Android(安卓)Fragment回退栈的使用

现有这样一个场景，从Fragment1跳转到Fragment2再跳转到Fragment3，

如何实现按下回退键直接从Fragment3返回Fragment1？

利用FragmentManager的getBackStackEntryCount() 来获取当前回退栈中Fragment的个数

如果大于1就循环弹出栈顶fragment

具体代码实现

public class FragmentActivity extends AppCompatActivity implements OnReplace {    private FrameLayout frameLayout;    private BlankFragment blankFragment;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_fragment);        frameLayout = (FrameLayout) findViewById(R.id.frameLayout);        fragmentManager = getSupportFragmentManager();        FragmentTransaction transaction = fragmentManager.beginTransaction();        blankFragment  = new BlankFragment();        transaction.add(R.id.frameLayout, blankFragment);        transaction.commit();    }    @Override    public void onBackPressed() {        // 获取当前回退栈中的Fragment个数        int backStackEntryCount = fragmentManager.getBackStackEntryCount();        //如果大于1 就做循环回退        if (backStackEntryCount > 1) {            while (fragmentManager.getBackStackEntryCount() > 0) {                super.onBackPressed();            }        }    }    private FragmentManager fragmentManager;    @Override    public void onReplace(int index) {        final BlankFragment2 blankFragment2 = new BlankFragment2();        final BlankFragment3 blankFragment3 = new BlankFragment3();        switch (index) {            case 1:                fragmentManager.beginTransaction()                        .addToBackStack(null)                        .replace(R.id.frameLayout,blankFragment2)                        .commit();                break;            case 2:                fragmentManager.beginTransaction()                        .replace(R.id.frameLayout,blankFragment3)                        .addToBackStack(null)                        .commit();                break;        }    }}

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