Android的问题：能解释一下else里边的onBackPressed()方法是返回到哪里去吗？

Posted 2023-03-22

public boolean onKeyDown(int keyCode, KeyEvent event)
if (checkNetWorkStatus())
if ((keyCode == KeyEvent.KEYCODE_BACK) && webView.canGoBack())
webView.goBack(); // goBack()表示返回WebView的上一页面
return true;

else
onBackPressed();

return super.onKeyDown(keyCode, event);

参考技术A 看下源码，最终还是调用到finish()，finish() 调用的底层C/C++方法，
/**

* Called when the activity has detected the user's press of the back

* key. The default implementation simply finishes the current activity,

* but you can override this to do whatever you want.

*/

public void onBackPressed()

if (mActionBar != null && mActionBar.collapseActionView())

return;



if (!mFragments.popBackStackImmediate())

finishAfterTransition();





/**

* Reverses the Activity Scene entry Transition and triggers the calling Activity

* to reverse its exit Transition. When the exit Transition completes,

* @link #finish() is called. If no entry Transition was used, finish() is called

* immediately and the Activity exit Transition is run.

* @see android.app.ActivityOptions#makeSceneTransitionAnimation(Activity, android.util.Pair[])

*/
public void finishAfterTransition()

if (!mActivityTransitionState.startExitBackTransition(this))

finish();



追问

……看不懂

追答

。。。。。。。。。。。。。这么简单哪里看不懂。。。。

追问

……就是还是没弄懂它返回到哪个页面的

追答

返回上一个喽， webview内部还需要解决 http://blog.csdn.net/t12x3456/article/details/39134961

本回答被提问者和网友采纳 参考技术B 此次擦擦擦擦擦擦擦擦擦擦擦擦擦擦擦擦擦擦擦擦擦擦擦擦

我的代码出错了，谁能解释一下怎么回事？

【中文标题】我的代码出错了，谁能解释一下怎么回事？

【英文标题】：Error in my code, can anyone explain whats wrong?

【发布时间】：2014-03-21 00:44:20

【问题描述】：

我是 C++ 新手，我正在开发一个程序，但在第 39 行它显示错误“else”，没有先前的“if”，但我确实有一个先前的 if。有人对我做错了什么有任何意见吗？这是我的程序代码。谢谢。

1 #include <fstream>
2 #include <iostream>
3 #include <cstdlib>
4 using namespace std;
5 int main()
6  
7 //Declarations
8     ifstream masterFile;
9     ifstream transactionFile;
10    ofstream newMasterFile;
11    double mClientNumber, mtotalClientCost, tClientNumber, titemClientCost;
12    string mClientfName, mClientlName;
13 cout << "Master File Updating Starting" ;
14 masterFile.open("Master.rtf");
15 transactionFile.open("Transaction.rtf");
16 newMasterFile.open("newMaster.rtf");
17 masterFile >> mClientNumber;
18 masterFile >> mClientfName;
19 masterFile >> mClientlName;
20 masterFile >> mtotalClientCost;
21 transactionFile >> tClientNumber;
22 transactionFile >>titemClientCost;
23 while ( transactionFile.eof() )
24 
25     while (( masterFile.eof()) && (mClientNumber < tClientNumber))
26     
27         newMasterFile << mClientNumber << endl;
28         newMasterFile << mClientfName << endl;
29         newMasterFile << mClientlName << endl;
30         newMasterFile << mtotalClientCost << endl;
31         masterFile >> mClientNumber;
32         masterFile >> mClientfName;
33         masterFile >> mClientlName;
34         masterFile >> mtotalClientCost;
35     
36     if (masterFile.eof());
37    
38         cout << "Error Client ID: " << tClientNumber << " not in Master File." ;
39     else if (mClientNumber == tClientNumber);
40         mtotalClientCost = mtotalClientCost + titemClientCost;
41         newMasterFile << mClientNumber << endl;
42         newMasterFile << mClientfName << endl;
43         newMasterFile << mClientlName << endl;
44         newMasterFile << mtotalClientCost << endl;
45         masterFile >> mClientNumber;
46         masterFile >> mClientfName;
47         masterFile >> mClientlName;
48         masterFile >> mtotalClientCost;
49     else if (mClientNumber > tClientNumber);
50         cout << "Error Client ID: " << tClientNumber << " not in Master File." ;
51     
52     transactionFile >> tClientNumber;
53     transactionFile >> titemClientCost;
54 
55 while (masterFile.eof())
56 
57         newMasterFile << mClientNumber << endl;
58         newMasterFile << mClientfName << endl;
59         newMasterFile << mClientlName << endl;
60         newMasterFile << mtotalClientCost << endl;
61         masterFile >> mClientNumber;
62         masterFile >> mClientfName;
63         masterFile >> mClientlName;
64         masterFile >> mtotalClientCost;
65 
66 cout << "Master File Updating Complete" ;
67
68 masterFile.close();
69 transactionFile.close();
70 newMasterFile.close();
71
72   system("pause");
73   return 0;
74 

【问题讨论】：

这不是你的问题，但你可能会觉得这很有趣***.com/questions/5605125/…

【参考方案1】：

if (masterFile.eof());
                  //^^this ; here effectively terminates your if block and 
                 //does not have a closing  before else

类似的问题可以在这里找到：

if (mClientNumber == tClientNumber);
                                //^^another line below same problem

【讨论】：

分号是多余的。它终止 if 语句。

@sj0h 是的，确切地说。我会更新措辞，谢谢！

【参考方案2】：

在所有 if 语句中，您添加了一个不必要的 ;。

if (masterFile.eof());
//                   ^ this semicolon is not supposed to be there

; 将终止 if 语句。

改为这样做：

if (masterFile.eof())

此外，您没有关闭 if 语句中的第一个括号。所以最终的产品应该是这样的：

if (masterFile.eof())
    //if body
else if (*next condition*)
    //else if body

等等..干杯

【参考方案3】：

首先你在 if 和 else if 语句之后放置了一个分号

if (masterFile.eof());

else if (mClientNumber == tClientNumber);

替换它们。

如果不考虑这个错字 yjen，else if 没有前面的 if 语句。相反，它被放入封闭 if 语句的复合语句中

if (masterFile.eof());

     cout << "Error Client ID: " << tClientNumber << " not in Master File." ;
     else if (mClientNumber == tClientNumber);

也许你的意思是以下

if (masterFile.eof());

     cout << "Error Client ID: " << tClientNumber << " not in Master File." ;

else if (mClientNumber == tClientNumber);

或者

if (masterFile.eof());

     cout << "Error Client ID: " << tClientNumber << " not in Master File." ;
     if (mClientNumber == tClientNumber);

【参考方案4】：

您在少数地方忘记了 和。将第 36-51 行更改为

36    if (masterFile.eof())
37    
38         cout << "Error Client ID: " << tClientNumber << " not in Master File." ;
39     else if (mClientNumber == tClientNumber)
40         mtotalClientCost = mtotalClientCost + titemClientCost;
41         newMasterFile << mClientNumber << endl;
42         newMasterFile << mClientfName << endl;
43         newMasterFile << mClientlName << endl;
44         newMasterFile << mtotalClientCost << endl;
45         masterFile >> mClientNumber;
46         masterFile >> mClientfName;
47         masterFile >> mClientlName;
48         masterFile >> mtotalClientCost;
49      else if (mClientNumber > tClientNumber)
50         cout << "Error Client ID: " << tClientNumber << " not in Master File." ;
51     

【讨论】：

您忘记提及他/她将; 放置在错误的位置并终止了 if 语句。