Problem background:
The company's App home page structure uses the FragmentTabHost + Fragment structure. In order to solve the problem that Fragment does not reload every time the tab is switched, the FragmentTabHost class is rewritten. The core code of the rewritten class is as follows:
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);
}
// 防止画面被回收后Fragment白屏
if (isRestored) {
if (mTabs != null && mTabs.size() > 0) {
for (int i=0; i<mTabs.size(); i++) {
TabInfo tab = mTabs.get(i);
if (!tab.tag.equals(mLastTab.tag)) {
tab.fragment = null;
}
}
}
isRestored = false;
}
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;
}The essence is to replace ft.detach and ft.attach in the original FragmentTabHost with ft.hide and ft.show.
This does achieve the goal of not having to re-go the Fragment life cycle when switching tabs. But related side effects also appeared: after the host Activity was recycled, the App was reopened, and after the host Activity was re-created, when the tab was switched, the Fragment white screen would appear.
The reason for the problem is that when the ft.show method is called, the onCreateView method of Fragment will not be re-goed. After the overall Activity is recycled, the screen elements in the corresponding Fragment are also recycled. If you want to rebuild the screen elements, you must call the onCreateView method of the corresponding Fragment.
So how to call the onCreateView method?
After careful study of the code in the FragmentTabHost we rewritten, we found that there are two main ideas:
The first is to add judgment when calling ft.show. If it is recycled and displayed again, call ft.attch, but there is a problem with this, that is, if there are more tabs, you need to mark the tabHost Which Fragments have been Attch, and which have not been Attached, the logic is more complicated.
Another way is to tell tabHost to clear the previously cached Fragment address after our host Activity has been recycled and rebuilt. In this way, Fragment will be recreated when we switch tabs, and the problem will be solved naturally.
Finally, after weighing and comparing, I decided to use the second way to solve the problem.
Ideas to realize:
1. Add a boolean field in our own rewritten FragmentTabHost class: isRestored,
2. Set this field to true in the screen recovery and reconstruction method
3. Use this field to judge in the doTabChanged method. If it is true, clear the fragment object cache of other tabs in the tabHost class except the tab to be displayed.
The core code is as follows:
/**
* 防止画面回收后重启白屏
*/
private boolean isRestored; @Override
protected void onRestoreInstanceState(Parcelable state) {
SavedState ss = (SavedState)state;
super.onRestoreInstanceState(ss.getSuperState());
setCurrentTabByTag(ss.curTab);
// 防止画面被回收后Fragment白屏
isRestored = true;
}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);
}
// 防止画面被回收后Fragment白屏
if (isRestored) {
if (mTabs != null && mTabs.size() > 0) {
for (int i=0; i<mTabs.size(); i++) {
TabInfo tab = mTabs.get(i);
if (!tab.tag.equals(mLastTab.tag)) {
tab.fragment = null;
}
}
}
isRestored = false;
}
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;
}The complete class code is as follows:
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 net.proding.module.base.BaseFragment;
import java.util.ArrayList;
import java.util.List;
/**
* 用于改善切换tab时不用重新加载
*/
public class CommonFragmentTabHost 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;
/**
* 防止画面回收后重启白屏
*/
private boolean isRestored;
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 CommonFragmentTabHost(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 CommonFragmentTabHost(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.FILL_PARENT,
ViewGroup.LayoutParams.FILL_PARENT));
TabWidget tw = new TabWidget(context);
tw.setId(android.R.id.tabs);
tw.setOrientation(TabWidget.HORIZONTAL);
ll.addView(tw, new LinearLayout.LayoutParams(
ViewGroup.LayoutParams.FILL_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.FILL_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.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.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);
}
}
}
// 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);
// 防止画面被回收后Fragment白屏
isRestored = true;
}
@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);
}
// 防止画面被回收后Fragment白屏
if (isRestored) {
if (mTabs != null && mTabs.size() > 0) {
for (int i=0; i<mTabs.size(); i++) {
TabInfo tab = mTabs.get(i);
if (!tab.tag.equals(mLastTab.tag)) {
tab.fragment = null;
}
}
}
isRestored = false;
}
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;
}
public void reloadTabFragment(String tabId) {
List<Fragment> fragments = mFragmentManager.getFragments();
if(fragments == null) return;
for (Fragment f : fragments){
if(f != null && f.getArguments() != null && tabId.equals(f.getArguments().getString("tabId"))){
((BaseFragment) f).reload();
}
}
}
public Fragment getFragment(String tabId) {
List<Fragment> fragments = mFragmentManager.getFragments();
Fragment fragment = null;
if(fragments == null) return fragment;
for (Fragment f : fragments){
if(f != null && f.getArguments() != null && tabId.equals(f.getArguments().getString("tabId"))){
fragment = f;
break;
}
}
return fragment;
}
}The pro-test problem has been resolved. Friends who are short of time can directly carry out the doctrine to the end.
Thank you!