Android 片段生命周期优于方向变化

你把你的碎片一片一片地叠在一起。

当发生配置更改时，旧的片段在重新创建时将自身添加到新的活动中。这是一个巨大的痛苦，在后方的大部分时间。

你可以通过使用相同的片段而不是重新创建一个新的片段来阻止错误的发生:

if (savedInstanceState == null) {
// only create fragment if activity is started for the first time
mFragmentManager = getSupportFragmentManager();
FragmentTransaction fragmentTransaction = mFragmentManager.beginTransaction();


FragmentOne fragment = new FragmentOne();


fragmentTransaction.add(R.id.fragment_container, fragment);
fragmentTransaction.commit();
} else {
// do nothing - fragment is recreated automatically
}

但是要注意: 当生命周期发生微妙变化时，如果您尝试从片段内部访问活动视图，就会出现问题。(从片段中获取父活动的视图并不容易)。

您可以使用 onSaveInstanceState()来 @Override片段活动。请确保不要在方法中调用 super.onSaveInstanceState()。

我们应该总是尝试防止空指针异常，因此我们必须首先在 saveinstance 方法中检查捆绑包信息。查看这个博客 链接的简要说明

public static class DetailsActivity extends Activity {


@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);


if (getResources().getConfiguration().orientation
== Configuration.ORIENTATION_LANDSCAPE) {
// If the screen is now in landscape mode, we can show the
// dialog in-line with the list so we don't need this activity.
finish();
return;
}


if (savedInstanceState == null) {
// During initial setup, plug in the details fragment.
DetailsFragment details = new DetailsFragment();
details.setArguments(getIntent().getExtras());
getFragmentManager().beginTransaction().add(android.R.id.content, details).commit();
}
}
}

引用 这本书，“以确保 一致的用户体验时，Android 会保留片段布局和相关的回栈 由于配置更改，活动将重新启动。”

And the way to approach that is to first check if the Fragment back stack has already been populated, and create the new fragment instance only if it hasn't:

@Override
public void onCreate(Bundle savedInstanceState) {


...


FragmentOne fragment = (FragmentOne) mFragmentManager.findFragmentById(R.id.fragment_container);


if (fragment == null) {
FragmentTransaction fragmentTransaction = mFragmentManager.beginTransaction();
fragmentTransaction.add(R.id.fragment_container, new FragmentOne());
fragmentTransaction.commit();
}
}

如您所见，活动的 onCreate ()方法在方向更改之后调用。因此，不要执行在活动方向更改后添加片段的 FragmentTransaction。

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
if (savedInstanceState==null) {
//do your stuff
}
}

碎片应该而且必须保持不变。

如果你只是做一个项目，然后项目经理说你需要实现切换功能屏幕，但你不想屏幕切换负载不同的布局(可以创建布局和布局端口系统。

You will automatically determine the screen state, load the corresponding layout), because of the need to re initialize the activity or fragment, the user experience is not good, not directly on the screen switch, I refer to ? Url = YgNfP-vHy-Nuldi7YHTfNet3AtLdN-w _ _ O3z1wLOnzr3wDjYo7X7PYdNyhw8R24ZE22xiKnydni7R0r35s2fOLcHOiLGYT9Qh _ fjqtytJki & wd = & eqid = f258719e0001f240000004585a1082

前提是你的布局使用权重的方式布局，布局的权重如下:

<LinearLayout
Android:id= "@+id/toplayout"
Android:layout_width= "match_parent"
Android:layout_height= "match_parent"
Android:layout_weight= "2"
Android:orientation= "horizontal" >

所以我的方法是，当屏幕切换时，不需要加载新的视图文件布局，修改 onConfigurationChanged 动态权重中的布局，下面的步骤: 第一个集合: activity 属性中的 AndroidManifest.xml: android: configChanges = “ keyboardHidden |  方向 | screen Size” 要防止屏幕切换，请避免重新加载，以便能够在 onConfigurationChanged 中进行监视 2在 onConfigurationChanged 方法中重写活动或片段。

@Override
Public void onConfigurationChanged (Configuration newConfig) {
Super.onConfigurationChanged (newConfig);
SetContentView (R.layout.activity_main);
if (newConfig.orientation == Configuration.ORIENTATION_LANDSCAPE) {
//On the layout / / weight adjustment
LinearLayout toplayout = (LinearLayout) findViewById (R.id.toplayout);
LinearLayout.LayoutParams LP = new LayoutParams(LinearLayout.LayoutParams.MATCH_PARENT, 0, 2.0f);
Toplayout.setLayoutParams (LP);
LinearLayout tradespace_layout = (LinearLayout) findViewById(R.id.tradespace_layout);
LinearLayout.LayoutParams LP3 = new LayoutParams(LinearLayout.LayoutParams.MATCH_PARENT, 0, 2.8f);
Tradespace_layout.setLayoutParams (LP3);
}
else if (newConfig.orientation == Configuration.ORIENTATION_PORTRAIT)
{
//On the layout / / weight adjustment
LinearLayout toplayout = (LinearLayout) findViewById (R.id.toplayout);
LinearLayout.LayoutParams LP = new LayoutParams (LinearLayout.LayoutParams.MATCH_PARENT, 0, 2.8f);
Toplayout.setLayoutParams (LP);
LinearLayout tradespace_layout = (LinearLayout) findViewById (R.id.tradespace_layout);
LinearLayout.LayoutParams LP3 = new LayoutParams (LinearLayout.LayoutParams.MATCH_PARENT, 0, 2.0f);
Tradespace_layout.setLayoutParams (LP3);
}
}

在配置更改时，框架将为您创建片段的新实例并将其添加到活动中。所以不是这样:

FragmentOne fragment = new FragmentOne();


fragmentTransaction.add(R.id.fragment_container, fragment);

这样做:

if (mFragmentManager.findFragmentByTag(FRAG1_TAG) == null) {
FragmentOne fragment = new FragmentOne();


fragmentTransaction.add(R.id.fragment_container, fragment, FRAG1_TAG);
}

请注意，除非调用 setRetainInstance (true) ，否则框架将在方向更改时添加一个新的 FragmentOne 实例，在这种情况下，它将添加旧的 FragmentOne 实例。