我正在尝试实现TabHost FragmentActivity，但是当我运行应用程序时发生ClassCastException：无法转换为android.support.v4.app.Fragment。
我的项目已配置supportev4库，但无效。
我的活动从FragmentActivity扩展，但不起作用。
这是什么问题？
package br.com.teste.activity;
import java.util.HashMap;
import android.content.Context;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentActivity;
import android.support.v4.app.FragmentTransaction;
import android.view.LayoutInflater;
import android.view.View;
import android.widget.LinearLayout;
import android.widget.TabHost;
import android.widget.TabHost.TabContentFactory;
import android.widget.TabHost.TabSpec;
import br.com.teste.R;
public class MainFragmentActivity extends FragmentActivity implements TabHost.OnTabChangeListener {
private TabHost mTabHost;
private HashMap<String, TabInfo> mapTabInfo = new HashMap<String, TabInfo>();
private TabInfo mLastTab = null;
private class TabInfo {
private String tag;
private Class clss;
private Bundle args;
private Fragment fragment;
TabInfo(String tag, Class clazz, Bundle args) {
this.tag = tag;
this.clss = clazz;
this.args = args;
}
}
class TabFactory implements TabContentFactory {
private final Context mContext;
/**
*
* @param context
*/
public TabFactory(Context context) {
mContext = context;
}
/**
* (non-Javadoc)
*
* @see android.widget.TabHost.TabContentFactory#createTabContent(java.lang.String)
*/
public View createTabContent(String tag) {
View v = new View(mContext);
v.setMinimumWidth(0);
v.setMinimumHeight(0);
return v;
}
}
@Override
protected void onCreate(Bundle savedInstance)
{
super.onCreate(savedInstance);
setContentView(R.layout.maintabhost);
initializeTabHost(savedInstance);
if(savedInstance != null)
mTabHost.setCurrentTabByTag(savedInstance.getString("tab"));
}
@Override
protected void onSaveInstanceState(Bundle outState)
{
outState.putString("tab", mTabHost.getCurrentTabTag());
super.onSaveInstanceState(outState);
}
/**
* Inicializa as tabs
* @param args
*/
private void initializeTabHost(Bundle args)
{
mTabHost = (TabHost)findViewById(android.R.id.tabhost);
mTabHost.setup();
TabInfo tabInfo = null;
String tagTabDefaul = "pesquisar";
String tagTab;
TabSpec tabSpecLocal = null;
//Add tab1
tagTab = "pesquisar";
tabSpecLocal = this.mTabHost.newTabSpec(tagTab);
View viewPesquisa = LayoutInflater.from(this).inflate(
R.layout.tab_layout_view, null);
LinearLayout lPesquisa = (LinearLayout)viewPesquisa.findViewById(R.id.tabsLayout);
lPesquisa.setBackgroundDrawable(getResources().getDrawable(R.drawable.tab_pesquisa_background_selector));
tabSpecLocal.setIndicator(viewPesquisa);
tabInfo = new TabInfo(tagTab, MainActivity.class, args);
this.mapTabInfo.put(tabInfo.tag, tabInfo);
addTab(this, this.mTabHost, tabSpecLocal, tabInfo);
tagTab = "lines";
tabSpecLocal = this.mTabHost.newTabSpec(tagTab);
View viewLines = LayoutInflater.from(this).inflate(
R.layout.tab_layout_view, null);
LinearLayout lLines = (LinearLayout)viewLines.findViewById(R.id.tabsLayout);
lLinhas.setBackgroundDrawable(getResources().getDrawable(R.drawable.tab_lines_background_selector));
tabSpecLocal.setIndicator(viewLines);
tabInfo = new TabInfo(tagTab, ListLinesActivity.class, args);
this.mapTabInfo.put(tabInfo.tag, tabInfo);
addTab(this, this.mTabHost, tabSpecLocal, tabInfo);
//Adiciona tab de Fields
tagTab = "fields";
