Java方法 - 缺少返回语句

Question

所以我发现了很多这个问题的例子，但解决它的方法似乎有所不同。所以在这里我正在寻找解决我的具体问题。

这里是我的代码：

package com.example.frederik.snapsule; 

import android.app.Activity; 
import android.os.Bundle; 
import android.view.LayoutInflater; 
import android.view.View; 
import android.view.ViewGroup; 
import android.widget.TextView; 

import com.facebook.CallbackManager; 
import com.facebook.FacebookCallback; 
import com.facebook.FacebookException; 
import com.facebook.FacebookSdk; 
import com.facebook.login.LoginResult; 
import com.facebook.login.widget.LoginButton; 

public class MainActivity extends Activity { 

    LoginButton login; 
    TextView info; 
    CallbackManager callbackManager; 

    //Creating and initializing the feature(Code from Facebook install guide) 
    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     FacebookSdk.sdkInitialize(getApplicationContext()); //Calls for the facebook feature 
    } 

    @Override 
    public View onCreateView(
      LayoutInflater inflater, 
      ViewGroup container, 
      Bundle savedInstanceState) { 
     View view = inflater.inflate(R.layout.content_main, container, false); 

     login = (LoginButton) view.findViewById(R.id.login_button); 
     login.setReadPermissions("user_friends"); 

     // Callback registration 
     login.registerCallback(callbackManager, new FacebookCallback<LoginResult>() { 
      @Override 
      public void onSuccess(LoginResult loginResult) { 
       // App code 
      } 

      @Override 
      public void onCancel() { 
       // App code 
      } 

      @Override 
      public void onError(FacebookException exception) { 
       // App code 
      } 
     }); 
    } 
} 

在倒数第二个“}”我的错误“缺少return语句”，但我的眼睛似乎是正确的。

Answer 1

OncreateView有返回类型的View，所以你必须返回其连接到活动视图。

如果您是覆盖onCreate方法，您可能不需要覆盖OnCreateView方法。在onCreate方法中您可以使用setContentView(R.layout.content_main)。

@Override 
public View onCreateView(LayoutInflater inflater,ViewGroup container,Bundle savedInstanceState) { 

    View view = inflater.inflate(R.layout.content_main, container, false); 

    login = (LoginButton) view.findViewById(R.id.login_button); 
    login.setReadPermissions("user_friends"); 

    // Callback registration 
    login.registerCallback(callbackManager, new FacebookCallback<LoginResult>() { 
     @Override 
     public void onSuccess(LoginResult loginResult) { 
      // App code 
     } 

     @Override 
     public void onCancel() { 
      // App code 
     } 

     @Override 
     public void onError(FacebookException exception) { 
      // App code 
     } 
    }); 
    /** 
    *return view 
    */ 
    return view; 
} 

Answer 2

解决此错误的方法始终是相同的：当方法具有返回类型并且并非所有代码路径都返回该类型的值时发生该错误。 onCreateView方法应该返回一个View，在你的情况下它不会。你是膨胀变成了view变量的视图，但你永远不会返回那个值。如下面的陈述

@Override 
public View onCreateView(
     LayoutInflater inflater, 
     ViewGroup container, 
     Bundle savedInstanceState) { 
    View view = inflater.inflate(R.layout.content_main, container, false); 

    login = (LoginButton) view.findViewById(R.id.login_button); 
    login.setReadPermissions("user_friends"); 

    // Callback registration 
    login.registerCallback(callbackManager, new FacebookCallback<LoginResult>() { 
     @Override 
     public void onSuccess(LoginResult loginResult) { 
      // App code 
     } 

     @Override 
     public void onCancel() { 
      // App code 
     } 

     @Override 
     public void onError(FacebookException exception) { 
      // App code 
     } 
    }); 

    return view; // <<< THIS IS IT 
} 

Answer 3

添加return语句：

@Override 
public View onCreateView(
     LayoutInflater inflater, 
     ViewGroup container, 
     Bundle savedInstanceState) { 
    View view = inflater.inflate(R.layout.content_main, container, false); 

    login = (LoginButton) view.findViewById(R.id.login_button); 
    login.setReadPermissions("user_friends"); 

    // Callback registration 
    login.registerCallback(callbackManager, new FacebookCallback<LoginResult>() { 
     @Override 
     public void onSuccess(LoginResult loginResult) { 
      // App code 
     } 

     @Override 
     public void onCancel() { 
      // App code 
     } 

     @Override 
     public void onError(FacebookException exception) { 
      // App code 
     } 
    }); 
    return view;//view must be returned from this method 
} 

Answer 4

先加这个return view;

@Override 
     public void onError(FacebookException exception) { 
      // App code 
     } 
    }); 
    return view;//Add this 
} 

哪里是的setContentView

更改您的代码？

http://developer.android.com/intl/es/reference/android/app/Activity.html#setContentView(android.view.View)

@Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.your_layout); 
     FacebookSdk.sdkInitialize(getApplicationContext()); //Calls for the facebook feature 
    }