Android example source code file (MyPreference.java)

This example Android source code file (MyPreference.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Android by Example" ^TM.

Java - Android tags/keywords

android, attributeset, basesavedstate, content, creator, integer, mypreference, object, os, override, parcelable, preference, savedstate, textview, ui, utilities

The MyPreference.java Android example source code

/*
 * Copyright (C) 2007 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.example.android.apis.app;

import com.example.android.apis.R;

import android.content.Context;
import android.content.res.TypedArray;
import android.os.Parcel;
import android.os.Parcelable;
import android.preference.Preference;
import android.util.AttributeSet;
import android.view.View;
import android.widget.TextView;

/**
 * This is an example of a custom preference type. The preference counts the
 * number of clicks it has received and stores/retrieves it from the storage.
 */
public class MyPreference extends Preference {
    private int mClickCounter;
    
    // This is the constructor called by the inflater
    public MyPreference(Context context, AttributeSet attrs) {
        super(context, attrs);
        
        setWidgetLayoutResource(R.layout.preference_widget_mypreference);        
    }

    @Override
    protected void onBindView(View view) {
        super.onBindView(view);
        
        // Set our custom views inside the layout
        final TextView myTextView = (TextView) view.findViewById(R.id.mypreference_widget);
        if (myTextView != null) {
            myTextView.setText(String.valueOf(mClickCounter));
        }
    }

    @Override
    protected void onClick() {
        int newValue = mClickCounter + 1;
        // Give the client a chance to ignore this change if they deem it
        // invalid
        if (!callChangeListener(newValue)) {
            // They don't want the value to be set
            return;
        }
        
        // Increment counter
        mClickCounter = newValue;
        
        // Save to persistent storage (this method will make sure this
        // preference should be persistent, along with other useful checks)
        persistInt(mClickCounter);
        
        // Data has changed, notify so UI can be refreshed!
        notifyChanged();
    }

    @Override
    protected Object onGetDefaultValue(TypedArray a, int index) {
        // This preference type's value type is Integer, so we read the default
        // value from the attributes as an Integer.
        return a.getInteger(index, 0);
    }

    @Override
    protected void onSetInitialValue(boolean restoreValue, Object defaultValue) {
        if (restoreValue) {
            // Restore state
            mClickCounter = getPersistedInt(mClickCounter);
        } else {
            // Set state
            int value = (Integer) defaultValue;
            mClickCounter = value;
            persistInt(value);
        }
    }

    @Override
    protected Parcelable onSaveInstanceState() {
        /*
         * Suppose a client uses this preference type without persisting. We
         * must save the instance state so it is able to, for example, survive
         * orientation changes.
         */
        
        final Parcelable superState = super.onSaveInstanceState();
        if (isPersistent()) {
            // No need to save instance state since it's persistent
            return superState;
        }

        // Save the instance state
        final SavedState myState = new SavedState(superState);
        myState.clickCounter = mClickCounter;
        return myState;
    }

    @Override
    protected void onRestoreInstanceState(Parcelable state) {
        if (!state.getClass().equals(SavedState.class)) {
            // Didn't save state for us in onSaveInstanceState
            super.onRestoreInstanceState(state);
            return;
        }
     
        // Restore the instance state
        SavedState myState = (SavedState) state;
        super.onRestoreInstanceState(myState.getSuperState());
        mClickCounter = myState.clickCounter;
        notifyChanged();
    }
    
    /**
     * SavedState, a subclass of {@link BaseSavedState}, will store the state
     * of MyPreference, a subclass of Preference.
     * <p>
     * It is important to always call through to super methods.
     */
    private static class SavedState extends BaseSavedState {
        int clickCounter;
        
        public SavedState(Parcel source) {
            super(source);
            
            // Restore the click counter
            clickCounter = source.readInt();
        }

        @Override
        public void writeToParcel(Parcel dest, int flags) {
            super.writeToParcel(dest, flags);
            
            // Save the click counter
            dest.writeInt(clickCounter);
        }

        public SavedState(Parcelable superState) {
            super(superState);
        }

        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];
            }
        };
    }
    
}