tabSpecLocal = this.mTabHost.newTabSpec(tagTab);
View viewFields = LayoutInflater.from(this).inflate(
R.layout.tab_layout_view, null);
LinearLayout lFields = (LinearLayout)viewFields.findViewById(R.id.tabsLayout);
lFields.setBackgroundDrawable(getResources().getDrawable(R.drawable.tab_fields_background_selector));
tabSpecLocal.setIndicator(viewFields);
tabInfo = new TabInfo(tagTab, ListFieldsActivity.class, args);
this.mapTabInfo.put(tabInfo.tag, tabInfo);
addTab(this, this.mTabHost, tabSpecLocal, tabInfo);
//Seta a tab default
this.onTabChanged(tagTabDefaul);
mTabHost.setOnTabChangedListener(this);
}
/**
* Adiciona as tab's
* @param activity
* @param tabHost
* @param tabSpec
* @param tabInfo
*/
private static void addTab(MainFragmentActivity activity, TabHost tabHost, TabSpec tabSpec, TabInfo tabInfo)
{
//Attach a tab view factory to ths spec
tabSpec.setContent(activity.new TabFactory(activity));
String tag = tabSpec.getTag();
//Verifica se já existe um fragmento para esta tab, provavelmente de uma ação anterior
//Se tiver, desativa o fragmento, porque seu estado inicial é para não apresentar
tabInfo.fragment = activity.getSupportFragmentManager().findFragmentByTag(tag);
if((tabInfo.fragment != null) && (tabInfo.fragment.isDetached()))
{
FragmentTransaction ft = activity.getSupportFragmentManager().beginTransaction();
ft.detach(tabInfo.fragment);
ft.commit();
activity.getSupportFragmentManager().executePendingTransactions();
}
tabHost.addTab(tabSpec);
}
public void onTabChanged(String tag)
{
TabInfo newTab = this.mapTabInfo.get(tag);
if(mLastTab != newTab)
{
FragmentTransaction ft = this.getSupportFragmentManager().beginTransaction();
if(mLastTab != null)
{
if(mLastTab.fragment != null)
{
ft.detach(mLastTab.fragment);
}
}
if(newTab != null)
{
if(newTab.fragment == null)
{
newTab.fragment = Fragment.instantiate(this, newTab.clss.getName(), newTab.args);
ft.add(R.id.realtabcontent, newTab.fragment, newTab.tag);
}
else
{
ft.attach(newTab.fragment);
}
}
mLastTab = newTab;
ft.commit();
this.getSupportFragmentManager().executePendingTransactions();
}
}
//Cria a tab com personalização de layout
/*
private static View createTabView(final Context context, final String text) {
View view = LayoutInflater.from(context).inflate(
R.layout.tab_layout_view, null);
TextView tv = (TextView) view.findViewById(R.id.tabsText);
tv.setText(text);
return view;
}
*/
}
已更新
我的logCat
09-05 01:57:07.655: D/dalvikvm(727): GC_CONCURRENT freed 347K, 5% free 9061K/9479K, paused 91ms+6ms, total 192ms
09-05 01:57:07.655: D/dalvikvm(727): WAIT_FOR_CONCURRENT_GC blocked 56ms
09-05 01:57:07.695: D/AndroidRuntime(727): Shutting down VM
09-05 01:57:07.705: W/dalvikvm(727): threadid=1: thread exiting with uncaught exception (group=0x40a13300)
09-05 01:57:07.745: E/AndroidRuntime(727): FATAL EXCEPTION: main
09-05 01:57:07.745: E/AndroidRuntime(727): java.lang.RuntimeException: Unable to start activity ComponentInfo{br.com.teste/br.com.teste.activity.MainFragmentActivity}: java.lang.ClassCastException: br.com.teste.activity.MainActivity cannot be cast to android.support.v4.app.Fragment
09-05 01:57:07.745: E/AndroidRuntime(727): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2059)
09-05 01:57:07.745: E/AndroidRuntime(727): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2084)
