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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。

我的项目配置了 supportev4 库，但无法正常工作。

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;
}
*/
}

更新

我的日志猫

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
4

1 回答 1

1

在您的initializeTabHost(Bundle)方法中，您将使用 Class 创建一个新的 TabInfo 对象，MainActivity然后Fragment在您的方法中使用相同的类实例化一个onTabChanged(String)。您需要MainActivity扩展Fragment，然后实例化 newTab.clss 并将其转换为片段。

编辑：添加了类类型的验证

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();
    }
}
于 2013-09-05T02:56:09.097 回答