Hey there, let's get to the bottom of why your app crashes right after the splash screen—this is a super common issue, so we'll break it down step by step to fix it!

The crash log will tell you exactly what's going wrong, so don't skip this:

• Open the Logcat window in Android Studio (look for it in the bottom toolbar)
• Filter logs by Error level, or just search for AndroidRuntime
• Look for the entry with FATAL EXCEPTION—it'll include the crash type (like NullPointerException, ClassNotFoundException) and even the exact line of code causing the problem

For example, if you see NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference, that means you're trying to use a Button that wasn't properly initialized.

A lot of crashes happen during the transition between screens. Here's what to verify:

• Did you properly register your LoginActivity in AndroidManifest.xml? You should have a <activity> tag for it, otherwise the system can't find it when you try to launch it.
• Is your startActivity call correct? It should look like this:

  startActivity(new Intent(SplashActivity.this, LoginActivity.class));
  

  Make sure you're using a valid Context (don't use a Context that's already been destroyed, like if you're using a Handler delay, double-check the Context reference).
• Are there theme conflicts? If your splash screen uses a fullscreen theme, make sure the login activity's theme is compatible—mismatched themes can cause unexpected crashes.

You mentioned using simple Java code on the login screen—let's check the usual culprits:

• Did you initialize your views? If you're calling setOnClickListener or getText() on a Button/EditText without first doing findViewById(R.id.your_view_id), you'll get a null pointer crash. Always initialize views after calling setContentView(R.layout.activity_login).
• Is setContentView correctly set? Double-check that you're inflating the right layout file for the login activity—if you use the wrong layout ID or the layout is missing, the app will crash when trying to load the screen.
• Are you doing network operations on the main thread? If your login code makes a network call (like sending credentials to a server) directly in the main thread, Android will throw a NetworkOnMainThreadException. Move network code to a background thread using AsyncTask, Coroutines, or a library like Retrofit.
• Are any variables uninitialized? If you declare a variable (like EditText usernameEt;) but never assign it a value before using it, that's a guaranteed crash.

• Permissions: If your login screen uses network access, make sure you've added <uses-permission android:name="android.permission.INTERNET"/> in AndroidManifest.xml.
• Dependency Compatibility: If you're using third-party libraries (like for login SDKs), make sure their versions are compatible with your app's target SDK version.
• Android Version Compatibility: If you're using APIs introduced in newer Android versions (like Android 13's notification permissions), add checks to handle older devices gracefully.

Suppose your Logcat points to a null pointer on line 25 of LoginActivity.java where you set a click listener on a login button. Here's how to fix it:

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_login); // Critical: Load the layout first
    
    // Initialize the button before using it
    Button loginBtn = findViewById(R.id.login_button);
    loginBtn.setOnClickListener(v -> {
        // Your login logic here
    });
}

Once you have the crash log, you can narrow down the issue even faster—feel free to share the log snippet if you still need help!

内容的提问来源于stack exchange，提问作者Shubham Goyal