用FragmentTabHost管理Fragment,实现页面切换
现在大多数的应用的主页面都有点类似新浪微博的主页面,下方是一个导航栏,点击导航栏会进行页面的切换。从技术实现上来说,这并不复杂,可以有很多方法来实现,比如用radiogroup和fragment配合就可以。可是这样我们并不是我们想要的,因为这样写需要我们自己写不少逻辑去控制。俗话说不会偷懒的程序员不是好程序员,所以我们希望系统给我们提供一个可以对Fragment管理的类,我们不用关心太多的逻辑,只需要做好相应Fragment的显示,那样是不是很爽。值得高兴的是系统真的提供了这样一个类:FragmentTabHost。可是它存在一个缺陷,到后面再说,我们先简单看一下它的用法。 它的用法和别的控件一样需要我们先在布局文件中声明,如下: <?xml version="1.0" encoding="utf-8"?> <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"> <!--fragment容器--> <FrameLayout android:id="@+id/container_fragment" android:layout_width="fill_parent" android:layout_height="0dip" android:layout_weight="1" /> <!--分割线--> <View android:layout_width="match_parent" android:layout_height="1px" android:background="#dcdcdc" /> <!--下方导航栏--> <android.support.v4.app.FragmentTabHost android:id="@android:id/tabhost" android:layout_width="fill_parent" android:layout_height="wrap_content"> <FrameLayout android:id="@+id/container_tab" android:layout_width="0dp" android:layout_height="0dp" android:layout_weight="0" /> </android.support.v4.app.FragmentTabHost> </LinearLayout> 来自CODE的代码片 activity_main.xml 接下来我们就需要创建导航栏单个item的通用布局,如下: <?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent" android:layout_height="match_parent" android:gravity="center" android:orientation="vertical"> <ImageView android:id="@+id/tab_icon" android:layout_width="wrap_content" android:layout_height="wrap_content" android:focusable="false" android:padding="3dp"/> <TextView android:id="@+id/tab_text" android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="" android:textColor="@drawable/selector_text" android:textSize="15sp"/> </LinearLayout> 来自CODE的代码片 tab_item_view.xml 这里只是简单的演示一下用法,Fragment布局里面就一个TextView用于在切换的时候区分,这里就不贴代码了。 接下来我们在activity里面进行设置就可以了,代码如下: package com.demo.zhangs.demo_fragmenttabhost; import android.os.Bundle; import android.support.v4.app.FragmentActivity; import android.support.v4.app.FragmentTabHost; import android.view.LayoutInflater; import android.view.View; import android.widget.ImageView; import android.widget.TabHost; import android.widget.TextView; /** * Created by Admin on 2016/5/18. */ public class MainActivity extends FragmentActivity { private static final String TAG = "MainActivity"; //定义FragmentTabHost对象 private FragmentTabHost mTabHost; //定义一个布局 private LayoutInflater layoutInflater; //定义数组来存放Fragment界面 private Class fragmentArray[] = {Fragment_home.class, Fragment_quotation.class, Fragment_me.class}; //定义数组来存放按钮图片 private int mImageViewArray[] = {R.drawable.selector_home, R.drawable.selector_quotation, R.drawable.selector_me}; //Tab选项卡的文字 private String mTextviewArray[] = {"首页", "报价单", "我的"}; @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); initView(); } /** * 初始化组件 */ private void initView() { //实例化布局对象 layoutInflater = LayoutInflater.from(this); //实例化TabHost对象,得到TabHost mTabHost = (FragmentTabHost) findViewById(android.R.id.tabhost); mTabHost.setup(this, getSupportFragmentManager(), R.id.container_fragment); //得到fragment的个数 int count = fragmentArray.length; for (int i = 0; i < count; i++) { //为每一个Tab按钮设置图标、文字和内容 TabHost.TabSpec tabSpec = mTabHost.newTabSpec(mTextviewArray[i]).setIndicator(getTabItemView(i)); //将Tab按钮添加进Tab选项卡中 mTabHost.addTab(tabSpec, fragmentArray[i], null); //可以根据自己的需求设置Tab按钮的背景 // mTabHost.getTabWidget().getChildAt(i).setBackgroundResource(R.drawable.selector_tab_background); } } /** * 给Tab按钮设置图标和文字 */ private View getTabItemView(int index) { View view = layoutInflater.inflate(R.layout.tab_item_view, null); ImageView imageView = (ImageView) view.findViewById(R.id.tab_icon); imageView.setImageResource(mImageViewArray[index]); TextView textView = (TextView) view.findViewById(R.id.tab_text); textView.setText(mTextviewArray[index]); return view; } } 来自CODE的代码片 MainActivity.java 简单看一下效果: ok~效果出来了 上面说过它存在一个缺陷,缺陷就是每次FragmentTabHost切换fragment时会重新调用onCreateView()重新绘制UI。