samples/training/AnimationsDemo/src/com/example/android/animationsdemo/CrossfadeActivity.java

/*
 * Copyright 2012 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.animationsdemo;

import android.animation.Animator;
import android.animation.AnimatorListenerAdapter;
import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.support.v4.app.NavUtils;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;

/**
 * This sample demonstrates cross-fading between two overlapping views.
 *
 * <p>In this sample, the two overlapping views are a loading indicator and some text content. The
 * active view is toggled by touching the toggle button in the action bar. In real-world
 * applications, this toggle would occur as soon as content was available. Note that if content is
 * immediately available, a loading spinner shouldn't be presented and there should be no
 * animation.</p>
 */
public class CrossfadeActivity extends Activity {
    /**
     * The flag indicating whether content is loaded (text is shown) or not (loading spinner is
     * shown).
     */
    private boolean mContentLoaded;

    /**
     * The view (or view group) containing the content. This is one of two overlapping views.
     */
    private View mContentView;

    /**
     * The view containing the loading indicator. This is the other of two overlapping views.
     */
    private View mLoadingView;

    /**
     * The system "short" animation time duration, in milliseconds. This duration is ideal for
     * subtle animations or animations that occur very frequently.
     */
    private int mShortAnimationDuration;

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

        mContentView = findViewById(R.id.content);
        mLoadingView = findViewById(R.id.loading_spinner);

        // Initially hide the content view.
        mContentView.setVisibility(View.GONE);

        // Retrieve and cache the system's default "short" animation time.
        mShortAnimationDuration = getResources().getInteger(android.R.integer.config_shortAnimTime);
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        super.onCreateOptionsMenu(menu);
        getMenuInflater().inflate(R.menu.activity_crossfade, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        switch (item.getItemId()) {
            case android.R.id.home:
                // Navigate "up" the demo structure to the launchpad activity.
                // See http://developer.android.com/design/patterns/navigation.html for more.
                NavUtils.navigateUpTo(this, new Intent(this, MainActivity.class));
                return true;

            case R.id.action_toggle:
                // Toggle whether content is loaded.
                mContentLoaded = !mContentLoaded;
                showContentOrLoadingIndicator(mContentLoaded);
                return true;
        }

        return super.onOptionsItemSelected(item);
    }

    /**
     * Cross-fades between {@link #mContentView} and {@link #mLoadingView}.
     */
    private void showContentOrLoadingIndicator(boolean contentLoaded) {
        // Decide which view to hide and which to show.
        final View showView = contentLoaded ? mContentView : mLoadingView;
        final View hideView = contentLoaded ? mLoadingView : mContentView;

        // Set the "show" view to 0% opacity but visible, so that it is visible
        // (but fully transparent) during the animation.
        showView.setAlpha(0f);
        showView.setVisibility(View.VISIBLE);

        // Animate the "show" view to 100% opacity, and clear any animation listener set on
        // the view. Remember that listeners are not limited to the specific animation
        // describes in the chained method calls. Listeners are set on the
        // ViewPropertyAnimator object for the view, which persists across several
        // animations.
        showView.animate()
                .alpha(1f)
                .setDuration(mShortAnimationDuration)
                .setListener(null);

        // Animate the "hide" view to 0% opacity. After the animation ends, set its visibility
        // to GONE as an optimization step (it won't participate in layout passes, etc.)
        hideView.animate()
                .alpha(0f)
                .setDuration(mShortAnimationDuration)
                .setListener(new AnimatorListenerAdapter() {
                    @Override
                    public void onAnimationEnd(Animator animation) {
                        hideView.setVisibility(View.GONE);
                    }
                });
    }
}