Android的活動 - 從一個屏幕到另一個屏幕

Question

蔭新Android開發，我已經創建使用抽屜式導航的機器人滑動菜單按照本教程：http://www.androidhive.info/2013/11/android-sliding-menu-using-navigation-drawer/

我已經放置在主網頁上的按鈕（HomeFragment）的應用程序，我想鏈接到另一個活動/頁面（NewActivity）的按鈕。目前我收到很多錯誤。

MainActivity：

package info.androidhive.slidingmenu; 

import info.androidhive.slidingmenu.adapter.NavDrawerListAdapter; 
import info.androidhive.slidingmenu.model.NavDrawerItem; 

import java.util.ArrayList; 

import android.app.Activity; 
import android.app.Fragment; 
import android.app.FragmentManager; 
import android.content.res.Configuration; 
import android.content.res.TypedArray; 
import android.os.Bundle; 
import android.support.v4.app.ActionBarDrawerToggle; 
import android.support.v4.widget.DrawerLayout; 
import android.util.Log; 
import android.view.Menu; 
import android.view.MenuItem; 
import android.view.View; 
import android.widget.AdapterView; 
import android.widget.ListView; 

public class MainActivity extends Activity { 
    private DrawerLayout mDrawerLayout; 
    private ListView mDrawerList; 
    private ActionBarDrawerToggle mDrawerToggle; 

    // nav drawer title 
    private CharSequence mDrawerTitle; 

    // used to store app title 
    private CharSequence mTitle; 

    // slide menu items 
    private String[] navMenuTitles; 
    private TypedArray navMenuIcons; 

    private ArrayList<NavDrawerItem> navDrawerItems; 
    private NavDrawerListAdapter adapter; 

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

     mTitle = mDrawerTitle = getTitle(); 

     // load slide menu items 
     navMenuTitles = getResources().getStringArray(R.array.nav_drawer_items); 

     // nav drawer icons from resources 
     navMenuIcons = getResources() 
       .obtainTypedArray(R.array.nav_drawer_icons); 

     mDrawerLayout = (DrawerLayout) findViewById(R.id.drawer_layout); 
     mDrawerList = (ListView) findViewById(R.id.list_slidermenu); 

     navDrawerItems = new ArrayList<NavDrawerItem>(); 

     // adding nav drawer items to array 
     // Home 
     navDrawerItems.add(new NavDrawerItem(navMenuTitles[0], navMenuIcons.getResourceId(0, -1))); 
     // Find People 
     navDrawerItems.add(new NavDrawerItem(navMenuTitles[1], navMenuIcons.getResourceId(1, -1))); 
     // Photos 
     navDrawerItems.add(new NavDrawerItem(navMenuTitles[2], navMenuIcons.getResourceId(2, -1))); 
     // Communities, Will add a counter here 
     navDrawerItems.add(new NavDrawerItem(navMenuTitles[3], navMenuIcons.getResourceId(3, -1), true, "22")); 
     // Pages 
     navDrawerItems.add(new NavDrawerItem(navMenuTitles[4], navMenuIcons.getResourceId(4, -1))); 
     // What's hot, We will add a counter here 
     navDrawerItems.add(new NavDrawerItem(navMenuTitles[5], navMenuIcons.getResourceId(5, -1), true, "50+")); 


     // Recycle the typed array 
     navMenuIcons.recycle(); 

     mDrawerList.setOnItemClickListener(new SlideMenuClickListener()); 

     // setting the nav drawer list adapter 
     adapter = new NavDrawerListAdapter(getApplicationContext(), 
       navDrawerItems); 
     mDrawerList.setAdapter(adapter); 

