Android Adapter, Observer, and androidobserver

Android Adapter, Observer, and androidobserver

Adapter detail: http://blog.csdn.net/jjwwmlp456/article/details/39893723

Observer (Observer) Detail: http://blog.csdn.net/jjwwmlp456/article/details/39967021

AdapterView System

The Adapter is used in AdapterView.

Adapter system

BaseAdapter implements the SpinnerAdapter and ListAdapter

This is the application in the adapter mode. The interface adapter is used here.

Observer (Observer) Mode

The method for registering and unregistering DataSetObserver is defined in the Adapter.

public interface Adapter {      void registerDataSetObserver(DataSetObserver observer);    void unregisterDataSetObserver(DataSetObserver observer);    ...}

public abstract class DataSetObserver {    public void onChanged() {        // Do nothing    }    public void onInvalidated() {        // Do nothing    }}

public abstract class BaseAdapter implements ListAdapter, SpinnerAdapter {    private final DataSetObservable mDataSetObservable = new DataSetObservable();    public void registerDataSetObserver(DataSetObserver observer) {        mDataSetObservable.registerObserver(observer);    }    public void unregisterDataSetObserver(DataSetObserver observer) {        mDataSetObservable.unregisterObserver(observer);    }    public void notifyDataSetChanged() {        mDataSetObservable.notifyChanged();    }    public void notifyDataSetInvalidated() {        mDataSetObservable.notifyInvalidated();    }    ...}

public class DataSetObservable extends Observable<DataSetObserver> {    public void notifyChanged() {        synchronized(mObservers) {            for (int i = mObservers.size() - 1; i >= 0; i--) {                mObservers.get(i).onChanged();            }        }    }    public void notifyInvalidated() {        synchronized (mObservers) {            for (int i = mObservers.size() - 1; i >= 0; i--) {                mObservers.get(i).onInvalidated();            }        }    }}

public abstract class Observable<T> {    protected final ArrayList<T> mObservers = new ArrayList<T>();    public void registerObserver(T observer) {        if (observer == null) {            throw new IllegalArgumentException("The observer is null.");        }        synchronized(mObservers) {            if (mObservers.contains(observer)) {                throw new IllegalStateException("Observer " + observer + " is already registered.");            }            mObservers.add(observer);        }    }    public void unregisterObserver(T observer) {        if (observer == null) {            throw new IllegalArgumentException("The observer is null.");        }        synchronized(mObservers) {            int index = mObservers.indexOf(observer);            if (index == -1) {                throw new IllegalStateException("Observer " + observer + " was not registered.");            }            mObservers.remove(index);        }    }    public void unregisterAll() {        synchronized(mObservers) {            mObservers.clear();        }    }}

DataSetObserver observer (observed Dataset: changed onChanged, invalid onInvalidated)

Observable processes The Observer (add, remove, register, and unregister)

DataSetObservable extends Observable <DataSetObserver> added two methods to notify data changes and invalid methods.

In AdapterView

class AdapterDataSetObserver extends DataSetObserver {        private Parcelable mInstanceState = null;        @Override        public void onChanged() {            mDataChanged = true;            mOldItemCount = mItemCount;            mItemCount = getAdapter().getCount();            // Detect the case where a cursor that was previously invalidated has            // been repopulated with new data.            if (AdapterView.this.getAdapter().hasStableIds() && mInstanceState != null                    && mOldItemCount == 0 && mItemCount > 0) {                AdapterView.this.onRestoreInstanceState(mInstanceState);                mInstanceState = null;            } else {                rememberSyncState();            }            checkFocus();            requestLayout();        }        @Override        public void onInvalidated() {            mDataChanged = true;            if (AdapterView.this.getAdapter().hasStableIds()) {                // Remember the current state for the case where our hosting activity is being                // stopped and later restarted                mInstanceState = AdapterView.this.onSaveInstanceState();            }            // Data is invalid so we should reset our state            mOldItemCount = mItemCount;            mItemCount = 0;            mSelectedPosition = INVALID_POSITION;            mSelectedRowId = INVALID_ROW_ID;            mNextSelectedPosition = INVALID_POSITION;            mNextSelectedRowId = INVALID_ROW_ID;            mNeedSync = false;            checkFocus();            requestLayout();        }        public void clearSavedState() {            mInstanceState = null;        }    }

Custom AdapterDataSetObserver. requestLayout () is called in both implementation methods, and layout is reset.

The whole process of observing the interface changes caused by data changes:
1. Customize AdapterDataSetObserver in the AdapterView system, and register it (that is, add observer to observable ).

2. After adapter. notifyDataSetChanged () is called, execute the notifyChanged () of observable internally (),

The onChanged () of each observer is executed to update the interface.

NotifyDataSetInvalidated is the same

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