本文記錄如何實現同個Activity中存在多個Fragment多次切換依次返回之後或者任意返回。

依次返回

思路：自己定義一個棧，將我們每次顯示的Fragment放到我們的棧裡面，想要依次返回的時候就從棧頂開始彈棧，如果想要返回到任意Fragment的時候，就去棧中找到這個Fragment
實現這個需求需要用到Stack這個類了
首先簡單介紹下Stack，首先它是繼承Vector，在Vector基礎上，做了一些拓展，主要方法如下

1,首先需要3個Fragment

public class Fragment1 extends Fragment{

    @Override
    public View onCreateView(LayoutInflater inflater,  ViewGroup container,  Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.fragment1,container,false
 
);
        TextView mTextView = (TextView) view.findViewById(R.id.tv_fragment_content);
        mTextView.setText("Fragment1");
        return view;
    }
}

public class Fragment2 extends Fragment1 {

    @Override
    public View onCreateView(LayoutInflater inflater,  ViewGroup container,  Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.fragment1,container,false
 
);
        TextView mTextView = (TextView) view.findViewById(R.id.tv_fragment_content);
        mTextView.setText("Fragment2");
        return view;
    }
 }

public class Fragment3 extends Fragment1{

    @Override
    public View onCreateView(LayoutInflater inflater,  ViewGroup container,  Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.fragment1,container,false);
        TextView mTextView = (TextView) view.findViewById(R.id.tv_fragment_content);
        mTextView.setText("Fragment3");
        return view;
    }

}

xml：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout           xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"       android:layout_width="match_parent"
android:layout_height="match_parent">
    <TextView
        android:id="@+id/tv_fragment_content"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:gravity="center"
        android:textSize="40sp"
        android:text="--"
        />
</LinearLayout>

有了3個Fragment之後，我們要實現的效果跟之前一樣，依次切換3個Fragment然後通過按返回鍵依次返回之前的Fragment

下面是Activity的程式碼：
為什麼純程式碼寫佈局，因為工作所迫

public class StackActivity extends FragmentActivity {
    private Stack<Fragment> mFragmentStack = new Stack<>();//自己維護要處理Fragment的棧,這麼做的好處是可以靈活的使用裡面儲存的Fragmtnt
    private Fragment mContentFragment,MainFragment;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        LinearLayout mParentLayout = new LinearLayout(this); //最外層佈局
        mParentLayout.setLayoutParams(new LinearLayout.LayoutParams(LinearLayout.LayoutParams.MATCH_PARENT, LinearLayout.LayoutParams.MATCH_PARENT));
        mParentLayout.setOrientation(LinearLayout.VERTICAL);

        LinearLayout mContentLayout = new LinearLayout(this);//內容佈局
        LinearLayout.LayoutParams mContentParams = new LinearLayout.LayoutParams(LinearLayout.LayoutParams.MATCH_PARENT, 0);
        mContentParams.weight = 1;
        mContentLayout.setLayoutParams(mContentParams);
        mContentLayout.setId(R.id.tv_fragment_content);

        Button toggleFragment = new Button(this);//下面按鈕
        toggleFragment.setLayoutParams(new ViewGroup.LayoutParams(ViewGroup.LayoutParams.MATCH_PARENT, dp2px(40)));
        toggleFragment.setText("toggle");
        toggleFragment.setOnClickListener(mToggleClickListener);

        mParentLayout.addView(mContentLayout);
        mParentLayout.addView(toggleFragment);

        Window mWindow = getWindow();
        mWindow.setContentView(mParentLayout);

        MainFragment = new Fragment1();
        mFragmentStack.push(MainFragment);//將元素新增到棧
        getSupportFragmentManager().beginTransaction().add(R.id.tv_fragment_content,MainFragment,"fragment1").commit();    


    }

    /**
     * 切換Fragment 這裡的if條件是防止多次點選相同元素多次進棧
     * 可以根據自己業務靈活變動
     */
    protected View.OnClickListener mToggleClickListener = new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            if(mFragmentStack.size() <= 1){
                mContentFragment = new Fragment2();
                mFragmentStack.push(mContentFragment);//將元素新增到棧
                getSupportFragmentManager().beginTransaction().replace(R.id.tv_fragment_content,mContentFragment,"fragment1").commit(); 
            }else if(mFragmentStack.size() == 2){
                mContentFragment = new Fragment3();
                showStacks(mFragmentStack);
                getSupportFragmentManager().beginTransaction().replace(R.id.tv_fragment_content,mContentFragment,"fragment1").commit();             
            }
        }
    };

    /**
     * 返回鍵
     * 觸發棧裡面的元素彈棧，棧頂開始
     * 這裡因為往棧裡面塞了2個元素所以第一次彈棧的是最後新增的Fragment ->fragment2
     */
    @Override
    public void onBackPressed() { //返回鍵
        if(!mFragmentStack.isEmpty()) {
            mContentFragment = mFragmentStack.pop();
            getSupportFragmentManager().beginTransaction().replace(R.id.tv_fragment_content, mContentFragment, "fragment1").commit();  

        }else
            finish();
    }

    public void showStacks(Stack<Fragment> stack){
        if(stack.size() == 0){
            Log.e("TAG","棧裡面是空的");
        }else{
            Enumeration mEnum = stack.elements();//得到stack中的列舉物件
            while(mEnum.hasMoreElements()){
                Log.e("TAG","elements : "+ mEnum.nextElement());
            }
        }
    }
}
   /**
     * dp轉換為px
     * @param inparam
     * @return
     */
    public int dp2px(float inparam) {
        float destiny = getResources().getDisplayMetrics().density;
        return (int) (destiny * inparam + 0.5f);
    }

這是最基礎的依次返回，也可以按照自己的意願返回到任意Fragment，只要存在在我們的棧中，則可以隨意拿出來使用

任意返回

上面的search方法，這個會返回目標元素到頂端的距離。
然後我們可以用Vector的ElementAt方法來獲取到當前的物件

//這裡只做了直接返回第一個Fragment，其他的沒有處理
    @Override
    public void onBackPressed() { //返回鍵
        if(!mFragmentStack.isEmpty()) {
           mContentFragment = mFragmentStack.elementAt(mFragmentStack.size() - mFragmentStack.search(MainFragment));
            getSupportFragmentManager().beginTransaction().replace(R.id.tv_fragment_content, mContentFragment, "fragment1").commit();
        }else
            finish();
    }