1、先在drawable目录下创建一个渐变色的矩形图片xml文件：com_sswl_gradient_yello.xml

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android"
    android:shape="rectangle">
    <gradient
        android:angle="0"
        android:endColor="@color/com_sswl_yello_f5aa33"
        android:startColor="@color/com_sswl_yello_f88907"
        android:type="linear"/>
</shape>

2、然后在Activity的布局绘制完成之后，即在onWindowFocusChanged

@Override
    public void onWindowFocusChanged(boolean hasFocus) {
        super.onWindowFocusChanged(hasFocus);
            StatusBarUtil.setStatusBarDrawable(this,R.drawable.com_sswl_gradient_yello);
    }

或者在Activity中对窗口的DecorView增加布局变化监听

getWindow().getDecorView().getViewTreeObserver().addOnGlobalFocusChangeListener(new ViewTreeObserver.OnGlobalFocusChangeListener() {
     @Override
     public void onGlobalFocusChanged(View oldFocus, View newFocus) {
        StatusBarUtil.setStatusBarDrawable(this,R.drawable.com_sswl_gradient_yello);        
    }
});

调用反射修改状态栏背景即可

/**
     * 设置状态栏颜色背景图
     * @param activity
     * @param id
     */
    public static void setStatusBarDrawable(Activity activity, @DrawableRes int id) {
        //利用反射机制修改状态栏背景
        int identifier = activity.getResources().getIdentifier("statusBarBackground", "id", "android");
        View statusBarView = activity.getWindow().findViewById(identifier);
        if (statusBarView != null) {
            statusBarView.setBackgroundResource(id);
        }
    }

【备注】
之所以要在onWindowFocusChanged 或者onGlobalFocusChanged 调用，是因为当切换到其他第三方页面或者主题不一致的页面时候，状态栏状态会被覆盖重置掉，所以要重新设置回来才有效