假如我们在onCreateView()中有网络操作,在切换的时候也会重复进行,这样当然不是我们希望的。当然也有解决方法,我们可以在onCreateView()方法里面做一些处理: private View rootView;// 缓存Fragment view @Override public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) { Log.i(TAG, "onCreateView"); if (rootView == null) { rootView = inflater.inflate(R.layout.fragment_home, null); //假如有网络操作建议放在这里面,避免重复加载 } // 缓存的rootView需要判断是否已经被加过parent,如果有parent需要从parent删除,要不然会发生这个rootview已经有parent的错误。 ViewGroup parent = (ViewGroup) rootView.getParent(); if (parent != null) { parent.removeView(rootView); } return rootView; } 到这也算是比较圆满了,可是大家想过没有,假如它内部能够通过hide和show来管理fragment多好,这样我们就不用做以上处理,而且在效率上也会高了很多。下面我就贴一个重写了的FragmentTabHost它的内部就是通过hide和show来隐藏和显示Fragment的,而且它的用法和系统的完全一样。大家可以导入到自己的项目中,直接使用。 /* * Copyright (C) 2012 The Android Open Source Project * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package com.demo.zhangs.demo_fragmenttabhost; import android.content.Context; import android.content.res.TypedArray; import android.os.Bundle; import android.os.Parcel; import android.os.Parcelable; import android.support.v4.app.Fragment; import android.support.v4.app.FragmentManager; import android.support.v4.app.FragmentTransaction; import android.util.AttributeSet; import android.view.View; import android.view.ViewGroup; import android.widget.FrameLayout; import android.widget.LinearLayout; import android.widget.TabHost; import android.widget.TabWidget; import java.util.ArrayList; /** * Special TabHost that allows the use of {@link Fragment} objects for its tab * content. When placing this in a view hierarchy, after inflating the hierarchy * you must call {@link #setup(Context, FragmentManager, int)} to complete the * initialization of the tab host. * * <p> * Here is a simple example of using a FragmentTabHost in an Activity: * * {@sample * development/samples/Support4Demos/src/com/example/android/supportv4/app/ * FragmentTabs.java complete} * * <p> * This can also be used inside of a fragment through fragment nesting: * * {@sample * development/samples/Support4Demos/src/com/example/android/supportv4/app/ * FragmentTabsFragmentSupport.java complete} */ public class FragmentTabHost extends TabHost implements TabHost.OnTabChangeListener { private final ArrayList<TabInfo> mTabs = new ArrayList<TabInfo>(); private FrameLayout mRealTabContent; private Context mContext; private FragmentManager mFragmentManager; private int mContainerId; private OnTabChangeListener mOnTabChangeListener; private TabInfo mLastTab; private boolean mAttached; static final class TabInfo { private final String tag; private final Class<?> clss; private final Bundle args; private Fragment fragment; TabInfo(String _tag, Class<?> _class, Bundle _args) { tag = _tag; clss = _class; args = _args; } } static class DummyTabFactory implements TabContentFactory { private final Context mContext; public DummyTabFactory(Context context) { mContext = context; } @Override public View createTabContent(String tag) { View v = new View(mContext); v.setMinimumWidth(0); v.setMinimumHeight(0); return v; } } static class SavedState extends BaseSavedState { String curTab; SavedState(Parcelable superState) { super(superState); } private SavedState(Parcel in) { super(in); curTab = in.readString(); } @Override public void writeToParcel(Parcel out, int flags) { super.writeToParcel(out, flags); out.writeString(curTab); } @Override public String toString() { return "FragmentTabHost.SavedState{" + Integer.toHexString(System.identityHashCode(this)) + " curTab=" + curTab + "}"; } public static final Creator<SavedState> CREATOR = new Creator<SavedState>() { public SavedState createFromParcel(Parcel in) { return new SavedState(in); } public