Fragment基本使用方法

• fragment生命周期

• fragment依赖于Activity

• fragment通过getActivity()获取当前所在的Activity

• fragment通过FragmentManager的findFragmentById()

  或findFragmentByTag()获取fragment

• fragment与activity多对多关系

//第一步，实例化
AFragment aFragment = new AFragment();
//第二步，添加fragment
getFragmentManager().beginTransaction().add(R.id.frame_container, aFragment).commit();
//或者调用，通常调用这个方法不用commit()
getFragmentManager().beginTransaction().add(R.id.frame_container, aFragment).commitAllowingStateLoss();

//getSupportFragment()与getFragmentManager()区别？

getSupportFragmentManager():

3.0以下，3.0以下没有fragment的api，需要V4包通过此方法间接获取FragmentManager()对象，同时继承FragmentActivity,这样才能获取fragment

getFragmentManager():

3.0以上，有了fragment的api，可直接继承Activity获取fragment对象

//问题点commit()与commitAllowingStateLoss()区别？

commit()需要在onSaveInstanceState()之前调用，如果在之后调用就会出现Can not perform this action after onSaveInstanceState异常的提示

commitAllowingStateLoss()则不会进行onSaveInstanceState()保存前后的判断，则不会出现上面的异常提示

if(bFragment == null){
  bFragment = new BFragment();
}
getFragmentManager().beginTransaction().replace(R.id.frame_container, bFragment).commitAllowingStateLoss();

生命周期相关

        //getActivity()可能为null情况
    @Override
    public void onAttach(Context context) {
        super.onAttach(context);
        mActivity = (Activity)context;  //可能会导致内存泄漏,不推荐
    }

    @Override
    public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
        super.onViewCreated(view, savedInstanceState);
        //遇到getActivity()为空的情况解决方案可以先进行非空判断
        if(getActivity() != null){
            //做activity相关操作
        }
    }
}

    //fragment传值的方式
        public static AFragment newInstance(String title){
        AFragment aFragment = new AFragment();
        Bundle bundle = new Bundle();
        bundle.putString("title", title);
        //如果fragment被重新创建，setArgument也不会丢失，系统会通过setArgument重新赋值
        aFragment.setArguments(bundle); 
        return aFragment;
    }

    @Override
    public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
        super.onViewCreated(view, savedInstanceState);
        if(getArguments() != null){
            getArguments().getString("title");  //获取传入的值
        }
    }

//将fragment添加到回退栈中，不至于返回时，只返回到Activity
getFragmentManager().beginTransaction()
  .add(R.id.frame_container, aFragment).addToBackStack(null).commitAllowingStateLoss();

    @Override
    public void onAttach(Context context) {
        super.onAttach(context);
                try {
                        listener = (listenerImpl)context;       //实现activity对fragment当中监听的接口
        } catch (ClassCastException e) {
            e.printStackTrace();
        }
    }
    @Override
    public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
        super.onViewCreated(view, savedInstanceState);
        btn.setOnClickListener(new View.OnClickListener(){
          listener.onClick("进行方法的回调");  //在此对onClick方法在Activity中进行回调
        });
    }