09-05 01:57:07.745: E/AndroidRuntime(727): at android.app.ActivityThread.access$600(ActivityThread.java:130)
09-05 01:57:07.745: E/AndroidRuntime(727): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1195)
09-05 01:57:07.745: E/AndroidRuntime(727): at android.os.Handler.dispatchMessage(Handler.java:99)
09-05 01:57:07.745: E/AndroidRuntime(727): at android.os.Looper.loop(Looper.java:137)
09-05 01:57:07.745: E/AndroidRuntime(727): at android.app.ActivityThread.main(ActivityThread.java:4745)
09-05 01:57:07.745: E/AndroidRuntime(727): at java.lang.reflect.Method.invokeNative(Native Method)
09-05 01:57:07.745: E/AndroidRuntime(727): at java.lang.reflect.Method.invoke(Method.java:511)
09-05 01:57:07.745: E/AndroidRuntime(727): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
09-05 01:57:07.745: E/AndroidRuntime(727): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
09-05 01:57:07.745: E/AndroidRuntime(727): at dalvik.system.NativeStart.main(Native Method)
09-05 01:57:07.745: E/AndroidRuntime(727): Caused by: java.lang.ClassCastException: br.com.teste.activity.MainActivity cannot be cast to android.support.v4.app.Fragment
09-05 01:57:07.745: E/AndroidRuntime(727): at android.support.v4.app.Fragment.instantiate(Fragment.java:402)
09-05 01:57:07.745: E/AndroidRuntime(727): at br.com.teste.activity.MainFragmentActivity.onTabChanged(MainFragmentActivity.java:208)
09-05 01:57:07.745: E/AndroidRuntime(727): at br.com.teste.activity.MainFragmentActivity.initializeTabHost(MainFragmentActivity.java:159)
09-05 01:57:07.745: E/AndroidRuntime(727): at br.com.teste.activity.MainFragmentActivity.onCreate(MainFragmentActivity.java:75)
09-05 01:57:07.745: E/AndroidRuntime(727): at android.app.Activity.performCreate(Activity.java:5008)
09-05 01:57:07.745: E/AndroidRuntime(727): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1079)
09-05 01:57:07.745: E/AndroidRuntime(727): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2023)
09-05 01:57:07.745: E/AndroidRuntime(727): ... 11 more
答案 0 :(得分：1)
在initializeTabHost(Bundle)方法中，您正在使用MainActivity类创建新的TabInfo对象，然后在Fragment方法中使用相同的类实例化onTabChanged(String)。您需要MainActivity扩展Fragment，然后实例化newTab.clss并将其强制转换为片段。
编辑：添加了班级类型的验证
public void onTabChanged(String tag)
{
TabInfo newTab = this.mapTabInfo.get(tag);
if(mLastTab != newTab)
{
FragmentTransaction ft = this.getSupportFragmentManager().beginTransaction();
if(mLastTab != null)
{
if(mLastTab.fragment != null)
{
ft.detach(mLastTab.fragment);
}
}
if(newTab != null)
{
if(newTab.fragment == null)
{
Object objFragment = null;
try {
objFragment = Class.forName(newTab.clss.getName()).newInstance();
} catch (InstantiationException e) {
e.printStackTrace();
} catch (IllegalAccessException e) {
e.printStackTrace();
} catch (ClassNotFoundException e) {
e.printStackTrace();
}
if (! (objFragment instanceof Fragment))
{
Log.e("MainFragmentActivity", "Unable to cast " + newTab.clss.toString() + " to Fragment!");
return;
}
newTab.fragment = (Fragment) objFragment;
newTab.fragment.setArguments(newTab.args);
ft.add(R.id.realtabcontent, newTab.fragment, newTab.tag);
}
else
{
ft.attach(newTab.fragment);
}
}
mLastTab = newTab;
ft.commit();
this.getSupportFragmentManager().executePendingTransactions();
}
}