Android手机app启动的时候第一个Activity必须是MainActivity吗

不是必须的。在AndroidManifest.xml文件中，可以通过设置intent-filter来指定启动Activity的方式。如果你指定了某个Activity为launcher Activity，并设置了intent-filter为ACTION_MAIN和CATEGORY_LAUNCHER，那么这个Activity就会成为应用程序的入口点，即启动Activity。如果你希望在应用程序启动时打开的不是MainActivity，可以在AndroidManifest.xml文件中更改launcher Activity的设置。

相关问题

出现以下报错的原因，改怎么解决，修改哪里2023-06-06 22:04:47.620 3151-3151/com.example.notepad E/AndroidRuntime: FATAL EXCEPTION: main Process: com.example.notepad, PID: 3151 java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.notepad/com.example.notepad.MainActivity}: android.view.InflateException: Binary XML file line #32: addView(View, LayoutParams) is not supported in AdapterView at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2954) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3089) at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78) at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108) at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68) at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1819) at android.os.Handler.dispatchMessage(Handler.java:106) at android.os.Looper.loop(Looper.java:193) at android.app.ActivityThread.main(ActivityThread.java:6737) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:860) Caused by: android.view.InflateException: Binary XML file line #32: addView(View, LayoutParams) is not supported in AdapterView Caused by: java.lang.UnsupportedOperationException: addView(View, LayoutParams) is not supported in AdapterView at android.widget.AdapterView.addView(AdapterView.java:503) at android.view.LayoutInflater.rInflate(LayoutInflater.java:867) at android.view.LayoutInflater.rInflateChildren(LayoutInflater.java:824) at android.view.LayoutInflater.rInflate(LayoutInflater.java:866) at android.view.LayoutInflater.rInflateChildren(LayoutInflater.java:824) at android.view.LayoutInflater.inflate(LayoutInflater.java:515) at android.view.LayoutInflater.inflate(LayoutInflater.java:423) at android.view.LayoutInflater.inflate(LayoutInflater.java:374) at com.android.internal.policy.PhoneWindow.setContentView(PhoneWindow.java:420) at android.app.Activity.setContentView(Activity.java:2772) at com.example.notepad.MainActivity.onCreate(MainActivity.java:30) at android.app.Activity.performCreate(Activity.java:7144) at android.app.Activity.performCreate(Activity.java:7135) at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1271) at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2934) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3089) at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78) at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108) at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68) at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1819) at android.os.Handler.dispatchMessage(Handler.java:106) at android.os.Looper.loop(Looper.java:193) at android.app.ActivityThread.main(ActivityThread.java:6737) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:860)

这个报错的原因是在一个 AdapterView 中使用了 addView() 方法，而这个方法是不支持在 AdapterView 中使用的。根据报错信息，您的问题可能出现在您的 MainActivity 的第 30 行。请检查该行代码所在的布局文件，确保其中没有在 AdapterView 中使用 addView() 方法。如果有，请将其删除或替换为适当的方法。

另外，也请确保您的应用程序中的所有布局文件都正确地使用了布局约束和布局规则。如果您还没有使用这些约束和规则，请查阅 Android 官方文档以了解更多信息。

java.lang.RuntimeException: Failure delivering result ResultInfo{who=null, request=2, result=-1, data=Intent { act=inline-data (has extras) }} to activity {com.example.camerax_final/com.example.camerax_final.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String android.net.Uri.toString()' on a null object reference at android.app.ActivityThread.deliverResults(ActivityThread.java:4845) at android.app.ActivityThread.handleSendResult(ActivityThread.java:4886) at android.app.servertransaction.ActivityResultItem.execute(ActivityResultItem.java:51) at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135) at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95) at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2016) at android.os.Handler.dispatchMessage(Handler.java:107) at android.os.Looper.loop(Looper.java:214) at android.app.ActivityThread.main(ActivityThread.java:7356) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:930) Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String android.net.Uri.toString()' on a null object reference at com.example.camerax_final.MainActivity.onActivityResult(MainActivity.java:87) at android.app.Activity.dispatchActivityResult(Activity.java:8110) at android.app.ActivityThread.deliverResults(ActivityThread.java:4838) at android.app.ActivityThread.handleSendResult(ActivityThread.java:4886) at android.app.servertransaction.ActivityResultItem.execute(ActivityResultItem.java:51) at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135) at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95) at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2016) at android.os.Handler.dispatchMessage(Handler.java:107) at android.os.Looper.loop(Looper.java:214) at android.app.ActivityThread.main(ActivityThread.java:7356) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:930)

这个错误信息是由于在 onActivityResult() 方法中，尝试调用一个 null 对象的方法导致的 NullPointerException。具体来说，是在该方法的第 87 行尝试调用了一个 null 对象的 toString() 方法，而这个对象是一个 Uri 对象。因此，你需要先检查 onActivityResult() 方法中获取的 Intent 是否包含有效的 Uri 数据，如果 Uri 为 null，则需要避免调用 toString() 方法。