判断状态栏是否显示以及获取状态栏高度的方法，及工具类列子【续：及OnGlobalLayoutListener的利用】

http://www.jcodecraeer.com/a/anzhuokaifa/androidkaifa/2014/0731/1640.html

本篇博客是http://www.cnblogs.com/longjunhao/p/8973729.html的后续

问题：上篇博客中，如果在onCreate中就需要获取statusbar的高度，当kill进程之后再次进入oncreate时，由于新增的statusBarHelperView还没有绘制完成导致statusbar获取失败。

解决方案：

方案1：在onCreate中调用statusbar时，做个延迟操作。但是这种方案不太好，毕竟是如果手机比较卡的时候可能也会失败

方案2：给statusHelperView增加绘制完的监听：mStatusBarHelperView.getViewTreeObserver().addOnGlobalLayoutListener(mGlobalLayoutListener);当绘制完成后会调用该监听中的onGlobalLayout方法，然后再通过回调，当执行onGlobalLayout时再获取statusbar的高度，在上面博客中的工具类中新增如下方法：

package com.smartisanos.ime.util;

import android.content.Context;
import android.graphics.PixelFormat;
import android.os.Handler;
import android.os.Message;
import android.view.Gravity;
import android.view.View;
import android.view.ViewTreeObserver;
import android.view.WindowManager;

import com.smartisanos.ime.IMEApp;

public class StatusBarHelper {
    private Context mContext;
    private View mStatusBarHelperView;
    private static StatusBarHelper mStatusBarHelper = new StatusBarHelper();
    private static final int MSG_INIT_STATUS_BAR = 1;
    private static final int MSG_REMOVE_STATUS_BAR = 2;
    private static final long MSG_REMOVE_DELAY_TIME = 500L;

    private StatusBarHelperViewLayoutListener mStatusBarHelperViewLayoutListener;

    private Handler mStatusBarHandler = new Handler() {
        @Override
        public void handleMessage(Message msg) {
            switch (msg.what) {
                case MSG_INIT_STATUS_BAR:
                    mStatusBarHandler.removeMessages(MSG_REMOVE_STATUS_BAR);
                    initStatusBarHelperView();
                    break;
                case MSG_REMOVE_STATUS_BAR:
                    removeStatusBarView();
                    break;
            }
        }
    };

    private StatusBarHelper() {
        mContext = IMEApp.getContext();
    }

    public static StatusBarHelper getInstance() {
        return mStatusBarHelper;
    }

    private void initStatusBarHelperView() {
        if (mStatusBarHelperView != null) {
            return;
        }
        WindowManager wm = (WindowManager) mContext.getSystemService(Context.WINDOW_SERVICE);
        mStatusBarHelperView = new View(mContext);
        WindowManager.LayoutParams lp = new WindowManager.LayoutParams();
        lp.flags = WindowManager.LayoutParams.FLAG_NOT_TOUCH_MODAL
                | WindowManager.LayoutParams.FLAG_NOT_TOUCHABLE;
        lp.gravity = Gravity.LEFT | Gravity.TOP;
        lp.type = WindowManager.LayoutParams.TYPE_SYSTEM_OVERLAY;
        lp.format = PixelFormat.TRANSLUCENT;
        mStatusBarHelperView.getViewTreeObserver().addOnGlobalLayoutListener(mGlobalLayoutListener);
        wm.addView(mStatusBarHelperView, lp);
    }

    public void addStatusBarHelperView() {
        Message message = mStatusBarHandler.obtainMessage(StatusBarHelper.MSG_INIT_STATUS_BAR);
        mStatusBarHandler.sendMessage(message);
    }

    public void removeStatusBarHelperView() {
        Message message = mStatusBarHandler.obtainMessage(StatusBarHelper.MSG_REMOVE_STATUS_BAR);
        mStatusBarHandler.sendMessageDelayed(message, StatusBarHelper.MSG_REMOVE_DELAY_TIME);
    }

    public int getStatusBarHeight() {
        if (mStatusBarHelperView == null) {
            return 0;
        }
        int[] windowParams = new int[2];
        int[] screenParams = new int[2];
        mStatusBarHelperView.getLocationInWindow(windowParams);
        mStatusBarHelperView.getLocationOnScreen(screenParams);
        return screenParams[1] - windowParams[1];
    }

    private void removeStatusBarView() {
        if (mStatusBarHelperView != null) {
            mStatusBarHelperView.getViewTreeObserver().removeOnGlobalLayoutListener(mGlobalLayoutListener);
            WindowManager wm = (WindowManager) mContext.getSystemService(Context.WINDOW_SERVICE);
            wm.removeView(mStatusBarHelperView);
            mStatusBarHelperView = null;
        }
    }

    private ViewTreeObserver.OnGlobalLayoutListener mGlobalLayoutListener = new ViewTreeObserver.OnGlobalLayoutListener() {
        @Override
        public void onGlobalLayout() {
            if (mStatusBarHelperViewLayoutListener != null) {
                mStatusBarHelperViewLayoutListener.updateStatusBarHeightWhenGlobalLayout();
            }
        }
    };

    public interface StatusBarHelperViewLayoutListener {
        void updateStatusBarHeightWhenGlobalLayout();
    }

    public void setStatusBarHelperViewLayoutListener(StatusBarHelperViewLayoutListener listener) {
        mStatusBarHelperViewLayoutListener = listener;
    }

    public void onConfigurationChanged() {//此处和本博客无关
        removeStatusBarView();
        initStatusBarHelperView();
    }
}

 这样在onCreate中调用的时候，只需要回调方法即可：

        StatusBarHelper.getInstance().setStatusBarHelperViewLayoutListener(new StatusBarHelper.StatusBarHelperViewLayoutListener() {
        @Override
        public void updateStatusBarHeightWhenGlobalLayout() {
            if (mStatusBarHeight != IMEContext.config().getStatusBarHeight() && isShowing()) {
                mStatusBarHeight = IMEContext.config().getStatusBarHeight();
                //当helpeView绘制完成之后，判断mStatusBarHeight（此全局变量是onCreate中获取的）和新的不相等后，执行相应的操作（eg：update操作）
            }
        }
    });