Android组件：Fragment切换后保存状态（精选2篇）由网友“天天幽雅”投稿提供，下面是小编收集整理的Android组件：Fragment切换后保存状态，供大家参考借鉴，欢迎大家分享。
篇1：Android组件：Fragment切换后保存状态
之前写的第一篇Fragment实例，和大多数人一开始学的一样，都是通过FragmentTransaction的replace方法来实现，replace方法相当于先移除remove原来所有已存在的fragments，然后添加add()当前这个fragment，这就导致了一个问题，我们切换一次，然后再切换回来，相当于重新加载了这个fragment，原来的状态不复存在，这显然与我们的日常使用不符。想要保存切换后的状态，思路还是很简单的，我们先添加了若干fragments，切换后将所有fragments都隐藏hide()，并显示show()切换后的fragment即可。
实例：山寨微信
由于代码较长，这里只讲核心的部分，有兴趣的可以下载源码来看一下
public class MainActivity extends ActionBarActivity implements OnClickListener { private View weixinLayout, tongxunluLayout, faxianLayout, woLayout; private TextView weixinTv, tongxunluTv, faxianTv, woTv; private ImageView weixinIv, tongxunluIv, faxianIv, woIv; private Fragment1 fragment1; private Fragment2 fragment2; private Fragment3 fragment3; private Fragment4 fragment4; private FragmentManager fm; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); // 初始化 initViews(); fm = getFragmentManager(); // 初识状态是显示微信 weixinIv.setBackgroundResource(R.drawable.weixin2); weixinTv.setTextColor(getResources().getColor(R.color.green)); showFragment(1); } void initViews() { // 注册各IamgeView weixinIv = (ImageView) findViewById(R.id.weixin_iv); tongxunluIv = (ImageView) findViewById(R.id.tongxunlu_iv); faxianIv = (ImageView) findViewById(R.id.faxian_iv); woIv = (ImageView) findViewById(R.id.wo_iv); // 注册各TextView weixinTv = (TextView) findViewById(R.id.weixin_tv); tongxunluTv = (TextView) findViewById(R.id.tongxunlu_tv); faxianTv = (TextView) findViewById(R.id.faxian_tv); woTv = (TextView) findViewById(R.id.wo_tv); // 注册各Layout weixinLayout = (View) findViewById(R.id.weixin_layout); tongxunluLayout = (View) findViewById(R.id.tongxunlu_layout); faxianLayout = (View) findViewById(R.id.faxian_layout); woLayout = (View) findViewById(R.id.wo_layout); // 各Layout注册 weixinLayout.setOnClickListener(this); tongxunluLayout.setOnClickListener(this); faxianLayout.setOnClickListener(this); woLayout.setOnClickListener(this); } @Override public void onClick(View arg0) { // TODO Auto-generated method stub // 当点击某个layout时，先清除状态，这里的状态指的是布局里面的图片和文字 clearState(); switch (arg0.getId()) { case R.id.weixin_layout: // 如果点的是微信，将微信布局的图片和文字的颜色变为绿色 weixinIv.setBackgroundResource(R.drawable.weixin2); weixinTv.setTextColor(getResources().getColor(R.color.green)); // 显示微信的fragment showFragment(1); break; case R.id.tongxunlu_layout: tongxunluIv.setBackgroundResource(R.drawable.tongxunlu2); tongxunluTv.setTextColor(getResources().getColor(R.color.green)); showFragment(2); break; case R.id.faxian_layout: faxianIv.setBackgroundResource(R.drawable.faxian2); faxianTv.setTextColor(getResources().getColor(R.color.green)); showFragment(3); break; case R.id.wo_layout: woIv.setBackgroundResource(R.drawable.wo2); woTv.setTextColor(getResources().getColor(R.color.green)); showFragment(4); break; } } public void clearState() { // 未选中时的图片 weixinIv.setBackgroundResource(R.drawable.weixin1); tongxunluIv.setBackgroundResource(R.drawable.tongxunlu1); faxianIv.setBackgroundResource(R.drawable.faxian1); woIv.setBackgroundResource(R.drawable.wo1); // 未选中时字体颜色 