Android fragment回退栈

男娘i 2022-04-23 02:24 430阅读 0赞

**前言**

Activity切换时，是通过栈的形式，不断压栈出栈。对于fragment如果你不手动开启**回退栈**，它是直接销毁再重建，但如果将fragment任务添加到回退栈，情况就会不一样了，它就有了类似Activity的栈管理方式。

**回顾**

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM3OTgyODIz_size_16_color_FFFFFF_t_70][]

**一、fragment回退栈方法简介**

addToBackStack(tag); 将Fragment添加到回退栈中  
popBackStack(); 清除回退栈中栈顶的Fragment  
popBackStack(String tag, int i );

如果i=0,回退到该tag所对应的Fragment层  
    如果i=FragmentManager.POP\_BACK\_STACK\_INCLUSIVE,回退到该tag所对应的Fragment的上一层

popBackStackImmediate 立即清除回退栈中栈顶Fragment  
getBackStackEntryCount(); 获取回退栈中Fragment的个数  
getBackStackEntryAt(int index) 获取回退栈中该索引值下的Fragment  
举例：逐层退出回退栈效果代码的实现

public class AddFragmentActivity extends FragmentActivity implements MessageFragment.MessageListener {
        private FrameLayout mFrameLayout;
        private RadioGroup mRg;
        private RadioButton mRbHome;
        private RadioButton mRbCommunity;
        private RadioButton mRbMessage;
        private RadioButton mRbMe;
        private List<Fragment> mFragments = new ArrayList<>();
        private HomeFragment homeFragment;
        private CommunityFragment communityFragment;
        private MessageFragment messageFragment;
        private MeFragment meFragment;
        private FragmentManager mSupportFragmentManager;
        private FragmentTransaction mTransaction;
        private TextView mTvMain;
    
        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_fragment);
            mFrameLayout = findViewById(R.id.frameLayout);
            mRg = findViewById(R.id.rg_main);
            mRbHome = findViewById(R.id.rb_home);
            mRbCommunity = findViewById(R.id.rb_community);
            mRbMessage = findViewById(R.id.rb_message);
            mRbMe = findViewById(R.id.rb_me);
            mTvMain = findViewById(R.id.tv_main);
            initView();
       }
    
        private void initView() {
            mSupportFragmentManager = getSupportFragmentManager();
            mTransaction = mSupportFragmentManager.beginTransaction();
            //设置默认选中首页
            mRg.check(R.id.rb_home);
            homeFragment = new HomeFragment();
            //创建Bundle对象，并存储数据
            Bundle bundle = new Bundle();
            bundle.putString("home", "Home");
            homeFragment.setArguments(bundle);
    
            mFragments.add(homeFragment);
            hideOthersFragment(homeFragment, true, "homefragment");
            mRg.setOnCheckedChangeListener(new RadioGroup.OnCheckedChangeListener() {
                @Override
                public void onCheckedChanged(RadioGroup group, int checkedId) {
                    switch (checkedId) {
                        case R.id.rb_home: //首页
                            hideOthersFragment(homeFragment, false, "homefragment");
                            break;
                        case R.id.rb_community: //发现
                            if (communityFragment == null) {
                                communityFragment = new CommunityFragment();
                                Bundle bundle = new Bundle();
                                bundle.putString("community", "Community");
                                communityFragment.setArguments(bundle);
                                mFragments.add(communityFragment);
                                hideOthersFragment(communityFragment, true, "communityfragment");
                            } else {
                                hideOthersFragment(communityFragment, false, "communityfragment");
                            }
                            communityFragment.sendMessage(new ICommuntyCallBack() {
                                @Override
                                public void getMessageFromCommunty(String community) {
                                    mTvMain.setText(community);
                                }
                            });
                            break;
                        case R.id.rb_message: //信息
                            if (messageFragment == null) {
                                messageFragment = new MessageFragment();
                                Bundle bundle = new Bundle();
                                bundle.putString("message", "Message");
                                messageFragment.setArguments(bundle);
                                mFragments.add(messageFragment);
                                hideOthersFragment(messageFragment, true, "messagefragment");
                            } else {
                                hideOthersFragment(messageFragment, false, "messagefragment");
                            }
                            break;
                        case R.id.rb_me: //我的
                            if (meFragment == null) {
                                meFragment = new MeFragment();
                                Bundle bundle = new Bundle();
                                bundle.putString("me", "Me");
                                meFragment.setArguments(bundle);
                                mFragments.add(meFragment);
                                hideOthersFragment(meFragment, true, "mefragment");
                            } else {
                                hideOthersFragment(meFragment, false, "mefragment");
                            }
                            meFragment.sendMessage(new IMeCallBack() {
                                @Override
                                public void getMessageFromMe(String me) {
                                    mTvMain.setText(me);
                                }
                            });
                            break;
                    }
                }
            });
        }
    
