我可以使用本机后退按钮在我的应用程序中前进和后退。如果我使用触摸按钮，应用程序将通过附加的Stacktrace停止。
只在一个视图中，它包含一个WebView。我不想像所有其他人一样为WebView实现一个后退按钮，他们在这里提出了类似的问题（回页而不是活动回来）。
我还附上了应用程序的一些代码。它会在活动加载额外内容时崩溃（NullPointerException）。我可以避免，后退按钮会创建一个全新的活动吗？在我的应用程序的其他部分，这工作没有问题，即使有额外的移交
我尝试了什么： 使用Bundle并将附加内容直接放入intent中。
堆栈跟踪：
08-18 22:52:04.308 6982-6982/com.nubage.minepedia E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: com.nubage.minepedia, PID: 6982
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.nubage.minepedia/com.nubage.minepedia.ItemsView}: java.lang.NullPointerException
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2215)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2265)
at android.app.ActivityThread.access$800(ActivityThread.java:145)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1206)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:136)
at android.app.ActivityThread.main(ActivityThread.java:5081)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:791)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:607)
at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.NullPointerException
at com.nubage.minepedia.ItemsView.onCreate(ItemsView.java:36)
at android.app.Activity.performCreate(Activity.java:5231)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2169)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2265)
at android.app.ActivityThread.access$800(ActivityThread.java:145)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1206)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:136)
at android.app.ActivityThread.main(ActivityThread.java:5081)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:791)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:607)
at dalvik.system.NativeStart.main(Native Method)
ItemsMenu：
public class ItemsMenu extends Activity {
private final String MENU_NAME = "items";
private final String KEY_CATEGORY = "category";
private final String KEY_SUBCATEGORY = "subcategory";
// .....
public void itemButtonClicked(View view) {
String parameter = null;
Log.d("ID: ", String.valueOf(view.getId()));
switch (view.getId()) {
case R.id.building_blocks_id:
parameter = getString(R.string.building_blocks);
break;
case R.id.decoration_blocks_id:
parameter = getString(R.string.decoration_blocks);
break;
case R.id.redstone_id:
parameter = getString(R.string.redstone);
break;
case R.id.transportation_id:
parameter = getString(R.string.transportation);
break;
case R.id.miscellaneous_id:
parameter = getString(R.string.miscellaneous);
break;
case R.id.foodstuffs_id:
parameter = getString(R.string.foodstuffs);
break;
case R.id.tools_id:
parameter = getString(R.string.tools);
break;
case R.id.combat_id:
parameter = getString(R.string.combat);
break;
case R.id.brewing_id:
parameter = getString(R.string.brewing);
break;
case R.id.materials_id:
parameter = getString(R.string.materials);
break;
}
Log.d("ItemsMenu - itemButtonClicked() parameter: ", parameter);
if (parameter != null) {
Intent itemsView = new Intent(this, ItemsView.class);
Bundle bundle = new Bundle();
bundle.putString(KEY_CATEGORY, MENU_NAME);
bundle.putString(KEY_SUBCATEGORY, parameter);
itemsView.putExtras(bundle);
startActivity(itemsView);
}
}
}
ItemsView.class：
public class ItemsView extends Activity {
private final String MENU_NAME = "items";
private final String KEY_CATEGORY = "category";
private final String KEY_SUBCATEGORY = "subcategory";
GridView gridView;
GridViewCustomAdapter gridViewCustomAdapter;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_items_view);
String category = this.getIntent().getExtras().getString(KEY_CATEGORY);
String subcategory = this.getIntent().getExtras().getString(KEY_SUBCATEGORY);
/*if (this.getIntent().getExtras().getString(KEY_CATEGORY) != null)
this.category = this.getIntent().getExtras().getString(KEY_CATEGORY);
if (this.getIntent().getExtras().getString(KEY_SUBCATEGORY) != null)
this.subcategory = this.getIntent().getExtras().getString(KEY_SUBCATEGORY);
*/
Log.d("ItemsView - onCreate() - Bundle Category: " + category, "Length: " + category.length());
Log.d("ItemsView - onCreate() - Bundle Category: " + subcategory, "Length: " + subcategory.length());
// String[] databaseArray = new String[Minepedia_main.database.size()];
// for (int i=0; i<Minepedia_main.database.size(); ++i)
// databaseArray[i] = Minepedia_main.database.get(i);
//Search the Database for wanted entries...
List<String> resultCollection = new ArrayList<String>(150);
for (int i=0; i<Minepedia_main.database.size(); ++i) {
String temp = Minepedia_main.database.get(i);
String[] split = temp.split(Pattern.quote("|"));
if (split[2].equals(category) && split[3].equals(subcategory)) {
resultCollection.add(temp);
}
/*if (temp.contains(category) && temp.contains(subcategory)) {
resultCollection.add(temp);
}*/
}
//List to Array...
final String[] databaseArray = new String[resultCollection.size()];
for (int i=0; i<resultCollection.size(); ++i) {
databaseArray[i] = resultCollection.get(i);
}
gridView = (GridView)findViewById(R.id.gridView1);
// Set the Adapter to GridView
gridView.setAdapter(new GridViewCustomAdapter(this, databaseArray));
// Handling touch/click Event on GridView Item
gridView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> arg0, View v, int position, long arg3) {
if (Minepedia_main.ONLINE_MODE_ENABLED == false) {
String fileName = databaseArray[position].split(Pattern.quote("|"))[0] + ".html";
createOfflineIntent(fileName);
} else {
String url = Minepedia_main.PROVIDER + databaseArray[position].split(Pattern.quote("|"))[4];
createOnlineIntent(url);
}
}
});
}
private void createOfflineIntent(String fileName) {
Intent offlineBrowser = new Intent(this, ItemViewDetailOffline.class);
//offlineBrowser.putExtra("fileName", fileName);
Bundle bundle = new Bundle();
bundle.putString("fileName", fileName);
offlineBrowser.putExtras(bundle);
startActivity(offlineBrowser);
}
private void createOnlineIntent(String url) {
Intent onlineBrowser = new Intent(this, ItemViewDetailOnline.class);
//onlineBrowser.putExtra("url", url);
Bundle bundle = new Bundle();
bundle.putString("url", url);
onlineBrowser.putExtras(bundle);
startActivity(onlineBrowser);
}
}
ItemViewDetailOnline.class：
public class ItemViewDetailOnline extends Activity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_item_view_detail_online);
String url = this.getIntent().getExtras().getString("url");
WebView webview = (WebView) findViewById(R.id.webview_online);
webview.loadUrl(url);
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.item_view_detail, 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);
}
}
activity_item_view_detail_online.xml：
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
android:paddingBottom="@dimen/activity_vertical_margin"
tools:context="com.nubage.minepedia.ItemViewDetailOnline">
<TextView
android:text="@string/hello_world"
android:layout_width="wrap_content"
android:layout_height="wrap_content" />
<WebView
android:id="@+id/webview_online"
android:layout_width="match_parent"
android:layout_height="wrap_content"/>
</LinearLayout>