启动我的应用程序后,它立即崩溃。由于某种原因,它声明了一个IllegalArgumentException,尽管我不明白为什么。我已经正确实例化了setContentView。我试图不带R.id就将参数设置为activity_main,尽管我没有任何位置,而我在stackoverflow上看了一会儿。

错误:

06-14 17:00:44.262 6209-6209/com.example.jarvis_main.chatapptest E/AndroidRuntime: FATAL EXCEPTION: main
                                                                               Process: com.example.jarvis_main.chatapptest, PID: 6209
                                                                               java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.jarvis_main.chatapptest/com.example.jarvis_main.chatapptest.MainActivity}: java.lang.IllegalArgumentException: Cannot add a null child view to a ViewGroup
                                                                                   at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2817)
                                                                                   at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2892)
                                                                                   at android.app.ActivityThread.-wrap11(Unknown Source:0)
                                                                                   at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1593)
                                                                                   at android.os.Handler.dispatchMessage(Handler.java:105)
                                                                                   at android.os.Looper.loop(Looper.java:164)
                                                                                   at android.app.ActivityThread.main(ActivityThread.java:6540)
                                                                                   at java.lang.reflect.Method.invoke(Native Method)
                                                                                   at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240)
                                                                                   at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:767)
                                                                                Caused by: java.lang.IllegalArgumentException: Cannot add a null child view to a ViewGroup
                                                                                   at android.view.ViewGroup.addView(ViewGroup.java:4647)
                                                                                   at android.view.ViewGroup.addView(ViewGroup.java:4629)
                                                                                   at android.support.v7.app.AppCompatDelegateImplV9.setContentView(AppCompatDelegateImplV9.java:283)
                                                                                   at android.support.v7.app.AppCompatActivity.setContentView(AppCompatActivity.java:145)
                                                                                   at com.example.jarvis_main.chatapptest.MainActivity.onCreate(MainActivity.java:40)
                                                                                   at android.app.Activity.performCreate(Activity.java:6980)
                                                                                   at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1213)
                                                                                   at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2770)
                                                                                   at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2892) 
                                                                                   at android.app.ActivityThread.-wrap11(Unknown Source:0) 
                                                                                   at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1593) 
                                                                                   at android.os.Handler.dispatchMessage(Handler.java:105) 
                                                                                   at android.os.Looper.loop(Looper.java:164) 
                                                                                   at android.app.ActivityThread.main(ActivityThread.java:6540) 
                                                                                   at java.lang.reflect.Method.invoke(Native Method) 
                                                                                   at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240) 
                                                                                   at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:767) 

码:
package com.example.jarvis_main.chatapptest;

import android.content.Intent;
import android.text.format.DateFormat;
import android.support.annotation.NonNull;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.Snackbar;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.EditText;
import android.widget.ListView;
import android.widget.RelativeLayout;
import android.widget.TextView;


import com.firebase.ui.auth.AuthUI;
import com.firebase.ui.database.FirebaseListAdapter;
import com.google.android.gms.tasks.OnCompleteListener;
import com.google.android.gms.tasks.Task;
import com.google.firebase.auth.FirebaseAuth;
import com.google.firebase.database.FirebaseDatabase;

import static com.example.jarvis_main.chatapptest.R.layout.activity_main;

public class MainActivity extends AppCompatActivity {

private static int SignInRequestCode = 1;
private FirebaseListAdapter<ChatMessage> adapter;
RelativeLayout activity_main;
FloatingActionButton fab;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    activity_main = (RelativeLayout)findViewById(R.id.activity_main);

    setContentView(R.layout.activity_main);
    fab = (FloatingActionButton)findViewById(R.id.fab);
    fab.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            EditText input = (EditText)findViewById(R.id.input);
            FirebaseDatabase.getInstance().getReference().push().setValue(new ChatMessage(input.getText().toString(), FirebaseAuth.getInstance().getCurrentUser().getEmail()));
            input.setText("");
        }
    });

    if(FirebaseAuth.getInstance().getCurrentUser() == null)
    {
        startActivityForResult(AuthUI.getInstance().createSignInIntentBuilder().build(),SignInRequestCode);
    }
    else
    {
        Snackbar.make(activity_main, "Welcome "+FirebaseAuth.getInstance().getCurrentUser().getEmail(), Snackbar.LENGTH_SHORT).show();
        //Load content
        displayChatMessage();
    }
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    if(item.getItemId() == R.id.menu_sign_out){
        AuthUI.getInstance().signOut(this).addOnCompleteListener(new OnCompleteListener<Void>(){
           @Override
                   public void onComplete(@NonNull Task<Void> Task){
                    Snackbar.make(activity_main,"Successfully signed out. Bye!", Snackbar.LENGTH_SHORT).show();
                    finish();
            }
        });
    }
    return true;
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    getMenuInflater().inflate(R.menu.main_menu,menu);

    return true;
}

@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
    super.onActivityResult(requestCode, resultCode, data);
    if(requestCode == SignInRequestCode)
    {
        if(resultCode == RESULT_OK)
        {
            Snackbar.make(activity_main,"Successfully signed in. Welcome!", Snackbar.LENGTH_SHORT).show();
            displayChatMessage();
        }
        else{
            Snackbar.make(activity_main,"We couldn't sign you in.Please try again later", Snackbar.LENGTH_SHORT).show();
            finish();
        }
    }
}

private void displayChatMessage(){
    ListView listOfMsg = (ListView)findViewById(R.id.list_of_message);
    adapter = new FirebaseListAdapter<ChatMessage>(this, ChatMessage.class,R.layout.list_item,FirebaseDatabase.getInstance().getReference()) {
        @Override
        protected void populateView(View v, ChatMessage model, int position) {
            TextView messageText,messageUser,messageTime;
            messageText = (TextView) findViewById(R.id.message_text);
            messageUser = (TextView) findViewById(R.id.message_user);
            messageTime = (TextView) findViewById(R.id.message_time);

            messageText.setText(model.getMessageTexts());
            messageUser.setText(model.getMessageUsers());
            messageTime.setText(DateFormat.format("dd-MM-yyyy (HH:mm:ss)", model.getMessageTime()));

        }
    };
    listOfMsg.setAdapter(adapter);
}


}

最佳答案

在尝试获取子视图的句柄之前,请确保设置内容视图。

像这样:

. . .
setContentView(R.layout.activity_main);
activity_main = (RelativeLayout)findViewById(R.id.activity_main);
.
.

07-23 21:40