Android：Fragment（1）—Fragment布局页面跳转

有关Fragment

Fragment比Activity较轻量级，也可以提供与用户交互的界面并且有自己的生命周期，也不用在Manifest.xml中注册但它必须嵌套在Activity中使用。之前需要使用多个Activity显示的内容，现在可以用一个Activity嵌套多个Fragment来实现。

Fragment的生命周期

Fragment的生命周期不是从new Fragment()开始的，而是从Fragment增加到Activity开始的。

例：Fragment布局页面跳转

布局如下：

布局代码

1.activity_main.xml

2.fragment_one.xml

3.fragment_two.xml

java代码

总体思路如下：
1.先创建类继承Fragment 准备布局 fragment实现onCreateView
2.显示fragment到activity
静态： 在xml布局文件中写标签
动态： FragmentManager 获得 FragmentTransaction
//添加fragment
fragmentTransaction.replace(R.id.line1,fragmentOne);
//把fragment加入到后台栈
fragmentTransaction.addToBackStack(“two”);
//从后台栈移除fragment
FragmentManager.popBackStack();

1.先创建类继承Fragment

准备布局 fragment实现onCreateView
FragmentOne代码：

 import android.app.Fragment;
import android.os.Bundle;
import android.support.annotation.Nullable;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
public class FragmentOne  extends Fragment{
    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        return inflater.inflate(R.layout.fragment_one,null);
    }
}

FragmentTwo代码：

import android.app.Fragment;
import android.os.Bundle;
import android.support.annotation.Nullable;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
/**
 * Created by sq on 2020/2/10.
 */
public class FragmentTwo extends Fragment {

    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        return inflater.inflate(R.layout.fragment_two,null);
    }
}

2.显示fragment到activity

采用动态： FragmentManager 获得 FragmentTransaction
//添加fragment
fragmentTransaction.replace(R.id.line1,fragmentOne);
//把fragment加入到后台栈
fragmentTransaction.addToBackStack(“two”);
//从后台栈移除fragment
FragmentManager.popBackStack();

MainActivity代码

import android.app.FragmentManager;
import android.app.FragmentTransaction;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;

public class MainActivity extends AppCompatActivity {
    private Button one,two;
    FragmentManager fm;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        one = (Button) findViewById(R.id.one);
        two = (Button) findViewById(R.id.second);

        fm = getFragmentManager();

        fm.addOnBackStackChangedListener(new FragmentManager.OnBackStackChangedListener() {
            @Override
            public void onBackStackChanged() {
                Log.i("message","@@"+fm.getBackStackEntryCount());
            }
        });

        /*one.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {

                FragmentOne fragmentOne = new FragmentOne();

                FragmentTransaction fragmentTransaction = fm.beginTransaction();
                //  p1  放在哪个布局里
                fragmentTransaction.replace(R.id.line1,fragmentOne);

                fragmentTransaction.commit();
            }
        });

        two.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                FragmentTwo fragmentTwo = new FragmentTwo();

                FragmentTransaction fragmentTransaction = fm.beginTransaction();
                //  p1  放在哪个布局里
                fragmentTransaction.replace(R.id.line1,fragmentTwo);

                fragmentTransaction.commit();
            }
        });*/
    }

    public void click(View view){
        int id = view.getId();
        FragmentTransaction fragmentTransaction = fm.beginTransaction();
        switch(id){
            case R.id.one:

                FragmentOne fragmentOne = new FragmentOne();
                //  p1  放在哪个布局里
                fragmentTransaction.replace(R.id.line1,fragmentOne);

                fragmentTransaction.addToBackStack("one");
                break;
            case R.id.second:

                FragmentTwo fragmentTwo = new FragmentTwo();
                //  p1  放在哪个布局里
                fragmentTransaction.replace(R.id.line1,fragmentTwo);

                fragmentTransaction.addToBackStack("two");

                break;
            case R.id.back:
                fm.popBackStack();
                break;
        }
        fragmentTransaction.commit();
    }
}