在运行应用程序第二屏幕时出现致命异常

Question

我正在开发一个 android 应用程序，它是 NewsApp。我做了 2 activity。第一个是 MainActivity，第二个是 HomeActivity。 MainActivity 上有一个注册按钮。如果用户按下按钮，MainActivity 将完成并出现 HomeActivity，但在我的情况下，当用户单击注册按钮时，HomeActivity 不会出现并且模拟器显示“应用程序已停止”。

由于我是新手，所以无法发现问题出在哪里，也不知道如何解决。

提前致谢。

我得到的错误是：

E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.project.newsapp, PID: 8723
java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.EditText.setText(java.lang.CharSequence)' on a null object reference
    at com.project.newsapp.HomeActivity.onResponse(HomeActivity.kt:108)
    at retrofit2.ExecutorCallAdapterFactory$ExecutorCallbackCall.run(ExecutorCallAdapterFactory.java:70)
    at android.os.Handler.handleCallback(Handler.java:789)
    at android.os.Handler.dispatchMessage(Handler.java:98)
    at android.os.Looper.loop(Looper.java:164)
    at android.app.ActivityThread.main(ActivityThread.java:6541)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:767)

我还附上了我的 HomeActivity 和 MainActivity 代码，这样你就可以告诉我哪里做错了。

我的家庭活动代码：

package com.project.newsapp

import android.app.ProgressDialog
import android.content.Context
import android.content.Intent
import android.content.SharedPreferences
import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.view.View
import com.project.newsapp.contract.Request
import com.project.newsapp.contract.Response
import com.project.newsapp.network.IRequestContract
import com.project.newsapp.network.NetworkClient
import com.project.newsapp.utils.Constant
import com.project.newsapp.utils.DataProvider
import com.project.newsapp.utils.showToast
import kotlinx.android.synthetic.main.activity_home.*
import kotlinx.android.synthetic.main.activity_home.btnExit
import kotlinx.android.synthetic.main.activity_main.*
import retrofit2.Call
import retrofit2.Callback

class HomeActivity : AppCompatActivity(), Callback<Response>, View.OnClickListener {

lateinit var userId:String
lateinit var userName:String
private val retrofitClient = NetworkClient.getNetworkClient()
private val requestContract = retrofitClient.create(IRequestContract::class.java)
private lateinit var sharedPreferences: SharedPreferences
private lateinit var progressDialog: ProgressDialog

override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_home)

    progressDialog = ProgressDialog(this)
    progressDialog.setMessage("Please wait...")
    progressDialog.setCancelable(true)

    sharedPreferences = getSharedPreferences(Constant.PREF_NAME, Context.MODE_PRIVATE)

    title = "NewsApp"
    userId = intent.getStringExtra(Constant.KEY_USER_ID).toString()
    userName = intent.getStringExtra(Constant.KEY_USER_NAME).toString()

    txtUserName.text = "Welcome $userName"

    btnAllNews.setOnClickListener (this)

    btnMyNews.setOnClickListener (this)

    btnSignOut.setOnClickListener (this)

    btnExit.setOnClickListener (this)

}

override fun onStart() {
    super.onStart()
    progressDialog.show()
    val request = Request(
        action = Constant.GET_NEWS,
        userId = userId
    )
    val callResponse = requestContract.makeApiCall(request)
    callResponse.enqueue(this)
}

override fun onClick(v: View?) {
    when(v?.id){
        R.id.btnAllNews -> {
            if(DataProvider.response.allNews.size>0){
                Intent(this,ViewAllNewsActivity::class.java).apply {
                    startActivity(this)
                }
            }else{
                showToast("Blogs are not available")
            }
        }
        R.id.btnMyNews -> {

        }
        R.id.btnSignOut -> {
            signOut()
        }
    }
}
private fun signOut(){
    val editor = sharedPreferences.edit()
    editor.clear().commit()