weixinTv.setTextColor(getResources().getColor(R.color.black)); tongxunluTv.setTextColor(getResources().getColor(R.color.black)); faxianTv.setTextColor(getResources().getColor(R.color.black)); woTv.setTextColor(getResources().getColor(R.color.black)); } public void showFragment(int index) { FragmentTransaction ft = fm.beginTransaction(); // 想要显示一个fragment,先隐藏所有fragment，防止重叠 hideFragments(ft); switch (index) { case 1: // 如果fragment1已经存在则将其显示出来 if (fragment1 != null) ft.show(fragment1); // 否则是第一次切换则添加fragment1，注意添加后是会显示出来的，replace方法也是先remove后add else { fragment1 = new Fragment1(); ft.add(R.id.content, fragment1); } break; case 2: if (fragment2 != null) ft.show(fragment2); else { fragment2 = new Fragment2(); ft.add(R.id.content, fragment2); } break; case 3: if (fragment3 != null) ft.show(fragment3); else { fragment3 = new Fragment3(); ft.add(R.id.content, fragment3); } break; case 4: if (fragment4 != null) ft.show(fragment4); else { fragment4 = new Fragment4(); ft.add(R.id.content, fragment4); } break; } ft.commit(); } // 当fragment已被实例化，就隐藏起来 public void hideFragments(FragmentTransaction ft) { if (fragment1 != null) ft.hide(fragment1); if (fragment2 != null) ft.hide(fragment2); if (fragment3 != null) ft.hide(fragment3); if (fragment4 != null) ft.hide(fragment4); }}
当我们一开始把微信fragment的ListView下拉到如上图时，切换到通讯录fragment，然后再切换回去微信fragment，此时微信的ListView还是原来的状态，这是因为并非重新加载微信fragment，而是将其先hide起来，切换回来后再show出来，
引用上篇文章的fragment生命周期图：
如果是repalce方法，我们切换至当前fragment则进行红线以上的生命周期，切换到其他fragment后进行红线以下的生命周期。但是，如果我们使用hide()和show()的方法，切换至当前fragment依然进行红线以上的生命周期，切换到其他fragment后并没有进行其他生命周期，只是简单地隐藏了起来。这样应该很明了了吧。
源码：
download.csdn.net/detail/leelit/8179147
篇2：Android重写FragmentTabHost来实现状态保存
最近要做一个类似QQ底部有气泡的功能，试了几个方案不太好，我想很多开发者使用TabHost都会知道它不保存状态，每次都要重新加载布局，为了保存状态，使用RadioGroup来实现，状态是可以保存了，问题是无法实现气泡功能，不能自定义布局，因为RadioGroup里面只能包含RadioButton，不然状态切换不起用作，这个可以查看RadioGroup源码，为了既能保存状态又能实现气泡功能，所以只能自己修改控件了或者自己写一个类似的切换功能，查看了FragmentTabHost的源码，可以知道FragmentTabHost不保存状态是因为切换fragment的时候是使用detach和attach来Fragment的隐藏和显示的，这样的话每次切换肯定要重新加载布局，处理使用detach和attach，我们还可以使用show和hide来实现显示和隐藏，这样可以保存状态，方案出来了就是修改FragmentTabHost源码将切换Fragment的方式detach和attach改为hide和show，
下面就是修改后的FragmentTabHost的源码：
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/*
* 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
*
* 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.jwzhangjie.com;
import java.util.ArrayList;
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;
/**
* 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.
*
*
* 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}
*
*
* 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
private FrameLayout mRealTabContent;
private Context mContext;
private FragmentManager mFragmentManager;
private int mContainerId;
private TabHost.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 TabHost.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 Parcelable.Creator
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 FrameLayout.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(TabHost.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;
}
}
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