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这是我的应用程序的范围：

我正在尝试使用 ViewPager 和 Fragment 编写应用程序。应用程序的布局有 2 个选项卡（主页/配置）。这些选项卡之一的片段可以更改为另一个。例如：* FragmentHome（在 TabHome 中）被 FragmentGraphics 替换。如果用户按下按钮返回，FragmentHome 将再次显示。

问题（1）：应用程序在打开之前崩溃并关闭。我不知道会发生什么。问题（2）：如何用另一个视图寻呼机替换片段？（FragmentHome 中的 button1ClickListener）？

希望得到帮助！

代码：

ActivityMain.java

import java.util.List;
import java.util.Vector;

import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentActivity;
import android.support.v4.view.ViewPager;
import android.widget.TabHost;
import android.widget.TabHost.TabSpec;

public class ActivityMain extends FragmentActivity {

    private TabHost mTabHost;
    private PagerAdapter mPagerAdapter;
    private ViewPager mViewPager;

    List<Fragment> fragments = new Vector<Fragment>();

    @Override
    protected void onSaveInstanceState(Bundle outState) {
        super.onSaveInstanceState(outState);
    }

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        setContentView(R.layout.main);

        this.setLayout(savedInstanceState);

    }

    @Override
    public void onBackPressed() {
      if(!mPagerAdapter.back(getSupportFragmentManager())) {
        super.onBackPressed();
      }
    }    

    public void setLayout(Bundle args){

        this.mViewPager = (ViewPager)findViewById(R.id.viewpager);

        this.mTabHost = (TabHost)findViewById(android.R.id.tabhost);    

        //HomeTab
        TabSpec tabSpecHome = mTabHost.newTabSpec(getResources().getString(R.string.tab_home_name));
        tabSpecHome.setIndicator(getResources().getString(R.string.tab_home_label));

        //ConfigTab
        TabSpec tabSpecConfig = mTabHost.newTabSpec(getResources().getString(R.string.tab_config_name));
        tabSpecConfig.setIndicator(getResources().getString(R.string.tab_config_label));

        this.mPagerAdapter  = new PagerAdapter(this, this.mTabHost,this.mViewPager);

        //HomeTab
        this.mPagerAdapter.addTab(tabSpecHome, FragmentHome.class, args);
        this.mPagerAdapter.addFragment(getSupportFragmentManager(), getResources().getString(R.string.tab_home_name), FragmentHome.class, null);

        //ConfigTab
        this.mPagerAdapter.addTab(tabSpecConfig, FragmentConfig.class, args);
        this.mPagerAdapter.addFragment(getSupportFragmentManager(), getResources().getString(R.string.tab_config_name), FragmentConfig.class, null);

    }
}

PagerAdapter.java

import java.util.ArrayList;
import java.util.HashMap;
import java.util.Stack;

import android.content.Context;
import android.os.Bundle;
import android.support.v4.app.FragmentActivity;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentPagerAdapter;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentTransaction;
import android.support.v4.view.ViewPager;
import android.view.ViewGroup;
import android.widget.TabHost;
import android.widget.TabHost.TabSpec;
import android.widget.TabWidget;

public class PagerAdapter extends FragmentPagerAdapter {

    private final Context mContext;
    private final TabHost mTabHost;
    private final ViewPager mViewPager;

    private ArrayList<String> mTabTags = new ArrayList<String>();
    private HashMap<String, Stack<TabInfo>> mTabStackMap = new HashMap<String, Stack<TabInfo>>();

    public interface SaveStateBundle{
        public Bundle onRemoveFragment(Bundle outState);
    }

    public PagerAdapter(FragmentActivity activity, TabHost tabHost, ViewPager pager){

        super(activity.getSupportFragmentManager());
        this.mContext = activity;

        this.mTabHost = tabHost;
        this.mTabHost.setOnTabChangedListener(tabChangeListener);

        this.mViewPager = pager;
        this.mViewPager.setAdapter(this);
        this.mViewPager.setOnPageChangeListener(viewPagerChangeListener);
    }

    @Override
    public Fragment getItem(int position) {
        Stack<TabInfo> tabStack = mTabStackMap.get(mTabTags.get(position));
        TabInfo info = tabStack.peek();
        return Fragment.instantiate(mContext, info.getClass().getName(), info.getArgs());
    }

