java.lang.RuntimeException：無法啓動活動ComponentInfo Android清單

Question

我收到一個奇怪的錯誤，我不確定它從哪裏來，android清單似乎沒有任何問題，我可以看到。我還添加了主要活動。

錯誤日誌

11-27 09:53:12.364 2553-2553/? E/AndroidRuntime: FATAL EXCEPTION: main 
               Process: com.example.capstoneproject.capstoneproject, PID: 2553 
               java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.capstoneproject.capstoneproject/com.example.capstoneproject.capstoneproject.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.widget.Button.findViewById(int)' on a null object reference 
                at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2325) 
                at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2390) 
                at android.app.ActivityThread.access$800(ActivityThread.java:151) 
                at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1303) 

Android清單

<application 
     android:allowBackup="true" 
     android:icon="@mipmap/ic_launcher" 
     android:label="@string/app_name" 
     android:supportsRtl="true" 
     android:theme="@style/AppTheme"> 
     <activity 
      android:name=".MainActivity" 
      android:label="@string/app_name" 
      android:theme="@style/AppTheme.NoActionBar"> 
      <intent-filter> 
       <action android:name="android.intent.action.MAIN" /> 

       <category android:name="android.intent.category.LAUNCHER" /> 
      </intent-filter> 
     </activity> 
    </application> 

</manifest> 

Mainactivity

package com.example.capstoneproject.capstoneproject; 

import android.os.Bundle; 
import android.support.design.widget.FloatingActionButton; 
import android.support.design.widget.Snackbar; 
import android.support.v7.app.AppCompatActivity; 
import android.support.v7.widget.Toolbar; 
import android.view.View; 
import android.view.Menu; 
import android.view.MenuItem; 
import android.widget.Button; 
import android.widget.TextView; 


public class MainActivity extends AppCompatActivity { 
    Button ConnectButton; 
    TextView StatusText; 


    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.activity_main); 
     Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar); 
     setSupportActionBar(toolbar); 

     ConnectButton.findViewById(R.id.button); 
     StatusText.findViewById(R.id.textView2); 

     FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab); 
     fab.setOnClickListener(new View.OnClickListener() { 
      @Override 
      public void onClick(View view) { 
       Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG) 
         .setAction("Action", null).show(); 


      } 
     }); 
    } 

    public void CButton (View view){ 

     StatusText.setText("Connected"); 
    } 

    @Override 
    public boolean onCreateOptionsMenu(Menu menu) { 
     // Inflate the menu; this adds items to the action bar if it is present. 
     getMenuInflater().inflate(R.menu.menu_main, menu); 
     return true; 
    } 

    @Override 
    public boolean onOptionsItemSelected(MenuItem item) { 
     // Handle action bar item clicks here. The action bar will 
     // automatically handle clicks on the Home/Up button, so long 
     // as you specify a parent activity in AndroidManifest.xml. 
     int id = item.getItemId(); 

     //noinspection SimplifiableIfStatement 
     if (id == R.id.action_settings) { 
      return true; 
     } 

     return super.onOptionsItemSelected(item); 
    } 
} 

Answer 1

變化

ConnectButton.findViewById(R.id.button); 
StatusText.findViewById(R.id.textView2); 

到

ConnectButton = (Button) findViewById(R.id.button); 
StatusText = (TextView) findViewById(R.id.textView2);