     // enabling action bar app icon and behaving it as toggle button 
     getActionBar().setDisplayHomeAsUpEnabled(true); 
     getActionBar().setHomeButtonEnabled(true); 

     mDrawerToggle = new ActionBarDrawerToggle(this, mDrawerLayout, 
       R.drawable.ic_drawer, //nav menu toggle icon 
       R.string.app_name, // nav drawer open - description for accessibility 
       R.string.app_name // nav drawer close - description for accessibility 
     ) { 
      public void onDrawerClosed(View view) { 
       getActionBar().setTitle(mTitle); 
       // calling onPrepareOptionsMenu() to show action bar icons 
       invalidateOptionsMenu(); 
      } 

      public void onDrawerOpened(View drawerView) { 
       getActionBar().setTitle(mDrawerTitle); 
       // calling onPrepareOptionsMenu() to hide action bar icons 
       invalidateOptionsMenu(); 
      } 
     }; 
     mDrawerLayout.setDrawerListener(mDrawerToggle); 

     if (savedInstanceState == null) { 
      // on first time display view for first nav item 
      displayView(0); 
     } 
    } 

    /** 
    * Slide menu item click listener 
    * */ 
    private class SlideMenuClickListener implements 
      ListView.OnItemClickListener { 
     @Override 
     public void onItemClick(AdapterView<?> parent, View view, int position, 
       long id) { 
      // display view for selected nav drawer item 
      displayView(position); 
     } 
    } 

    @Override 
    public boolean onCreateOptionsMenu(Menu menu) { 
     getMenuInflater().inflate(R.menu.main, menu); 
     return true; 
    } 

    @Override 
    public boolean onOptionsItemSelected(MenuItem item) { 
     // toggle nav drawer on selecting action bar app icon/title 
     if (mDrawerToggle.onOptionsItemSelected(item)) { 
      return true; 
     } 
     // Handle action bar actions click 
     switch (item.getItemId()) { 
     case R.id.action_settings: 
      return true; 
     default: 
      return super.onOptionsItemSelected(item); 
     } 
    } 

    /* * 
    * Called when invalidateOptionsMenu() is triggered 
    */ 
    @Override 
    public boolean onPrepareOptionsMenu(Menu menu) { 
     // if nav drawer is opened, hide the action items 
     boolean drawerOpen = mDrawerLayout.isDrawerOpen(mDrawerList); 
     menu.findItem(R.id.action_settings).setVisible(!drawerOpen); 
     return super.onPrepareOptionsMenu(menu); 
    } 

    /** 
    * Diplaying fragment view for selected nav drawer list item 
    * */ 
    private void displayView(int position) { 
     // update the main content by replacing fragments 
     Fragment fragment = null; 
     switch (position) { 
     case 0: 
      fragment = new HomeFragment(); 
      break; 
     case 1: 
      fragment = new FindPeopleFragment(); 
      break; 
     case 2: 
      fragment = new PhotosFragment(); 
      break; 
     case 3: 
      fragment = new CommunityFragment(); 
      break; 
     case 4: 
      fragment = new PagesFragment(); 
      break; 
     case 5: 
      fragment = new WhatsHotFragment(); 
      break; 

     default: 
      break; 
     } 

     if (fragment != null) { 
      FragmentManager fragmentManager = getFragmentManager(); 
      fragmentManager.beginTransaction() 
        .replace(R.id.frame_container, fragment).commit(); 

      // update selected item and title, then close the drawer 
      mDrawerList.setItemChecked(position, true); 
      mDrawerList.setSelection(position); 
      setTitle(navMenuTitles[position]); 
      mDrawerLayout.closeDrawer(mDrawerList); 
     } else { 
      // error in creating fragment 
      Log.e("MainActivity", "Error in creating fragment"); 
     } 
    } 

    @Override 
    public void setTitle(CharSequence title) { 
     mTitle = title; 
     getActionBar().setTitle(mTitle); 
    } 

    /** 
    * When using the ActionBarDrawerToggle, you must call it during 
    * onPostCreate() and onConfigurationChanged()... 
    */ 

    @Override 
    protected void onPostCreate(Bundle savedInstanceState) { 
     super.onPostCreate(savedInstanceState); 
     // Sync the toggle state after onRestoreInstanceState has occurred. 
     mDrawerToggle.syncState(); 
    } 

    @Override 
    public void onConfigurationChanged(Configuration newConfig) { 
     super.onConfigurationChanged(newConfig); 
     // Pass any configuration change to the drawer toggls 
     mDrawerToggle.onConfigurationChanged(newConfig); 
    } 

