Question

在努力使我的简单片段程序工作之后，我没有找到以下任何解决方案：我在我的主要活动中管理两个片段：FragmentNeedle和FragmentPlot。一次只能出现一个。用户有两个句子，他可以选择他想要显示的片段。此外，当FragmentPlot显示时，用户应该能够通过按后退键导航回FragmentNeedle。这是我的代码：

public void onButtonPlotPressed()
{
    FragmentManager manager = getSupportFragmentManager();      
    mPlotFragment = (PlotFragment) manager.findFragmentByTag(PlotFragment.class.getSimpleName());

    if(mPlotFragment == null)
    {
        mPlotFragment = new PlotFragment();
        FragmentTransaction ft = manager.beginTransaction();            
        ft.replace(R.id.main_layout_center, mPlotFragment, PlotFragment.class.getSimpleName());                                                 
        ft.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_OPEN);                               
        ft.addToBackStack(null);
        ft.commit();        
        manager.executePendingTransactions();   
    }

public void OnButtonNeedlePressed()
{
    FragmentManager manager = getSupportFragmentManager();
mFragmentNeedle = (FragmentNeedle) manager.findFragmentByTag(FragmentNeedle.class.getSimpleName()); 


    FragmentTransaction ft = manager.beginTransaction();        
    if(mFragmentNeedle == null)
    {
        mFragmentNeedle= new FragmentNeedle();

        ft.replace(R.id.main_layout_center, mFragmentNeedle,    FragmentNeedle.class.getSimpleName());                                  
        ft.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_OPEN);                    
        ft.commit();            
        manager.executePendingTransactions();   
    }   


}

当显示PlotFragment时，我按回，我将返回NeedleFragment。但现在当我尝试通过按UI按钮更改为Plot Fragment时，它将继续显示PlotFragment。如果我删除了ft.addToBackStack（）行，通过按下UI上的按钮，片段之间的切换工作正常，但是我不能用后退键返回。我做错了什么？

Answer 1

您永远不会将FragmentNeedle添加到后台。

public void OnButtonNeedlePressed() {    
    mFragmentNeedle = (FragmentNeedle)manager.findFragmentByTag(FragmentNeedle.class.getSimpleName()); 

    if(mFragmentNeedle == null) {
        FragmentManager manager = getSupportFragmentManager();
        mFragmentNeedle= new FragmentNeedle();

        ft.replace(R.id.main_layout_center, mFragmentNeedle, FragmentNeedle.class.getSimpleName());                                  
        ft.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_OPEN); 
        //missing line
        ft.addToBackStack(FragmentNeedle.class.getSimpleName());
        ft.commit();            
        manager.executePendingTransactions();   
    }   
}

Android：切换碎片和Backstack

1 个答案: