更改设备方向时，在onCreate()中更改EditText的值无效 [英] Changing the value of an EditText inside onCreate() has no effect when changing device orientation

问题描述

我的理解是，当您更改设备方向时，您的应用会被破坏并重新创建.这意味着onCreate()应该在每次旋转设备时运行.

My understanding is that when you change the device orientation, your app gets destroyed and created again. This means that onCreate() should run every time I rotate the device.

我试图在每次创建应用程序时(包括在屏幕旋转时)设置一个EditText.因此，我启动了该应用程序，并且文本字段显示"Bap".然后，我将该字段的内容更改为"Boop"，然后旋转屏幕.我希望该字段现在说"Bap"，但事实并非如此，它仍然保持我更改后，方向更改之前的状态.为什么会这样?

I'm trying to set an EditText every time the app is created, including whenever the screen is rotated. So, I start up the app, and the text field says "Bap". I then change the contents of the field to "Boop", then rotate the screen. I would expect the field to now say "Bap", but it doesn't, it remains whatever it was after I changed it, before the orientation change. Why is this?

我的onCreate()看起来像这样:

My onCreate() looks like this:

@Override
public void onCreate(Bundle savedInstanceState)
{    
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);

    EditText editText = (EditText)findViewById(R.id.edit_message);
    editText.setText("Bap", TextView.BufferType.EDITABLE);
}

值得注意的是，如果将setText()调用移到onResume()上，一切都会按我期望的那样工作，并且每次旋转设备时都会重置文本字段.

It's worth noting that if I move the setText() call into onResume(), everything works as I would expect it to, with the text field resetting every time I rotate the device.

注意:我意识到提出了类似的问题，但给出的答案并不能真正解释为什么会发生这种行为.

NOTE: I realize a similar question has been asked, but the answer given doesn't really explain why this behaviour is occuring.

推荐答案

之所以发生这种情况，是因为Android框架正在执行应有的功能.它将保存一个捆绑包(SavedInstanceState)，其中包含有关应用程序当前状态的所有信息，以便在方向更改后重新创建视图时使用.

It is happening because the Android framework is doing what it is supposed to. It is saving a bundle (SavedInstanceState) with all the information on the current state of your app, to be used when it re-creates your view after the orientation change.

您是否在发布的onCreate中遗漏了一些代码?也许像这样:

Did you leave some code out of the onCreate you posted? Maybe something like:

if (savedInstanceState == null)

如果将onCreate代码包裹在一个if中，这就是为什么看不到预期结果的原因.

If your onCreate code is wrapped in an if like that, that is why you are not seeing the results you expect.

具有如下所示的onCreate是标准做法:

It is standard practice to have an onCreate that looks like this:

public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);

    if (savedInstanceState == null) {
                // Your first time start-up code here, will not run on orientation change   
    }
            // Any code you want to run EVERY time onCreate runs goes here
}

这样做是为了避免不必要地在方向改变时重新创建所有内容.

This is done so you don't needlessly re-create everything on an orientation change.

希望这会有所帮助！

编辑

进一步研究，似乎正在发生什么(摘录自这里):

Looking into it further, it looks like what is happening is this (gleaned from here):

设备方向更改

onSaveInstanceState(Bundle outState)
onPause()
onStop()
onDestroy()
onCreate()
onStart()
onRestoreInstanceState(Bundle inState)
onResume()

基本上是说，捆绑软件将传递给onRestoreInstanceState，该文件发生在onCreate之后，这将说明您的情况.

It's basically saying that the bundle is getting passed to onRestoreInstanceState, which occurs after onCreate, which would explain what is happening in your case.

因此，解决方案是将EditText值的设置移动到您的onResume方法(或覆盖onRestoreInstanceState).

So, the solution would be to move the setting of the EditText value to your onResume method (or overriding onRestoreInstanceState ).

这篇关于更改设备方向时，在onCreate()中更改EditText的值无效的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！