} 

HomeFragment：

package info.androidhive.slidingmenu; 

import android.app.Fragment; 
import android.content.Intent; 
import android.os.Bundle; 
import android.view.LayoutInflater; 
import android.view.View; 
import android.view.View.OnClickListener; 
import android.view.ViewGroup; 
import android.widget.Button; 

public class HomeFragment extends Fragment implements OnClickListener{ 
    private Button button; 
    public HomeFragment(){} 

    @Override 

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

     View rootView = inflater.inflate(R.layout.fragment_home, container, false); 

     Button b = (Button) rootView.findViewById(R.id.button1); 
     b.setOnClickListener(this); 

     return rootView; 
    } 

    public void onClick(View v) { 

     switch (v.getId()) { 
     case R.id.button1: 

      Intent intent = new Intent(getActivity(), NewActivity.class); 
      startActivity(intent); 

      System.out.println("Hi its me"); 
      break; 
     } 
    } 

} 

NewActivity：

package info.androidhive.slidingmenu; 

import android.os.Bundle; 
import android.app.Activity; 

public class NewActivity extends Activity { 

    @Override 
    public void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     // Get the view from new_activity.xml 
     setContentView(R.layout.new_activity); 
    } 
} 

AndroidManifest：

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

    <uses-sdk 
     android:minSdkVersion="11" 
     android:targetSdkVersion="17" /> 

    <application 
     android:allowBackup="true" 
     android:icon="@drawable/ic_launcher" 
     android:label="@string/app_name" 
     android:theme="@style/AppTheme" > 
     <activity 
      android:name="info.androidhive.slidingmenu.MainActivity" 
      android:label="@string/app_name" > 
      <intent-filter> 
       <action android:name="android.intent.action.MAIN" /> 

       <category android:name="android.intent.category.LAUNCHER" /> 
      </intent-filter> 
     </activity> 

     <activity android:name=".NewActivity" > 
    </activity> 

    </application> 

</manifest> 

fragment_home.xml：

<?xml version="1.0" encoding="utf-8"?> 
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" 
    android:layout_width="match_parent" 
    android:layout_height="match_parent" > 

    <TextView 
     android:id="@+id/txtLabel" 
     android:layout_width="wrap_content" 
     android:layout_height="wrap_content" 
     android:layout_centerInParent="true" 
     android:text="Home View" 
     android:textSize="16dp" /> 

    <ImageView 
     android:id="@+id/imageView1" 
     android:layout_width="wrap_content" 
     android:layout_height="wrap_content" 
     android:layout_below="@id/txtLabel" 
     android:layout_centerHorizontal="true" 
     android:layout_marginTop="10dp" 
     android:src="@drawable/ic_home" /> 

    <Button 
     android:id="@+id/button1" 
     android:layout_width="wrap_content" 
     android:layout_height="wrap_content" 
     android:layout_alignLeft="@+id/imageView1" 
     android:layout_alignParentTop="true" 
     android:layout_marginTop="56dp" 
     android:text="Button" 
     android:text="Button" /> 