    @Override
    public int getItemPosition(Object object) {
        ArrayList<Class<?>> positionNoneHack = new ArrayList<Class<?>>();

        for(Stack<TabInfo> tabStack: mTabStackMap.values()){
            positionNoneHack.add(tabStack.peek().getClass());
        }

        if(positionNoneHack.contains(object.getClass())){
            return POSITION_UNCHANGED;
        }

        return POSITION_NONE;
    }

    public void addTab(TabSpec tabSpec, Class<?> clss, Bundle args){

        try{

            this.mTabHost.setup();

            Stack<TabInfo> tabStack = new Stack<TabInfo>();

            tabSpec.setContent(new TabContent(this.mContext));
            this.mTabHost.addTab(tabSpec);
            String tag = tabSpec.getTag();
            TabInfo info = new TabInfo(tag, clss, args);

            this.mTabTags.add(tag);
            tabStack.add(info);
            this.mTabStackMap.put(tag, tabStack);
            notifyDataSetChanged();
        }catch(Exception ex){
            ex.printStackTrace();
        }
    }    

    public void addFragment(FragmentManager fm, String _tag, Class<?> _class, Bundle _args){

        try{

            TabInfo info = new TabInfo(_tag, _class, _args);
            Stack<TabInfo> tabStack = mTabStackMap.get(_tag);

            Fragment frag = fm.findFragmentByTag("android:switcher:" + mViewPager.getId() + ":" + mTabTags.indexOf(_tag));
            if(frag instanceof SaveStateBundle){
                Bundle b = new Bundle();
                ((SaveStateBundle) frag).onRemoveFragment(b);
                tabStack.peek().setArgs(b);
            }
            tabStack.add(info);

            FragmentTransaction ft = fm.beginTransaction();

            ft.remove(frag);

            ft.addToBackStack(null);

            ft.commit();

            notifyDataSetChanged();
        }catch(Exception ex){
            ex.printStackTrace();
        }
    }

    public boolean popFragment(FragmentManager fm, String _tag){
        Stack<TabInfo> tabStack = mTabStackMap.get(_tag);   
        if(tabStack.size()>1){
            tabStack.pop();
            Fragment frag = fm.findFragmentByTag("android:switcher:" + mViewPager.getId() + ":" + mTabTags.indexOf(_tag));

            FragmentTransaction ft = fm.beginTransaction();

            ft.remove(frag);

            ft.addToBackStack(null);

            ft.commit();

            notifyDataSetChanged();

            return true;
        }
        return false;
    }

    public boolean back(FragmentManager fm) {
        int position = mViewPager.getCurrentItem();
        return popFragment(fm, mTabTags.get(position));
    }

    @Override
    public int getCount() {
        return mTabStackMap.size();
    }

    @Override
    public void notifyDataSetChanged(){
        super.notifyDataSetChanged();
    }

    private final ViewPager.OnPageChangeListener viewPagerChangeListener = new  ViewPager.OnPageChangeListener(){

        @Override
        public void onPageScrollStateChanged(int arg0) {
            // TODO Auto-generated method stub
        }

        @Override
        public void onPageScrolled(int arg0, float arg1, int arg2) {
            // TODO Auto-generated method stub
        }

        @Override
        public void onPageSelected(int position) {
            // TODO Auto-generated method stub
            TabWidget widget = mTabHost.getTabWidget();
            int oldFocusability = widget.getDescendantFocusability();
            widget.setDescendantFocusability(ViewGroup.FOCUS_BLOCK_DESCENDANTS);
            mTabHost.setCurrentTab(position);
            widget.setDescendantFocusability(oldFocusability);
        }
    };

    private final TabHost.OnTabChangeListener tabChangeListener = new TabHost.OnTabChangeListener(){

        @Override
        public void onTabChanged(String tabId) {
            int pos = mTabHost.getCurrentTab();
            mViewPager.setCurrentItem(pos);         
        }

    };  
}

TabContent.java

import android.content.Context;
import android.view.View;
import android.widget.TabHost.TabContentFactory;

public class TabContent implements TabContentFactory{

    private final Context mContext;

    public TabContent(Context context){
        mContext = context;
    }

    @Override
    public View createTabContent(String tag) {
        View v = new View(mContext);
        v.setMinimumWidth(0);
        v.setMinimumHeight(0);        
        return v;
    }
}

TabInfo.java

import android.os.Bundle;
import android.support.v4.app.Fragment;

public class TabInfo {

    private String tag;
    private Class<?> clss;
    private Bundle args;
    private Fragment fragment;

    public TabInfo(String tag, Class<?> clazz, Bundle args) {
        this.tag = tag;
        this.clss = clazz;
        this.args = args;
    }

    public void setTag(String tag){
        this.tag = tag;
    }

    public String getTag(){
        return this.tag;
    }

    public void setClazz(Class<?> clzz){
        this.clss = clzz;
    }

    public Class<?> getClazz(){
        return this.clss;
    }

    public void setArgs(Bundle args){
        this.args = args;
    }

    public Bundle getArgs(){
        return this.args;
    }

    public Fragment getFragment(){
        return this.fragment;
    }

}

片段主页.java

import android.support.v4.app.Fragment;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;

public class FragmentHome extends Fragment{

    Button button1;
    View view;  

