Android性能优化（一）—— 启动优化，冷启动，热启动，温启动

     // Set to false to disable the preview that is shown while a new activity
    // is being started.
    private static final boolean SHOW_APP_STARTING_PREVIEW = true;

    void startActivityLocked(ActivityRecord r, ActivityRecord focusedTopActivity,
            boolean newTask, boolean keepCurTransition, ActivityOptions options) {
       //…… 省略一万行……

        if (!isHomeOrRecentsStack() || numActivities() > 0) {
            if (DEBUG_TRANSITION) Slog.v(TAG_TRANSITION,
                    "Prepare open transition: starting " + r);
            //…… 省略一万行……

            boolean doShow = true;
            if (newTask) {
                // Even though this activity is starting fresh, we still need
                // to reset it to make sure we apply affinities to move any
                // existing activities from other tasks in to it.
                // If the caller has requested that the target task be
                // reset, then do so.
                if ((r.intent.getFlags() & Intent.FLAG_ACTIVITY_RESET_TASK_IF_NEEDED) != 0) {
                    resetTaskIfNeededLocked(r, r);
                    doShow = topRunningNonDelayedActivityLocked(null) == r;
                }
            } else if (options != null && options.getAnimationType()
                    == ActivityOptions.ANIM_SCENE_TRANSITION) {
                doShow = false;
            }
            if (r.mLaunchTaskBehind) {
                // Don't do a starting window for mLaunchTaskBehind. More importantly make sure we
                // tell WindowManager that r is visible even though it is at the back of the stack.
                r.setVisibility(true);
                ensureActivitiesVisibleLocked(null, 0, !PRESERVE_WINDOWS);
            // 如果同时满足，则显示空白屏幕
            } else if (SHOW_APP_STARTING_PREVIEW && doShow) {
                //……
                //显示空白屏幕
                r.showStartingWindow(prev, newTask, isTaskSwitch(r, focusedTopActivity));
            }
        } else {
            // If this is the first activity, don't do any fancy animations,
            // because there is nothing for it to animate on top of.
            ActivityOptions.abort(options);
        }
    }

<resources>
    <!-- Base application theme. -->
    <style name="AppTheme" parent="Theme.AppCompat.Light.DarkActionBar">
        <!-- Customize your theme here. -->
        <item name="colorPrimary">@color/colorPrimary</item>
        <item name="colorPrimaryDark">@color/colorPrimaryDark</item>
        <item name="colorAccent">@color/colorAccent</item>

    </style>

    <!--禁用预览功能主题-->
    <style name="AppSpalshNoPreviewTheme" parent="AppTheme">
        <item name="android:windowFullscreen">true</item>
        <item name="windowNoTitle">true</item>

        <!--        <item name="android:windowContentOverlay">@null</item>-->
        <!--        <item name="android:windowBackground">@mipmap/wall</item>-->
        <item name="android:windowDisablePreview">true</item>
    </style>
</resources>



<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    package="com.margin.myapplication">

<application
    android:allowBackup="true"
    android:icon="@mipmap/ic_launcher"
    android:label="@string/app_name"
    android:roundIcon="@mipmap/ic_launcher_round"
    android:supportsRtl="true"
    android:name=".MyApplication"
    android:theme="@style/AppTheme"
    tools:ignore="GoogleAppIndexingWarning">


    <activity android:name=".SplashActivity"
        android:theme="@style/AppSpalshNoPreviewTheme">
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />

            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
    </activity>

    <activity android:name=".HomeActivity"
        android:launchMode="singleTask"/>
</application>

</manifest>

    <!--替换首屏的背景的主题-->
    <style name="AppSpalshBackgroundTheme" parent="AppTheme">
        <item name="android:windowBackground">@mipmap/wall</item>
        <item name="android:windowFullscreen">true</item>
        <item name="windowNoTitle">true</item>
    </style>

public class MyApplication extends Application {

    @Override
    public void onCreate() {
        super.onCreate();
        try {
            Thread.sleep(1500);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }

    }
}