为什么“OnClickListener”无法正常工作

Question

我不明白为什么这个简单的代码不起作用。
此代码假设将按钮文本的颜色设置为蓝色，就这些了。 我只添加到一个新创建的项目行：

final Button btn = (Button) findViewById(R.id.button1); 
    btn.setOnClickListener(new View.OnClickListener() { 
    @Override 
    public void onClick(View v) { 
      // Perform action on click 
      btn.setTextColor(Color.BLUE); 
     } 
    }); 

的完整代码：

package com.example.b; 

import android.graphics.Color; 
import android.os.Bundle; 
import android.support.v4.app.Fragment; 
import android.support.v7.app.ActionBarActivity; 
import android.view.LayoutInflater; 
import android.view.Menu; 
import android.view.MenuItem; 
import android.view.View; 
import android.view.ViewGroup; 
import android.widget.Button; 

public class MainActivity extends ActionBarActivity { 

protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_main); 

    final Button btn = (Button) findViewById(R.id.button1); 
    btn.setOnClickListener(new View.OnClickListener() { 
    @Override 
    public void onClick(View v) { 
      // Perform action on click 
      btn.setTextColor(Color.BLUE); 
     } 
    }); 

    if (savedInstanceState == null) { 
     getSupportFragmentManager().beginTransaction() 
       .add(R.id.container, new PlaceholderFragment()) 
       .commit(); 
    } 
} 


@Override 
public boolean onCreateOptionsMenu(Menu menu) { 

    // Inflate the menu; this adds items to the action bar if it is present. 
    getMenuInflater().inflate(R.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(); 
    if (id == R.id.action_settings) { 
     return true; 
    } 
    return super.onOptionsItemSelected(item); 
} 

/** 
* A placeholder fragment containing a simple view. 
*/ 
public static class PlaceholderFragment extends Fragment { 

    public PlaceholderFragment() { 
    } 

    @Override 
    public View onCreateView(LayoutInflater inflater, ViewGroup container, 
      Bundle savedInstanceState) { 
     View rootView = inflater.inflate(R.layout.fragment_main, container, false); 
     return rootView; 
    } 
} 

} 

Answer 1

最有可能的按钮在片段，而不是活动。如果是这样，请将您的findViewById和您的setonclick代码移到您的PlaceHolderFragment中。