</RelativeLayout> 

的logcat：

12-03 20:28:26.823: E/Trace(1373): error opening trace file: No such file or directory (2) 
12-03 20:28:27.134: D/dalvikvm(1373): GC_FOR_ALLOC freed 84K, 8% free 2608K/2816K, paused 38ms, total 46ms 
12-03 20:28:27.134: I/dalvikvm-heap(1373): Grow heap (frag case) to 3.269MB for 635812-byte allocation 
12-03 20:28:27.184: D/dalvikvm(1373): GC_FOR_ALLOC freed 2K, 7% free 3226K/3440K, paused 49ms, total 49ms 
12-03 20:28:27.276: D/dalvikvm(1373): GC_CONCURRENT freed <1K, 6% free 3261K/3440K, paused 4ms+62ms, total 89ms 
12-03 20:28:27.284: D/AndroidRuntime(1373): Shutting down VM 
12-03 20:28:27.284: W/dalvikvm(1373): threadid=1: thread exiting with uncaught exception (group=0x40a71930) 
12-03 20:28:27.314: E/AndroidRuntime(1373): FATAL EXCEPTION: main 
12-03 20:28:27.314: E/AndroidRuntime(1373): java.lang.RuntimeException: Unable to start activity ComponentInfo{info.androidhive.slidingmenu/info.androidhive.slidingmenu.MainActivity}: java.lang.NullPointerException 
12-03 20:28:27.314: E/AndroidRuntime(1373):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2180) 
12-03 20:28:27.314: E/AndroidRuntime(1373):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230) 
12-03 20:28:27.314: E/AndroidRuntime(1373):  at android.app.ActivityThread.access$600(ActivityThread.java:141) 
12-03 20:28:27.314: E/AndroidRuntime(1373):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234) 
12-03 20:28:27.314: E/AndroidRuntime(1373):  at android.os.Handler.dispatchMessage(Handler.java:99) 
12-03 20:28:27.314: E/AndroidRuntime(1373):  at android.os.Looper.loop(Looper.java:137) 
12-03 20:28:27.314: E/AndroidRuntime(1373):  at android.app.ActivityThread.main(ActivityThread.java:5041) 
12-03 20:28:27.314: E/AndroidRuntime(1373):  at java.lang.reflect.Method.invokeNative(Native Method) 
12-03 20:28:27.314: E/AndroidRuntime(1373):  at java.lang.reflect.Method.invoke(Method.java:511) 
12-03 20:28:27.314: E/AndroidRuntime(1373):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793) 
12-03 20:28:27.314: E/AndroidRuntime(1373):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560) 
12-03 20:28:27.314: E/AndroidRuntime(1373):  at dalvik.system.NativeStart.main(Native Method) 
12-03 20:28:27.314: E/AndroidRuntime(1373): Caused by: java.lang.NullPointerException 
12-03 20:28:27.314: E/AndroidRuntime(1373):  at info.androidhive.slidingmenu.HomeFragment.onCreateView(HomeFragment.java:23) 
12-03 20:28:27.314: E/AndroidRuntime(1373):  at android.app.Fragment.performCreateView(Fragment.java:1695) 
12-03 20:28:27.314: E/AndroidRuntime(1373):  at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:885) 
12-03 20:28:27.314: E/AndroidRuntime(1373):  at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:1057) 
12-03 20:28:27.314: E/AndroidRuntime(1373):  at android.app.BackStackRecord.run(BackStackRecord.java:682) 
12-03 20:28:27.314: E/AndroidRuntime(1373):  at android.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1435) 
12-03 20:28:27.314: E/AndroidRuntime(1373):  at android.app.Activity.performStart(Activity.java:5113) 
12-03 20:28:27.314: E/AndroidRuntime(1373):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2153) 
12-03 20:28:27.314: E/AndroidRuntime(1373):  ... 11 more 

修訂：

現在一切工作正常，上面的代碼更新。我通過在HomeFragment中使用「intent」解決了這個問題，另外我在宣言中添加了一個新的活動。

Answer 1

看第二行的位置：

12-03 20:28:27.314: E/AndroidRuntime(1373): Caused by: java.lang.NullPointerException 
12-03 20:28:27.314: E/AndroidRuntime(1373):  at info.androidhive.slidingmenu.HomeFragment.onCreateView(HomeFragment.java:23) 
12-03 20:28:27.314: E/AndroidRuntime(1373):  at android.app.Fragment.performCreateView(Fragment.java:1695) 
12-03 20:28:27.314: E/AndroidRuntime(1373):  at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:885) 

有一個在HomeFragment.java一個NullPointerException 23行：

Button b = (Button) rootView.findViewById(R.id.button1); 
    b.setOnClickListener(this); // line 23 

可能導致此那裏唯一是b是null。 如果R.layout.fragment_home不包含ID爲button1的元素，可能會發生這種情況。

這就是你需要解決的問題。

如果你有在這之後其他的問題，請按照同樣的技術：

1. 獲取堆棧跟蹤
2. 尋找在堆棧跟蹤的第一行這是一個從自己的代碼來
3. 弄清楚發生了什麼錯誤的行和進行必要的更正