以最终意图启动 Activity 时应用程序崩溃答案

【问题标题】：app crashes when starting an activity with final intent以最终意图启动 Activity 时应用程序崩溃
【发布时间】：2021-01-12 15:39:12
【问题描述】：

我正在编写一个记录电话的应用程序，此时我正在编写一个菜单，我希望当你点击菜单中的一个对象时，你会转到另一个活动；我试图在这两个活动上都这样做，但是当我点击一个菜单项时，应用程序崩溃了。你能帮我解决这个崩溃吗？我把崩溃的代码和logcat留给你

我的代码：

 //menu
        final Intent go = new Intent(this, records.class);


        bottomNavigationView.setOnNavigationItemSelectedListener(new BottomNavigationView.OnNavigationItemSelectedListener() {
            @Override
            public boolean onNavigationItemSelected(@NonNull MenuItem item) {
                switch (item.getItemId()) {
                    case R.id.action_start:
                        Toast.makeText(MainActivity.this, "Start", Toast.LENGTH_SHORT).show();
                        break;
                    case R.id.action_records:
                        Toast.makeText(MainActivity.this, "Records", Toast.LENGTH_SHORT).show();
                        startRec();
                        break;
                }
                return true;
            }

            private void startRec() {
                startActivity(go);
            }
        });

        //menu code end

崩溃日志：

2021-01-12 16:30:09.637 5101-5101/com.example.ngoctri.introsliderexam E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.ngoctri.introsliderexam, PID: 5101
    java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.ngoctri.introsliderexam/com.conta.app.spyear.records}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.Window$Callback android.view.Window.getCallback()' on a null object reference
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3365)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3601)
        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:85)
        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135)
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2066)
        at android.os.Handler.dispatchMessage(Handler.java:106)
        at android.os.Looper.loop(Looper.java:223)
        at android.app.ActivityThread.main(ActivityThread.java:7656)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:592)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:947)
     Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.Window$Callback android.view.Window.getCallback()' on a null object reference
        at android.support.v7.app.AppCompatDelegateImplBase.<init>(AppCompatDelegateImplBase.java:117)
        at android.support.v7.app.AppCompatDelegateImplV9.<init>(AppCompatDelegateImplV9.java:149)
        at android.support.v7.app.AppCompatDelegateImplV11.<init>(AppCompatDelegateImplV11.java:29)
        at android.support.v7.app.AppCompatDelegateImplV14.<init>(AppCompatDelegateImplV14.java:54)
        at android.support.v7.app.AppCompatDelegateImplV23.<init>(AppCompatDelegateImplV23.java:31)
        at android.support.v7.app.AppCompatDelegateImplN.<init>(AppCompatDelegateImplN.java:31)
        at android.support.v7.app.AppCompatDelegate.create(AppCompatDelegate.java:198)
        at android.support.v7.app.AppCompatDelegate.create(AppCompatDelegate.java:183)
        at android.support.v7.app.AppCompatActivity.getDelegate(AppCompatActivity.java:519)
        at android.support.v7.app.AppCompatActivity.findViewById(AppCompatActivity.java:190)
        at com.conta.app.spyear.records.<init>(records.java:13)
        at java.lang.Class.newInstance(Native Method)
        at android.app.AppComponentFactory.instantiateActivity(AppComponentFactory.java:95)
        at android.app.Instrumentation.newActivity(Instrumentation.java:1253)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3353)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3601) 
        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:85) 
        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135) 
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2066) 
        at android.os.Handler.dispatchMessage(Handler.java:106) 
        at android.os.Looper.loop(Looper.java:223) 
        at android.app.ActivityThread.main(ActivityThread.java:7656) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:592) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:947)

【问题讨论】：

标签： java android crash logcat

【解决方案1】：

at android.support.v7.app.AppCompatActivity.findViewById(AppCompatActivity.java:190)
at com.conta.app.spyear.records.<init>(records.java:13)

问题在于您在第 13 行的 records 活动。您在实例初始化时调用 findViewById() 太早了。将findViewById() 移动到onCreate() 或更高版本，在setContentView() 之后。

【讨论】：