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[英]onSaveInstanceState/onRestoreInstanceState and view state
[英]Overriding View.onSaveInstanceState() and View.onRestoreInstanceState() using View.BaseSavedState?
假设您希望从现有的View实现派生自己的View类,添加一些值,从而维护一些以有意义的方式表示View状态的变量。
如果您的View会像其他人一样自动保存其状态(如果分配了ID),那么您可能希望覆盖onRestoreInstanceState()
和onSaveInstanceState()
。
当然,您需要调用基类的相应方法,并且需要将状态信息与基类的信息组合在一起。
显然,唯一安全的方法是将超类' Parcelable
包装在一个自己的Parcelable
这样键就不会混淆了。
现在有View.BaseSavedState
及其有趣getSuperState()
方法,但我有点不明白这是如何真正增加价值,只是存储基类的Parcelable
的Bundle
与派生视图的状态值一起并返回。 另一方面,也许某些其他系统组件会期望所有InstanceState信息都是View.AbsSavedState
类型(例如,可以调用getSuperState()
)?
您愿意分享的任何经历?
为了补充James Chen的答案, 这里有一个完整的例子,说明如何使用这种方法,基于查尔斯哈利的博客文章 。
链接代码:
public class LockCombinationPicker extends LinearLayout {
private NumberPicker numberPicker1;
private NumberPicker numberPicker2;
private NumberPicker numberPicker3;
public LockCombinationPicker(Context context) {
this(context, null);
}
public LockCombinationPicker(Context context, AttributeSet attrs) {
this(context, attrs, 0);
}
public LockCombinationPicker(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
loadViews();
}
private void loadViews() {
LayoutInflater.from(getContext()).inflate(R.layout.lock_combination_picker, this, true);
numberPicker1 = (NumberPicker) findViewById(R.id.number1);
numberPicker1.setMinValue(0);
numberPicker1.setMaxValue(10);
numberPicker2 = (NumberPicker) findViewById(R.id.number2);
numberPicker2.setMinValue(0);
numberPicker2.setMaxValue(10);
numberPicker3 = (NumberPicker) findViewById(R.id.number3);
numberPicker3.setMinValue(0);
numberPicker3.setMaxValue(10);
}
@Override
protected Parcelable onSaveInstanceState() {
Parcelable superState = super.onSaveInstanceState();
return new SavedState(superState, numberPicker1.getValue(), numberPicker2.getValue(), numberPicker3.getValue());
}
@Override
protected void onRestoreInstanceState(Parcelable state) {
SavedState savedState = (SavedState) state;
super.onRestoreInstanceState(savedState.getSuperState());
numberPicker1.setValue(savedState.getNumber1());
numberPicker2.setValue(savedState.getNumber2());
numberPicker3.setValue(savedState.getNumber3());
}
@Override
protected void dispatchSaveInstanceState(SparseArray<Parcelable> container) {
// As we save our own instance state, ensure our children don't save and restore their state as well.
super.dispatchFreezeSelfOnly(container);
}
@Override
protected void dispatchRestoreInstanceState(SparseArray<Parcelable> container) {
/** See comment in {@link #dispatchSaveInstanceState(android.util.SparseArray)} */
super.dispatchThawSelfOnly(container);
}
/**
* Convenience class to save / restore the lock combination picker state. Looks clumsy but once created is easy to maintain and use.
*/
protected static class SavedState extends BaseSavedState {
private final int number1;
private final int number2;
private final int number3;
private SavedState(Parcelable superState, int number1, int number2, int number3) {
super(superState);
this.number1 = number1;
this.number2 = number2;
this.number3 = number3;
}
private SavedState(Parcel in) {
super(in);
number1 = in.readInt();
number2 = in.readInt();
number3 = in.readInt();
}
public int getNumber1() {
return number1;
}
public int getNumber2() {
return number2;
}
public int getNumber3() {
return number3;
}
@Override
public void writeToParcel(Parcel destination, int flags) {
super.writeToParcel(destination, flags);
destination.writeInt(number1);
destination.writeInt(number2);
destination.writeInt(number3);
}
public static final Parcelable.Creator<SavedState> CREATOR = new Creator<SavedState>() {
public SavedState createFromParcel(Parcel in) {
return new SavedState(in);
}
public SavedState[] newArray(int size) {
return new SavedState[size];
}
};
}
}
我认为设计需要我们,顾名思义,实现View.BaseSavedState的子类来通过覆盖Parcelable的接口来存储值。
TextView.SavedState就是一个很好的例子
public static class SavedState extends BaseSavedState {
int selStart;
int selEnd;
CharSequence text;
boolean frozenWithFocus;
CharSequence error;
SavedState(Parcelable superState) {
super(superState);
}
@Override
public void writeToParcel(Parcel out, int flags) {
super.writeToParcel(out, flags);
out.writeInt(selStart);
out.writeInt(selEnd);
out.writeInt(frozenWithFocus ? 1 : 0);
TextUtils.writeToParcel(text, out, flags);
if (error == null) {
out.writeInt(0);
} else {
out.writeInt(1);
TextUtils.writeToParcel(error, out, flags);
}
}
@Override
public String toString() {
String str = "TextView.SavedState{"
+ Integer.toHexString(System.identityHashCode(this))
+ " start=" + selStart + " end=" + selEnd;
if (text != null) {
str += " text=" + text;
}
return str + "}";
}
@SuppressWarnings("hiding")
public static final Parcelable.Creator<SavedState> CREATOR
= new Parcelable.Creator<SavedState>() {
public SavedState createFromParcel(Parcel in) {
return new SavedState(in);
}
public SavedState[] newArray(int size) {
return new SavedState[size];
}
};
private SavedState(Parcel in) {
super(in);
selStart = in.readInt();
selEnd = in.readInt();
frozenWithFocus = (in.readInt() != 0);
text = TextUtils.CHAR_SEQUENCE_CREATOR.createFromParcel(in);
if (in.readInt() != 0) {
error = TextUtils.CHAR_SEQUENCE_CREATOR.createFromParcel(in);
}
}
}
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