当从片段序列通过 backStack returns 返回到 main activity 时，涉及 Android 生命周期的哪一部分（如果有的话）？

Question

我正在努力学习 Fragment class。这是 MainActivity:

    package com.dslomer64.hour8appflip;

    import android.app.Activity;
    import android.app.FragmentTransaction;
    import android.os.Bundle;
    import android.view.View;
    import android.widget.Button;

    public class MainActivity extends Activity {

        Button btnStartGarcon, btnStartWaiter;

        @Override protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_main);
            btnStartGarcon = (Button)findViewById(R.id.btnStartGarcon);
            btnStartWaiter = (Button)findViewById(R.id.btnStartWaiter);
            ableButtons(true);
        }
        @Override protected void onStart(){
            super.onStart();
            ableButtons(true);
        }
        @Override protected void onRestart(){
            super.onRestart();
            ableButtons(true);
        }
        @Override protected void onResume(){
            super.onResume();
            ableButtons(true);
        }
        public void showFragmentGarcon(){
            FragmentGarcon fragmentGarcon = new FragmentGarcon();
            FragmentTransaction ft = getFragmentManager().beginTransaction();
            ft.replace(R.id.layout_container, fragmentGarcon);
            ft.addToBackStack("Garcon");
            ft.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_FADE);
            ft.commit();
        }
        public void showFragmentWaiter(){
            FragmentWaiter fragmentWaiter = new FragmentWaiter();
            FragmentTransaction ft = getFragmentManager().beginTransaction();
            ft.replace(R.id.layout_container, fragmentWaiter);
            ft.addToBackStack("Waiter");
            ft.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_FADE);
            ft.commit();
        }
        public void onStartGarcon(View view) {
            showFragmentGarcon();
            ableButtons(false);
        }
        public void onStartWaiter(View view) {
            showFragmentWaiter();
            ableButtons(false);
        }
        private void ableButtons(boolean b){
            btnStartWaiter.setEnabled(b);
            btnStartGarcon.setEnabled(b);
        }
    }

启动后，屏幕在左侧。第一次点击按钮后，它在右边，因为我决定最好禁用 MainActivity 按钮。

但是当我点击 back 图标的次数足以耗尽 backStack 时，无论我做什么（参见 onStart 中非常多余的 ableButtons(true)，onRestart onResume), 按钮仍然被禁用。

怎么办？

Answer 1

What part of the Android life cycle is involved (if any) when going back through backStack returns to main activity from a sequence of fragments?

不涉及Activity生命周期。当您替换 Fragment 时，您不会离开 activity，因此您不会 return 它。

But when I tap the back icon enough times to exhause the backStack, no matter what I do (see the very redundant ableButtons(true) in onStart, onRestart onResume), the buttons are still disabled.

这是预期的行为。您禁用了这些按钮，当 backStack 为空时，您可以再次启用它们。例如你可以覆盖 onBackPressed

@Override
public void onBackPressed(){
  int count = getSupportFragmentManager().getBackStackEntryCount(); 

  if (count == 0){
      ableButtons(true);
  } 
    super.onBackPressed();
}

Answer 2

想通了（与Android生命周期无关）：

FragmentManager fm = getFragmentManager();

...

@Override
public void onBackPressed() {
    super.onBackPressed();
    if( fm.getBackStackEntryCount() == 0){
        ableButtons(true);
    }
}

并在 showFragmentGarcon 和另一个 showFrag... 中使用 fm:

  public void showFragmentGarcon(){
        FragmentGarcon fragmentGarcon = new FragmentGarcon();

        FragmentTransaction ft = fm.beginTransaction();
  //                             ^^

当从片段序列通过 backStack returns 返回到 main activity 时，涉及 Android 生命周期的哪一部分（如果有的话）？

What part of the Android life cycle is involved (if any) when going back through backStack returns to main activity from a sequence of fragments?

android

android-lifecycle

android-fragments