這是我在 Navigation Drawer Activity 中的 mainActivity .kt 檔案。當我使用 onclicklistener 時，它會使我的應用程式崩潰，但當我在 oncreate 函式之外使用 onClick 時，它會正常運行。使用 Onclicklistener 我的構建沒有給出任何錯誤，但 logcat 中有一些錯誤。
package com.example.android.chatapplication
import android.content.Intent
import android.os.Bundle
import android.view.Menu
import android.view.View
import android.widget.Button
import android.widget.ImageButton
import com.google.android.material.snackbar.Snackbar
import com.google.android.material.navigation.NavigationView
import androidx.navigation.findNavController
import androidx.navigation.ui.AppBarConfiguration
import androidx.navigation.ui.navigateUp
import androidx.navigation.ui.setupActionBarWithNavController
import androidx.navigation.ui.setupWithNavController
import androidx.drawerlayout.widget.DrawerLayout
import androidx.appcompat.app.AppCompatActivity
import com.example.android.chatapplication.databinding.ActivityMainBinding
class MainActivity : AppCompatActivity() {
private lateinit var appBarConfiguration: AppBarConfiguration
private lateinit var binding: ActivityMainBinding
val loginbtn : Button = findViewById(R.id.loginButtonNavHeader)
val addchannelbtn : ImageButton = findViewById(R.id.addChannelButton)
val sendmessagebtn : ImageButton = findViewById(R.id.sendMessageBtn)
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
binding = ActivityMainBinding.inflate(layoutInflater)
setContentView(binding.root)
setSupportActionBar(binding.appBarMain.toolbar)
// when I write the below onclicklisener my app crashes . but simply works properly when a use onClick .
loginbtn.setOnClickListener {
val loginIntent = Intent(this, LoginActivity::class.java)
startActivity(loginIntent)
}
val drawerLayout: DrawerLayout = binding.drawerLayout
val navView: NavigationView = binding.navView
val navController = findNavController(R.id.nav_host_fragment_content_main)
appBarConfiguration = AppBarConfiguration(
setOf(
R.id.nav_home, R.id.nav_gallery, R.id.nav_slideshow
), drawerLayout
)
setupActionBarWithNavController(navController, appBarConfiguration)}
Logcat 錯誤
Process: com.example.android.chatapplication, PID: 6449
java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.android.chatapplication/com.example.android.chatapplication.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.pm.ApplicationInfo android.content.Context.getApplicationInfo()' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3637)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3896)
at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:85)
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:140)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:100)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2326)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loop(Looper.java:263)
at android.app.ActivityThread.main(ActivityThread.java:8296)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:612)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1006)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.pm.ApplicationInfo android.content.Context.getApplicationInfo()' on a null object reference
at android.content.ContextWrapper.getApplicationInfo(ContextWrapper.java:183)
at android.view.ContextThemeWrapper.getTheme(ContextThemeWrapper.java:174)
at android.content.Context.obtainStyledAttributes(Context.java:744)
at androidx.appcompat.app.AppCompatDelegateImpl.createSubDecor(AppCompatDelegateImpl.java:852)
at androidx.appcompat.app.AppCompatDelegateImpl.ensureSubDecor(AppCompatDelegateImpl.java:819)
at androidx.appcompat.app.AppCompatDelegateImpl.findViewById(AppCompatDelegateImpl.java:640)
at androidx.appcompat.app.AppCompatActivity.findViewById(AppCompatActivity.java:261)
at com.example.android.chatapplication.MainActivity.<init>(MainActivity.kt:25)
at java.lang.Class.newInstance(Native Method)
at android.app.AppComponentFactory.instantiateActivity(AppComponentFactory.java:95)
at androidx.core.app.CoreComponentFactory.instantiateActivity(CoreComponentFactory.java:45)
at android.app.Instrumentation.newActivity(Instrumentation.java:1254)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3625)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3896)
at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:85)
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:140)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:100)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2326)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loop(Looper.java:263)
at android.app.ActivityThread.main(ActivityThread.java:8296)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:612)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1006)
當使用下面的代碼時，我的應用程式運行得很好。
fun loginbtnclicked(view : View ){
val loginIntent = Intent(this, LoginActivity::class.java)
startActivity(loginIntent)
}
uj5u.com熱心網友回復：
您findViewById()在活動生命周期中呼叫得太早。移動這些：
val loginbtn : Button = findViewById(R.id.loginButtonNavHeader)
val addchannelbtn : ImageButton = findViewById(R.id.addChannelButton)
val sendmessagebtn : ImageButton = findViewById(R.id.sendMessageBtn)
通話后onCreate()。setContentView()
轉載請註明出處，本文鏈接：https://www.uj5u.com/net/511616.html