    Intent(this,MainActivity::class.java).apply{
        startActivity(this)
        finish()
    }
}

override fun onResponse(call: Call<Response>, response: retrofit2.Response<Response>) {
    if(progressDialog.isShowing)
        progressDialog.dismiss()

    if(response.body()!=null){
        val serverResponse = response.body()
        if(serverResponse!!.status){
            DataProvider.response = serverResponse
        }else{
            showToast(serverResponse.message)
            edUserName.setText("")
        }
    }
    else{
        showToast("Server is not responding. Please try again later.")
    }
}

override fun onFailure(call: Call<Response>, t: Throwable) {
    if(progressDialog.isShowing)
        progressDialog.dismiss()

    showToast("Server is not responding. Please try again later.")
}}

我的 MainActivity 代码：

package com.project.newsapp

import android.app.ProgressDialog
import android.content.Context
import android.content.Intent
import android.content.SharedPreferences
import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import com.project.newsapp.contract.Request
import com.project.newsapp.contract.Response
import com.project.newsapp.network.IRequestContract
import com.project.newsapp.network.NetworkClient
import com.project.newsapp.utils.Constant
import com.project.newsapp.utils.showToast
import kotlinx.android.synthetic.main.activity_main.*
import retrofit2.Call
import retrofit2.Callback

class MainActivity : AppCompatActivity(), Callback<Response> {

private val retrofitClient = NetworkClient.getNetworkClient()
private val requestContract = retrofitClient.create(IRequestContract::class.java)
private lateinit var progressDialog:ProgressDialog
private lateinit var sharedPreferences:SharedPreferences
lateinit var userName:String

override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_main)

    progressDialog = ProgressDialog(this)
    progressDialog.setMessage("Please wait...")
    progressDialog.setCancelable(true)

    sharedPreferences = getSharedPreferences(Constant.PREF_NAME, Context.MODE_PRIVATE)

    checkIfUserAlreadyRegistered()

    btnRegister.setOnClickListener {
        userName = edUserName.text.toString().trim().uppercase()
        if(userName.isNullOrEmpty()){
            showToast("Please Enter your Name")
        }else{
            progressDialog.show()
            val request = Request(
                action = Constant.REGISTER_USER,
                userName = userName
            )
            val callResponse = requestContract.makeApiCall(request)
            callResponse.enqueue(this)
        }
    }

    /*btnExit.setOnClickListener {
        finish()
    }*/
}

override fun onFailure(call: Call<Response>, t: Throwable) {
    if(progressDialog.isShowing)
        progressDialog.dismiss()

    showToast("Server is not responding. Please try again later.")
    edUserName.setText("")
}

override fun onResponse(call: Call<Response>, response: retrofit2.Response<Response>) {
    if(progressDialog.isShowing)
        progressDialog.dismiss()

    if(response.body()!=null){
        val serverResponse = response.body()
        if(serverResponse!!.status){
            saveUserToPref(serverResponse.userId,userName)
            Intent(this, HomeActivity::class.java).apply {
                putExtra(Constant.KEY_USER_ID, serverResponse.userId)
                putExtra(Constant.KEY_USER_NAME, userName)
                startActivity(this)
                finish()
            }
        }else{
            showToast(serverResponse.message)
            edUserName.setText("")
        }
    }
    else{
        showToast("Server is not responding. Please try again later.")
        edUserName.setText("")
    }
}

private fun saveUserToPref(userId:String, userName:String){
    val editor = sharedPreferences.edit()
    editor.putString(Constant.KEY_USER_ID,userId)
    editor.putString(Constant.KEY_USER_NAME,userName)
    editor.commit()
}

private fun checkIfUserAlreadyRegistered(){
    val userId = sharedPreferences.getString(Constant.KEY_USER_ID,"invalid user id")
    val userName = sharedPreferences.getString(Constant.KEY_USER_NAME,"invalid user name")

    if(!userId.contentEquals("invalid user id")
        && !userName.contentEquals("invalid user name")){
        Intent(this, HomeActivity::class.java).apply {
            putExtra(Constant.KEY_USER_ID, userId)
            putExtra(Constant.KEY_USER_NAME, userName)
            startActivity(this)
            finish()
        }
    }
}}

Answer 1

Kotlin 合成访问器已弃用。

它们被弃用的原因之一是它们会导致您看到的错误。 edUserName 似乎是 null，这意味着 R.layout.activity_home 实际上没有 ID 映射到 edUserName 的小部件。

问题可能来自：

import kotlinx.android.synthetic.main.activity_main.*

很可能，那不应该在 HomeActivity 中，因为您没有在那里使用 activity_main。

在 运行 应用程序第二屏幕时出现致命异常

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在运行应用程序第二屏幕时出现致命异常