三种方法

第一种：静态fragment

如果是在layout文件中定义的fragment，则使用

getSupportFragmentManager().findFragmentById();

第二种：动态fragment

如果还在程序中代码变更了fragment，则使用

getSupportFragmentManager().findFragmentByTag();

第三种：使用ViewPager装载的fragment

如果使用ViewPager装载fragment时，则需要修改Adapter

定义SmartFragmentStatePagerAdapter.java

import android.support.v4.app.Fragment;import android.support.v4.app.FragmentManager;import android.support.v4.app.FragmentStatePagerAdapter;import android.util.SparseArray;import android.view.ViewGroup;/* Extension of FragmentStatePagerAdapter which intelligently caches all active fragments and manages the fragment lifecycles. Usage involves extending from SmartFragmentStatePagerAdapter as you would any other PagerAdapter.*/public abstract class SmartFragmentStatePagerAdapter extends FragmentStatePagerAdapter {    // Sparse array to keep track of registered fragments in memory    private SparseArray registeredFragments = new SparseArray();    public SmartFragmentStatePagerAdapter(FragmentManager fragmentManager) {        super(fragmentManager);    }    // Register the fragment when the item is instantiated    @Override    public Object instantiateItem(ViewGroup container, int position) {        Fragment fragment = (Fragment) super.instantiateItem(container, position);        registeredFragments.put(position, fragment);        return fragment;    }    // Unregister when the item is inactive    @Override    public void destroyItem(ViewGroup container, int position, Object object) {        registeredFragments.remove(position);        super.destroyItem(container, position, object);    }    // Returns the fragment for the position (if instantiated)    public Fragment getRegisteredFragment(int position) {        return registeredFragments.get(position);    }}

将SectionsPagerAdapter继承于SmartFragmentStatePagerAdapter

/**     * A {@link FragmentPagerAdapter} that returns a fragment corresponding to     * one of the sections/tabs/pages.     */    public class SectionsPagerAdapter extends SmartFragmentStatePagerAdapter {        public SectionsPagerAdapter(FragmentManager fm) {            super(fm);        }        @Override        public Fragment getItem(int position) {            // getItem is called to instantiate the fragment for the given page.            // Return a PlaceholderFragment (defined as a static inner class below).            switch (position) {                case 0:                    return Fragment1.newInstance(position);                case 1:                    return Fragment2.newInstance(position);                default:                    return null;            }        }        @Override        public int getCount() {            // Show 2 total pages.            return 2;        }        @Override        public CharSequence getPageTitle(int position) {            switch (position) {                case 0:                    return "SECTION 0";                case 1:                    return "SECTION 1";            }            return null;        }    }

在onCreate()等中加入初始化代码

mSmartFragmentStatePagerAdapter = new SectionsPagerAdapter(getSupportFragmentManager());// Set up the ViewPager with the sections adapter.mViewPager = (ViewPager) findViewById(R.id.fragment_container);mViewPager.setAdapter(mSmartFragmentStatePagerAdapter);

使用的时候只需下面的代码即可

((Fragment1) mSmartFragmentStatePagerAdapter.getRegisteredFragment(1));

android activity向fragment通信，获取fragment的三种方法

三种方法

第一种：静态fragment

第二种：动态fragment

第三种：使用ViewPager装载的fragment

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