SavedState[] newArray(int size) { return new SavedState[size]; } }; } public FragmentTabHost(Context context) { // Note that we call through to the version that takes an AttributeSet, // because the simple Context construct can result in a broken object! super(context, null); initFragmentTabHost(context, null); } public FragmentTabHost(Context context, AttributeSet attrs) { super(context, attrs); initFragmentTabHost(context, attrs); } private void initFragmentTabHost(Context context, AttributeSet attrs) { TypedArray a = context.obtainStyledAttributes(attrs, new int[] { android.R.attr.inflatedId }, 0, 0); mContainerId = a.getResourceId(0, 0); a.recycle(); super.setOnTabChangedListener(this); } private void ensureHierarchy(Context context) { // If owner hasn't made its own view hierarchy, then as a convenience // we will construct a standard one here. if (findViewById(android.R.id.tabs) == null) { LinearLayout ll = new LinearLayout(context); ll.setOrientation(LinearLayout.VERTICAL); addView(ll, new LayoutParams( ViewGroup.LayoutParams.MATCH_PARENT, ViewGroup.LayoutParams.MATCH_PARENT)); TabWidget tw = new TabWidget(context); tw.setId(android.R.id.tabs); tw.setOrientation(TabWidget.HORIZONTAL); ll.addView(tw, new LinearLayout.LayoutParams( ViewGroup.LayoutParams.MATCH_PARENT, ViewGroup.LayoutParams.WRAP_CONTENT, 0)); FrameLayout fl = new FrameLayout(context); fl.setId(android.R.id.tabcontent); ll.addView(fl, new LinearLayout.LayoutParams(0, 0, 0)); mRealTabContent = fl = new FrameLayout(context); mRealTabContent.setId(mContainerId); ll.addView(fl, new LinearLayout.LayoutParams( LinearLayout.LayoutParams.MATCH_PARENT, 0, 1)); } } /** * @deprecated Don't call the original TabHost setup, you must instead call * {@link #setup(Context, FragmentManager)} or * {@link #setup(Context, FragmentManager, int)}. */ @Override @Deprecated public void setup() { throw new IllegalStateException( "Must call setup() that takes a Context and FragmentManager"); } public void setup(Context context, FragmentManager manager) { ensureHierarchy(context); // Ensure views required by super.setup() super.setup(); mContext = context; mFragmentManager = manager; ensureContent(); } public void setup(Context context, FragmentManager manager, int containerId) { ensureHierarchy(context); // Ensure views required by super.setup() super.setup(); mContext = context; mFragmentManager = manager; mContainerId = containerId; ensureContent(); mRealTabContent.setId(containerId); // We must have an ID to be able to save/restore our state. If // the owner hasn't set one at this point, we will set it ourself. if (getId() == View.NO_ID) { setId(android.R.id.tabhost); } } private void ensureContent() { if (mRealTabContent == null) { mRealTabContent = (FrameLayout) findViewById(mContainerId); if (mRealTabContent == null) { throw new IllegalStateException( "No tab content FrameLayout found for id " + mContainerId); } } } @Override public void setOnTabChangedListener(OnTabChangeListener l) { mOnTabChangeListener = l; } public void addTab(TabSpec tabSpec, Class<?> clss, Bundle args) { tabSpec.setContent(new DummyTabFactory(mContext)); String tag = tabSpec.getTag(); TabInfo info = new TabInfo(tag, clss, args); if (mAttached) { // If we are already attached to the window, then check to make // sure this tab's fragment is inactive if it exists. This shouldn't // normally happen. info.fragment = mFragmentManager.findFragmentByTag(tag); if (info.fragment != null && !info.fragment.isDetached()) { FragmentTransaction ft = mFragmentManager.beginTransaction(); // ft.detach(info.fragment); ft.hide(info.fragment); ft.commit(); } } mTabs.add(info); addTab(tabSpec); } @Override protected void onAttachedToWindow() { super.onAttachedToWindow(); String currentTab = getCurrentTabTag(); // Go through all tabs and make sure their fragments match // the correct state. FragmentTransaction ft = null; for (int i = 0; i < mTabs.size(); i++) { TabInfo tab = mTabs.get(i); tab.fragment = mFragmentManager.findFragmentByTag(tab.tag); // if (tab.fragment != null && !tab.fragment.isDetached()) { if (tab.fragment != null) { if (tab.tag.equals(currentTab)) { // The fragment for this tab is already there and // active, and it is what we really want to have // as the current tab. Nothing to do. mLastTab = tab; } else { // This fragment was restored in the active state, // but is not the current tab. Deactivate it. if (ft == null) { ft = mFragmentManager.beginTransaction(); } // ft.detach(tab.fragment); ft.hide(tab.fragment); } } } // We are now ready to go. Make sure we are switched to the // correct tab. mAttached = true; ft = doTabChanged(currentTab, ft); if (ft != null) { ft.commit(); mFragmentManager.executePendingTransactions(); } } @Override protected void onDetachedFromWindow() { super.onDetachedFromWindow(); mAttached = false; } @Override protected Parcelable onSaveInstanceState() { Parcelable superState = super.onSaveInstanceState(); SavedState ss = new SavedState(superState); ss.curTab = getCurrentTabTag(); return ss; } @Override protected void onRestoreInstanceState(Parcelable state) { SavedState ss = (SavedState) state; super.onRestoreInstanceState(ss.getSuperState()); setCurrentTabByTag(ss.curTab); } @Override public void onTabChanged(String tabId) { if (mAttached) { FragmentTransaction ft = doTabChanged(tabId, null); if (ft != null) { ft.commit(); } } if (mOnTabChangeListener != null) { mOnTabChangeListener.onTabChanged(tabId); } } private FragmentTransaction doTabChanged(String tabId, FragmentTransaction ft) { TabInfo newTab = null; for (int i = 0; i < mTabs.size(); i++) { TabInfo tab = mTabs.get(i); if (tab.tag.equals(tabId)) { newTab = tab; } } if (newTab == null) { throw new IllegalStateException("No tab known for tag " + tabId); } if (mLastTab != newTab) { if (ft == null) { ft = mFragmentManager.beginTransaction(); } if (mLastTab != null) { if (mLastTab.fragment != null) { // ft.detach(mLastTab.fragment); ft.hide(mLastTab.fragment); } } if (newTab != null) { if (newTab.fragment == null) { newTab.fragment = Fragment.instantiate(mContext, newTab.clss.getName(), newTab.args); ft.add(mContainerId, newTab.fragment, newTab.tag); } else { // ft.attach(newTab.fragment); ft.show(newTab.fragment); } } mLastTab = newTab; } return ft; } }
现在大多数的应用的主页面都有点类似新浪微博的主页面,下方是一个导航栏,点击导航栏会进行页面的切换。从技术实现上来说,这并不复杂,可以有很多方法来实现,比如用radiogroup和fragment配合就可以。可是这样我们并不是我们想要的,因为这样写需要我们自己写不少逻辑去控制。俗话说不会偷懒的程序员不是好程序员,所以我们希望系统给我们提供一个可以对Fragment管理的类,我们不用关心太多的逻辑,只需要做好相应Fragment的显示,那样是不是很爽。值得高兴的是系统真的提供了这样一个类:FragmentTabHost。可是它存在一个缺陷,到后面再说,我们先简单看一下它的用法。
它的用法和别的控件一样需要我们先在布局文件中声明,如下:
来自CODE的代码片
activity_main.xml
接下来我们就需要创建导航栏单个item的通用布局,如下:
这里只是简单的演示一下用法,Fragment布局里面就一个TextView用于在切换的时候区分,这里就不贴代码了。
接下来我们在activity里面进行设置就可以了,代码如下:
ok~效果出来了 上面说过它存在一个缺陷,缺陷就是每次FragmentTabHost切换fragment时会重新调用onCreateView()重新绘制UI。假如我们在onCreateView()中有网络操作,在切换的时候也会重复进行,这样当然不是我们希望的。当然也有解决方法,我们可以在onCreateView()方法里面做一些处理:
private View rootView;// 缓存Fragment view @Override public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) { Log.i(TAG, "onCreateView"); if (rootView == null) { rootView = inflater.inflate(R.layout.fragment_home, null); //假如有网络操作建议放在这里面,避免重复加载 } // 缓存的rootView需要判断是否已经被加过parent,如果有parent需要从parent删除,要不然会发生这个rootview已经有parent的错误。 ViewGroup parent = (ViewGroup) rootView.getParent(); if (parent != null) { parent.removeView(rootView); } return rootView; }到这也算是比较圆满了,可是大家想过没有,假如它内部能够通过hide和show来管理fragment多好,这样我们就不用做以上处理,而且在效率上也会高了很多。下面我就贴一个重写了的FragmentTabHost它的内部就是通过hide和show来隐藏和显示Fragment的,而且它的用法和系统的完全一样。大家可以导入到自己的项目中,直接使用。