.activity_main due to which when you try to textView.setText(Text); it's actually null and exception occurs.

So, I'll suggest to

Verify textVIew Id is same in the layout? and
Set the getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN,WindowManager.LayoutParams.FLAG_FULLSCREEN); before the setContentView(R.layout.activity_main);

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState); 
    getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN,WindowManager.LayoutParams.FLAG_FULLSCREEN);
    setContentView(R.layout.activity_main);
    TextView textView=findViewById(R.id.logotext);
    int unicode=0x1F4A1;
    String emoji=getEmoji(unicode);
    String Text="Bsc"+emoji+"T";
    textView.setText(Text);

}

来源：https://stackoverflow.com/questions/60458106/app-crashes-while-changing-the-orientation-from-landscape-to-portrait

标签

java

android

android-studio