は、アンドロイドのシンボルsetOnClickListenerを解決できません

Question

私はこのプログラムを実行すると、 "シンボルsetOnClickListenerを解決できません"というメッセージが繰り返し表示されます。

import android.support.v7.app.AppCompatActivity; 

import android.content.Intent; 
import android.os.Bundle; 
import android.support.v7.app.AppCompatActivity; 
import android.view.View; 
import android.view.View.OnClickListener; 
import android.widget.TextView; 

public class MainActivity extends AppCompatActivity { 

@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 

    // Set the content of the activity to use the activity_main.xml layout file 
    setContentView(R.layout.activity_main); 
} 
// Find the View that shows the numbers category 
TextView numbers = (TextView) findViewById(R.id.numbers); 

// Set a click listener on that View 
numbers.setOnClickListener(new View.OnClickListener() { 
    // The code in this method will be executed when the numbers View is clicked on. 
    @Override 
    public void onClick(View view) { 
     Intent numbersIntent = new Intent(MainActivity.this, Numbers.class); 
     startActivity(numbersIntent); 
    } 
} 

}

Answer 1

あなたのコードは、試すonCreateメソッド内でなければなりません：Activity Lifecycle

Answer 2

あなたonClickListenerは、あなたのonCreateメソッドにする必要があります。

public class MainActivity extends AppCompatActivity { 

    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     // Set the content of the activity to use the activity_main.xml layout file 
     setContentView(R.layout.activity_main); 
     // Find the View that shows the numbers category 
     TextView numbers = (TextView) findViewById(R.id.numbers); 

     // Set a click listener on that View 
     numbers.setOnClickListener(new View.OnClickListener() { 
     // The code in this method will be executed when the numbers View is clicked on. 
      @Override 
      public void onClick(View view) { 
       Intent numbersIntent = new Intent(MainActivity.this, Numbers.class); 
       startActivity(numbersIntent); 
      } 
    }); 
    } 
} 

エラーを修正する必要があります。 AndroidManifestにNumbers.classが追加されていることを確認します。そうしないと、インテントを開始するときに別のエラーが発生します。

<activity 
     android:name=".Numbers" 
     android:label="Numbers"/> 

Answer 3

@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 

    // Set the content of the activity to use the activity_main.xml layout file 
    setContentView(R.layout.activity_main); 

    // Find the View that shows the numbers category 
    TextView numbers = (TextView) findViewById(R.id.numbers); 

    // Set a click listener on that View 
    numbers.setOnClickListener(new View.OnClickListener() { 
    // The code in this method will be executed when the numbers View is clicked on. 

    @Override 
    public void onClick(View view) { 
     Intent numbersIntent = new Intent(MainActivity.this, Numbers.class); 
     startActivity(numbersIntent); 
    } 
} 

か：：

public class MainActivity extends AppCompatActivity implements OnClickListener{ 
    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 

     // Set the content of the activity to use the activity_main.xml layout file 
     setContentView(R.layout.activity_main); 

     // Find the View that shows the numbers category 
     TextView numbers = (TextView) findViewById(R.id.numbers); 

     // Set a click listener on that View 
     numbers.setOnClickListener(this); 
    } 

    @Override 
    public void onClick(View view) { 
     Intent numbersIntent = new Intent(MainActivity.this, Numbers.class); 
     startActivity(numbersIntent); 
    } 
}