RuntimeExpection無法實例化活動

Question

我是一名使用android的初學者，所以承擔我的知識缺乏 我正在開發一個項目，該項目一直工作正常，經過幾次小改動後，它開始給我一個RuntimeException unable to instantiate activity ComponentInfo{com.id11298775.exercise5/com.id11298775.excercise5.MainActivity}: java.lang.NullPointerException。我已經恢復了適配器中的小改動，但仍然無法運行該應用程序。 這裏是我的目錄下載：

我試圖弄清楚什麼是錯我的主要活動在相當長的時間，但對我來說似乎一切都很好，所以我想我失去了一些東西 這是我MainActivity類：

package com.id11298775.exercise5; 

// import statements are here 



public class MainActivity extends Activity { 

private final String URI = getString(R.string.URI); 

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

    // get the subject name 
    EditText subjectName = (EditText) findViewById(R.id.activity_main_subjectname_et); 
    // associate editText with the context menu 
    subjectName.setOnCreateContextMenuListener(this); 

} 

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

/** 
* code that executes according to the menu item that is clicked 
*/ 
@Override 
public boolean onOptionsItemSelected(MenuItem item) { 
    switch (item.getItemId()) { 
    // click help 
    case R.id.help: 
     help(); 
     return true; 
     // click exit 
    case R.id.exit: 
     finish(); 

    default: 
     return super.onOptionsItemSelected(item); 
    } 
} 

/** 
* when help is clicked this method will display a page related to the 
* subject number that is entered If no subject name is entered display the 
* general page of subjects of the handbook 
*/ 
public void help() { 
    EditText subjectNumber = (EditText) findViewById(R.id.activity_main_subjectnumber_et); 
    String number = subjectNumber.getText().toString(); 
    String url = URI + number; 

    Uri uriUrl = Uri.parse(url); 
    Intent launchBrowser = new Intent(Intent.ACTION_VIEW, uriUrl); 
    startActivity(launchBrowser); 
} 

/** 
* Inflate the context menu 
*/ 
@Override 
public void onCreateContextMenu(ContextMenu menu, View v, 
     ContextMenuInfo menuInfo) { 
    MenuInflater inflater = getMenuInflater(); 
    inflater.inflate(R.menu.context_menu, menu); 
    super.onCreateContextMenu(menu, v, menuInfo); 
} 

/** 
* code that executes according to the context menu item that is selected 
*/ 
@Override 
public boolean onContextItemSelected(MenuItem item) { 
    EditText nameEd = (EditText) findViewById(R.id.activity_main_subjectname_et); 
    switch (item.getItemId()) { 
    // capitalize is selected 
    case R.id.contextmenu_capitalize: 
     String subjectName = nameEd.getText().toString(); 
     String upperCase = subjectName.toUpperCase(); 
     nameEd.setText(upperCase); 
     return true; 
     // clear is selected 
    case R.id.contextmenu_clear: 
     nameEd.setText(""); 
     return true; 

    default: 
     return super.onContextItemSelected(item); 
    } 
} 

/** 
* methdo called when showList button is clicked 
* @param v 
*/ 
public void showListButtonClicked(View v) { 

    Intent intent = new Intent(MainActivity.this, SubjectList.class); 
    startActivity(intent); 
} 

} 

，這是我的清單：

<?xml version="1.0" encoding="utf-8"?> 
<manifest xmlns:android="http://schemas.android.com/apk/res/android" 
package="com.id11298775.exercise5" 
android:versionCode="1" 
android:versionName="1.0" > 

<uses-sdk 
    android:minSdkVersion="11" 
    android:targetSdkVersion="18" /> 

<application 
    android:allowBackup="true" 
    android:icon="@drawable/ic_launcher" 
    android:label="@string/app_name" 
    android:theme="@style/AppTheme" > 
    <activity 
     android:name="com.id11298775.exercise5.MainActivity" 
     android:label="@string/app_name" 
     android:theme="@android:style/Theme.Holo.Light"> 
     <intent-filter> 
      <action android:name="android.intent.action.MAIN" /> 

      <category android:name="android.intent.category.LAUNCHER" /> 
     </intent-filter> 
    </activity> 
    <activity android:name="com.id11298775.exercise5.SubjectList"></activity> 
</application> 

</manifest> 

任何人都熱衷於幫助我嗎？ 感謝您分享您的知識..

Answer 1

這很可能是你的問題：

private final String URI = getString(R.string.URI); 

離開內onCreate()方法的聲明，而是把方法調用：

private String uri; 

@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_main); 
    uri = getString(R.string.URI); 
}