/*** Used 自定义Application【系统上下文】*/
public class MyApplication extends Application{/**系统上下文*/private static Context mAppContext;@Overridepublic void onCreate() {super.onCreate();mAppContext = getApplicationContext();}/**获取系统上下文：用于ToastUtil类*/public static Context getAppContext(){return mAppContext;}
}

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"package="com.why.project.toastutildemo"><applicationandroid:allowBackup="true"android:icon="@mipmap/ic_launcher"android:label="@string/app_name"android:supportsRtl="true"android:theme="@style/AppTheme"android:name=".MyApplication"><activity android:name=".activity.MainActivity"><intent-filter><action android:name="android.intent.action.MAIN"/><category android:name="android.intent.category.LAUNCHER"/></intent-filter></activity></application></manifest>

package com.why.project.toastutildemo.util;import android.content.Context;
import android.view.Gravity;
import android.widget.Toast;import com.why.project.toastutildemo.MyApplication;/*** Create By HaiyuKing* Used 简单的Toast封装类*/
public class ToastUtil {private static Toast toast;//实现不管我们触发多少次Toast调用，都只会持续一次Toast显示的时长/*** 短时间显示Toast【居下】* @param msg 显示的内容-字符串*/public static void showShortToast(String msg) {if(MyApplication.getAppContext() != null){if (toast == null) {toast = Toast.makeText(MyApplication.getAppContext(), msg, Toast.LENGTH_SHORT);} else {toast.setText(msg);}//1、setGravity方法必须放到这里，否则会出现toast始终按照第一次显示的位置进行显示（比如第一次是在底部显示，那么即使设置setGravity在中间，也不管用）//2、虽然默认是在底部显示，但是，因为这个工具类实现了中间显示，所以需要还原，还原方式如下：toast.setGravity(Gravity.BOTTOM, 0, dip2px(MyApplication.getAppContext(),64));toast.show();}}/*** 短时间显示Toast【居中】* @param msg 显示的内容-字符串*/public static void showShortToastCenter(String msg){if(MyApplication.getAppContext() != null) {if (toast == null) {toast = Toast.makeText(MyApplication.getAppContext(), msg, Toast.LENGTH_SHORT);} else {toast.setText(msg);}toast.setGravity(Gravity.CENTER, 0, 0);toast.show();}}/*** 短时间显示Toast【居上】* @param msg 显示的内容-字符串*/public static void showShortToastTop(String msg){if(MyApplication.getAppContext() != null) {if (toast == null) {toast = Toast.makeText(MyApplication.getAppContext(), msg, Toast.LENGTH_SHORT);} else {toast.setText(msg);}toast.setGravity(Gravity.TOP, 0, 0);toast.show();}}/*** 长时间显示Toast【居下】* @param msg 显示的内容-字符串*/public static void showLongToast(String msg) {if(MyApplication.getAppContext() != null) {if (toast == null) {toast = Toast.makeText(MyApplication.getAppContext(), msg, Toast.LENGTH_LONG);} else {toast.setText(msg);}toast.setGravity(Gravity.BOTTOM, 0, dip2px(MyApplication.getAppContext(),64));toast.show();}}/*** 长时间显示Toast【居中】* @param msg 显示的内容-字符串*/public static void showLongToastCenter(String msg){if(MyApplication.getAppContext() != null) {if (toast == null) {toast = Toast.makeText(MyApplication.getAppContext(), msg, Toast.LENGTH_LONG);} else {toast.setText(msg);}toast.setGravity(Gravity.CENTER, 0, 0);toast.show();}}/*** 长时间显示Toast【居上】* @param msg 显示的内容-字符串*/public static void showLongToastTop(String msg){if(MyApplication.getAppContext() != null) {if (toast == null) {toast = Toast.makeText(MyApplication.getAppContext(), msg, Toast.LENGTH_LONG);} else {toast.setText(msg);}toast.setGravity(Gravity.TOP, 0, 0);toast.show();}}/*=================================常用公共方法============================*/public static int dip2px(Context context, float dpValue) {final float scale = context.getResources().getDisplayMetrics().density;return (int) (dpValue * scale + 0.5f);}
}

ToastUtil.showShortToast("ToastUtilDemo");//如果显示字符串，直接写即可
ToastUtil.showShortToast(MyApplication.getAppContext().getResources().getString(R.string.app_name));//如果想要显示Strings.xml文件中的字符串，建议使用MyApplication.getAppContext()

if(isAdded()) {//如果该Fragment对象被添加到了它的Activity中，那么它返回true，否则返回false。ToastUtil.showShortToast(MyApplication.getAppContext().getResources().getString(R.string.app_name)); }