使用片段添加到后台堆栈的 Android 将无法正常工作

Question

我正在使用片段构建一个计算器应用程序，我希望计算器片段在菜单项片段上按下后退按钮时显示回来。我一直在使用 addToBackStac(null) 但它不适合我。

下面是我的代码

公共类 MainActivity 扩展 ActionBarActivity {

FragmentManager fragmentManager;


protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    if(savedInstanceState == null){
    fragmentManager = getFragmentManager();
    FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction().addToBackStack(null);
    CalculatorFragment calc = new  CalculatorFragment();
    fragmentTransaction.add(R.id.relLejaut, calc);
    fragmentTransaction.commit();
    }

}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    MenuInflater inflater = getMenuInflater();
    inflater.inflate(R.menu.main, menu);
    return super.onCreateOptionsMenu(menu);
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    // Handle action bar item clicks here. The action bar will
    // automatically handle clicks on the Home/Up button, so long
    // as you specify a parent activity in AndroidManifest.xml.
    int id = item.getItemId();
    if (id == R.id.item) {

        About about= new About();
        // Insert the fragment by replacing any existing fragment

        fragmentManager.beginTransaction().addToBackStack(null).replace(R.id.relLejaut, about).commit();



        return true;
    }
    return super.onOptionsItemSelected(item);
}

}

Answer 1

您需要先在 FragmentTransaction 中添加（）或替换（）片段，然后调用 addToBackStack() 使其工作。
这样称呼它：

fragmentManager.beginTransaction().replace(R.id.relLejaut,about).addToBackStack(null).commit();