java - EditText 自动保存设备旋转后的值

Question

我在 Android Studio 中创建了一个示例应用程序来了解 Android 应用程序的生命周期。我知道方向改变会完全重新启动 Activity (即再次调用 OnCreate 方法)。 据我所知，方向改变应该破坏上下文并在设备旋转后显示空白文本。但不知何故，在不覆盖 onSaveInstanceState 和 onRestoreInstanceState 方法的情况下，它正在保存上下文。

我没有任何 fragment 。它只是 Android Studio 提供的基本模板，几乎没有覆盖生命周期方法。 这是我的 MainActivity 类:

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>

机器人 list :

<?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:

Answer 1

因为 EditText 是一个焦点 View ，所以在 PhoneWindow 中，它的状态将自动保存在 saveHierarchyState() 方法中。可以看到代码:

@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 EditTextView 的 ID:

    <?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>

你会看到你想要的! (来自@Mike M. 的补充坦克)