设备自动旋转后，EditText会保存该值

问题描述：

我在Android Studio中创建了一个示例应用程序，以了解Android应用程序的生命周期.我知道方向更改会完全重新启动活动(即再次调用OnCreate方法). 据我所知，方向更改应该会破坏上下文并在设备旋转后显示空白文本.但是以某种方式不覆盖onSaveInstanceState和onRestoreInstanceState方法，它可以保存上下文.

I created a sample application in Android Studio to learn about the life cycle of an Android application. I know that orientation change completely restarts the activity (i.e. OnCreate method is called again). As far as I know, orientation change should have destroyed the context and shown a blank text after device rotation. But somehow without overriding onSaveInstanceState and onRestoreInstanceState methods it is saving the context.

我没有任何碎片.它只是Android Studio提供的基本模板，几乎没有覆盖的生命周期方法. 这是我的MainActivity类:

I don't have any fragments. It just the basic template that is provided by Android studio, with few overridden life cycle methods. Here is my MainActivity class:

package com.example.android.a2_screen_orientation_change;

import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.util.Log;

public class MainActivity extends AppCompatActivity {

    private static final String TAG = MainActivity.class.getSimpleName();

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
    }

    @Override
    protected void onStart() {
        super.onStart();
        Log.i(TAG, "in method onStart");
    }

    @Override
    protected void onResume() {
        super.onResume();
        Log.i(TAG, "in method onResume");
    }

    @Override
    protected void onRestart() {
        super.onRestart();
        Log.i(TAG, "in method onRestart");
    }

    @Override
    protected void onPause() {
        super.onPause();
        Log.i(TAG, "in method onPause");
    }

    @Override
    protected void onStop() {
        super.onStop();
        Log.i(TAG, "in method onStop");
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        Log.i(TAG, "in method onDestroy");
    }
}

布局:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="com.example.android.a2_screen_orientation_change.MainActivity">

    <EditText
        android:id="@+id/editText"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" />

</LinearLayout>

AbdroidManifest:

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.android.a2_screen_orientation_change">

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>

图片:

答

由于EditText是焦点视图，因此在PhoneWindow中，其状态将自动保存在saveHierarchyState()方法中.您可以看到以下代码:

Because the EditText is a focused view, so in PhoneWindow, it's state will be saved automatically in saveHierarchyState() method. You can see the code:

@Override
public Bundle saveHierarchyState() {
    Bundle outState = new Bundle();
    if (mContentParent == null) {
        return outState;
    }
    SparseArray<Parcelable> states = new SparseArray<Parcelable>();
    mContentParent.saveHierarchyState(states);
    outState.putSparseParcelableArray(VIEWS_TAG, states);
    // save the focused view id
    View focusedView = mContentParent.findFocus();
    if (focusedView != null) {
        if (focusedView.getId() != View.NO_ID) {
            outState.putInt(FOCUSED_ID_TAG, focusedView.getId());
        } else {
            if (false) {
                Log.d(TAG, "couldn't save which view has focus because the focused view "
                        + focusedView + " has no id.");
            }
        }
    }
    // save the panels
    SparseArray<Parcelable> panelStates = new SparseArray<Parcelable>();
    savePanelState(panelStates);
    if (panelStates.size() > 0) {
        outState.putSparseParcelableArray(PANELS_TAG, panelStates);
    }
    if (mActionBar != null) {
        outState.putBoolean(ACTION_BAR_TAG, mActionBar.isOverflowMenuShowing());
    }
    return outState;
}

和TextView中的代码:

@Override
public Parcelable onSaveInstanceState() {
    Parcelable superState = super.onSaveInstanceState();
    // Save state if we are forced to
    final boolean freezesText = getFreezesText();
    boolean hasSelection = false;
    int start = -1;
    int end = -1;
    if (mText != null) {
        start = getSelectionStart();
        end = getSelectionEnd();
        if (start >= 0 || end >= 0) {
            // Or save state if there is a selection
            hasSelection = true;
        }
    }
    if (freezesText || hasSelection) {
        SavedState ss = new SavedState(superState);
        if (freezesText) {
            if (mText instanceof Spanned) {
                final Spannable sp = new SpannableStringBuilder(mText);
                if (mEditor != null) {
                    removeMisspelledSpans(sp);
                    sp.removeSpan(mEditor.mSuggestionRangeSpan);
                }
                ss.text = sp;
            } else {
                ss.text = mText.toString();
            }
        }
        if (hasSelection) {
            // XXX Should also save the current scroll position!
            ss.selStart = start;
            ss.selEnd = end;
        }
        if (isFocused() && start >= 0 && end >= 0) {
            ss.frozenWithFocus = true;
        }
        ss.error = getError();
        if (mEditor != null) {
            ss.editorState = mEditor.saveInstanceState();
        }
        return ss;
    }
    return superState;
}

因此，如果您在xml文件中删除了EditTextView的ID，则:

So, if you remove the id of the EditTextView in your xml file:

    <?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="com.example.android.a2_screen_orientation_change.MainActivity">

    <EditText
        android:layout_width="match_parent"
        android:layout_height="wrap_content" />

</LinearLayout>

您将看到想要的东西！ (来自@Mike M的补充罐)

You will see what you want! (Tanks for supplement from @Mike M.)

设备自动旋转后，EditText会保存该值

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