Fragment事务及Fragment实现选项卡功能

川长思鸟来 2022-07-24 06:16 134阅读 0赞

## Fragment事务 ##

Fragment类引入到Honeycomb时，为协同工作，Activity类被更改为含有FragmentManager类，FragmentManager类负责管理fragment并将它们的视图添加到activity的视图层级结构中。

\-  
FragmentManager类具体管理的是：  
**1. fragment队列**  
**2. fragment事务的回退栈**

\-  
fragment事务被用来 **添加、移除、附加、分离或替换** fragment队列中的fragment。这是使用fragment在运行时组装和重新组装用户界面的核心方式。FragmentManager管理者fragment事务的回退栈。

\-  
FragmentManager.beginTransaction()方法创建并返回FragmentTransaction实例。FragmentTransaction类使用了一个fluent interface接口方法，通过该方法配置FragmentTransaction返回FragmentTransaction类对象，而不是void，由此可得到一个FragmentTransaction队列。

\-  
activity因设备旋转或回收内存被销毁后重建时，Activity.onCreate()方法会响应activity重建而被调用。activity被销毁时，它的FragmentManager会将fragment队列保存下来。这样，activity重建时，新的FragmentManager会首先获取保存的队列，然后重建fragment队列，从而恢复到原来的状态。

## Fragment实现选项卡功能 ##

![2vxv4a9.png][]

package com.ashzheng.studydemo.demo4;
    
    import android.app.Activity;
    import android.app.FragmentManager;
    import android.app.FragmentTransaction;
    import android.os.Bundle;
    import android.widget.RadioGroup;
    
    import com.ashzheng.studydemo.R;
    
    public class Demo4Activity extends Activity {
        private Demo4Fragment1 fragment1;
        private Demo4Fragment2 fragment2;
        private Demo4Fragment3 fragment3;
        private Demo4Fragment4 fragment4;
    
        private FragmentManager fragmentManager;
    
        private RadioGroup radioGroup;
    
        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_demo4);
    
            radioGroup = (RadioGroup) findViewById(R.id.demo4_rg);
            radioGroup.setOnCheckedChangeListener(new RadioGroup.OnCheckedChangeListener() {
                @Override
                public void onCheckedChanged(RadioGroup radioGroup, int i) {
                    selectFragment(i);
                }
            });
    
            fragmentManager = getFragmentManager();
            selectFragment(R.id.demo4_rbt3);
        }
    
    
        private void selectFragment(int checkedId) {
    
            FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
            hideFragment(fragmentTransaction);
    
            switch (checkedId) {
                case R.id.demo4_rbt1:
                    if (null == fragment1) {
                        fragment1 = new Demo4Fragment1();
                        fragmentTransaction.add(R.id.demo4_layout, fragment1);
                    } else {
                        fragmentTransaction.show(fragment1);
                    }
                    break;
                case R.id.demo4_rbt2:
                    if (null == fragment2) {
                        fragment2 = new Demo4Fragment2();
                        fragmentTransaction.add(R.id.demo4_layout, fragment2);
                    } else {
                        fragmentTransaction.show(fragment2);
                    }
                    break;
                case R.id.demo4_rbt3:
                    if (null == fragment3) {
                        fragment3 = new Demo4Fragment3();
                        fragmentTransaction.add(R.id.demo4_layout, fragment3);
                    } else {
                        fragmentTransaction.show(fragment3);
                    }
                    break;
                case R.id.demo4_rbt4:
                    if (null == fragment4) {
                        fragment4 = new Demo4Fragment4();
                        fragmentTransaction.add(R.id.demo4_layout, fragment4);
                    } else {
                        fragmentTransaction.show(fragment4);
                    }
                    break;
            }
            fragmentTransaction.commit();
        }
    
        private void hideFragment(FragmentTransaction fragmentTransaction) {
            if(null != fragment1){
                fragmentTransaction.hide(fragment1);
            }
            if(null != fragment2){
                fragmentTransaction.hide(fragment2);
            }
            if(null != fragment3){
                fragmentTransaction.hide(fragment3);
            }
            if(null != fragment4){
                fragmentTransaction.hide(fragment4);
            }
    
        }
    
    }

[2vxv4a9.png]: http://i.imgur.com/2vxv4a9.png