        private void hideOthersFragment(Fragment showFragment, boolean add, String tag) {
            mTransaction = mSupportFragmentManager.beginTransaction();
            if (add) {
                mTransaction.add(R.id.frameLayout, showFragment, tag);
                //根据标记添加到回退栈
                mTransaction.addToBackStack(tag);
                Log.i("TAG", "当前添加的fragment是：" + tag);
    
            }
    
            for (Fragment fragment : mFragments) {
                if (showFragment.equals(fragment)) {
                    mTransaction.show(fragment);
                } else {
                    mTransaction.hide(fragment);
                }
            }
    
            mTransaction.commit();
        }
    
        @Override
        public boolean onKeyDown(int keyCode, KeyEvent event) {
            if (keyCode == KeyEvent.KEYCODE_BACK) {
                int count = mSupportFragmentManager.getBackStackEntryCount();
                Log.i("TAG", "获取当前回退栈中fragment的个数是：" + count);
                if (count > 1) {
                    mSupportFragmentManager.popBackStackImmediate();//回退一步清除回退栈中栈顶Fragment
                    //获取当前退到了哪一个Fragment上，重新获取当前的Fragment回退栈中的个数
                    int currentCount = mSupportFragmentManager.getBackStackEntryCount() - 1;
                    Log.i("TAG", "剩余fragment个数是：" + currentCount);
                    FragmentManager.BackStackEntry backStackEntryAt = mSupportFragmentManager.getBackStackEntryAt(mSupportFragmentManager.getBackStackEntryCount()-1);
                    String tag = backStackEntryAt.getName();
                    Log.i("TAG", "当前栈顶的fragment：" + tag);
                    if ("homefragment".equals(tag)) {
                        mRbHome.setChecked(true);
                    } else if ("communityfragment".equals(tag)) {
                        mRbCommunity.setChecked(true);
    
                    } else if ("messagefragment".equals(tag)) {
                        mRbMessage.setChecked(true);
                    } else if ("mefragment".equals(tag)) {
                        mRbMe.setChecked(true);
                    }
                   //mSupportFragmentManager.popBackStackImmediate();//回退一步清除回退栈中栈顶Fragment
                } else {
                    finish();//回退栈中只剩一个Fragment时，退出应用
                }
            }
            return true;
        }
    }

**退出其他所有的frament,只剩首页fragment:只需修改以下代码**

@Override
        public boolean onKeyDown(int keyCode, KeyEvent event) {
            if (keyCode == KeyEvent.KEYCODE_BACK) {
                int count = mSupportFragmentManager.getBackStackEntryCount();
                //回退栈中至少有多个Fragment，栈底部是首页
                if(count>1){
                   while(mSupportFragmentManager.getBackStackEntryCount()>1){
                       mSupportFragmentManager.popBackStackImmediate();
                       //选中第一个界面
                       mRbHome.setChecked(true);
                   }
                }else{
                    finish();
                }
            return true;
        }

**在当前的fragment，点击返回键，直接退出整个activity**

@Override
        public boolean onKeyDown(int keyCode, KeyEvent event) {
            if (keyCode == KeyEvent.KEYCODE_BACK) {
                for (int i = 0; i < count; ++i) {
                    mSupportFragmentManager.popBackStack();
                    finish();
                }
            return true;
        }

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