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

        if(container == null){
            return null;
        }

        this.view = inflater.inflate(R.layout.home, container, false);

        this.setItens();

        return this.view;
    }

    private void setItens(){

        button1 = (Button)this.view.findViewById(R.id.button1);
        button1.setOnClickListener(button1OnClickListener);
    }

    private final View.OnClickListener button1OnClickListener = new View.OnClickListener(){

        public void onClick(View v) {
            showFragmentGraphics();
        }
    };

    public void showFragmentGraphics(){
        //the code for replace fragment home
    }

}

显现

<manifest
    xmlns:android="http://schemas.android.com/apk/res/android"
    package="br.com.my.app"
    android:versionCode="1"
    android:versionName="1.0.0"
    android:installLocation="internalOnly">

    <uses-sdk
        android:minSdkVersion="7"
        android:targetSdkVersion="17" />

    <uses-permission android:name="android.permission.INTERNET" />

    <application
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >

        <activity
            android:name=".ActivityMain"
            android:screenOrientation="portrait"
            android:configChanges="keyboardHidden|orientation">
            <intent-filter android:label="@string/app_name">
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>        

    </application>

</manifest>

现在，错误日志

04-30 18:56:19.591: E/AndroidRuntime(1275): FATAL EXCEPTION: main
04-30 18:56:19.591: E/AndroidRuntime(1275): java.lang.RuntimeException: Unable to start activity ComponentInfo{br.com.my.app/br.com.my.app.ActivityMain}: java.lang.NullPointerException
04-30 18:56:19.591: E/AndroidRuntime(1275):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1647)
04-30 18:56:19.591: E/AndroidRuntime(1275):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1663)
04-30 18:56:19.591: E/AndroidRuntime(1275):     at android.app.ActivityThread.access$1500(ActivityThread.java:117)
04-30 18:56:19.591: E/AndroidRuntime(1275):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:931)
04-30 18:56:19.591: E/AndroidRuntime(1275):     at android.os.Handler.dispatchMessage(Handler.java:99)
04-30 18:56:19.591: E/AndroidRuntime(1275):     at android.os.Looper.loop(Looper.java:123)
04-30 18:56:19.591: E/AndroidRuntime(1275):     at android.app.ActivityThread.main(ActivityThread.java:3683)
04-30 18:56:19.591: E/AndroidRuntime(1275):     at java.lang.reflect.Method.invokeNative(Native Method)
04-30 18:56:19.591: E/AndroidRuntime(1275):     at java.lang.reflect.Method.invoke(Method.java:507)
04-30 18:56:19.591: E/AndroidRuntime(1275):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
04-30 18:56:19.591: E/AndroidRuntime(1275):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
04-30 18:56:19.591: E/AndroidRuntime(1275):     at dalvik.system.NativeStart.main(Native Method)
04-30 18:56:19.591: E/AndroidRuntime(1275): Caused by: java.lang.NullPointerException
04-30 18:56:19.591: E/AndroidRuntime(1275):     at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:651)
04-30 18:56:19.591: E/AndroidRuntime(1275):     at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1444)
04-30 18:56:19.591: E/AndroidRuntime(1275):     at android.support.v4.app.FragmentActivity.onStart(FragmentActivity.java:551)
04-30 18:56:19.591: E/AndroidRuntime(1275):     at android.app.Instrumentation.callActivityOnStart(Instrumentation.java:1129)
04-30 18:56:19.591: E/AndroidRuntime(1275):     at android.app.Activity.performStart(Activity.java:3791)
04-30 18:56:19.591: E/AndroidRuntime(1275):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1620)
04-30 18:56:19.591: E/AndroidRuntime(1275):     ... 11 more
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1 回答 1

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对于第一个问题，您可以尝试从

this.mTabHost = (TabHost)findViewById(android.R.id.tabhost);

至

this.mTabHost = (TabHost)findViewById(R.id.tabhost);

对于第二个问题，您可以检查ViewPager 中的 Replace Fragment。

老实说，您的代码和设计非常混乱。您应该花一些时间阅读有关 ViewPager 和 Tab 的信息。

于 2013-04-30T20:27:50.773 回答