android AlertDialog或toast显示错误 Unable to add window token null is not for an application解决办法

android.view.WindowManager$BadTokenException: Unable to add window – token android.os.xxx is not valid; is your activity running?

android app的bug统计工具中常遇会记录到这个异常，错误的代码如下：

  public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    findViewById(R.id.button1).setOnClickListener(new Button.OnClickListener() {
        
        public void onClick(View v) {
            new AlertDialog.Builder(getApplicationContext())
            .setTitle(R.string.dialogTitle)
            .setMessage(R.string.dialogMessage)
            .setPositiveButton("确定", new DialogInterface.OnClickListener() {
                public void onClick(DialogInterface dialog, int which) {
                    Toast.makeText(getApplicationContext(), "你按了确定。", Toast.LENGTH_SHORT).show();
                }
            }).show();
        }
    });
}

异常原因：AlertDialog创建语句public AlertDialog.Builder (Context context)中，不能使用getApplicationContext()得到的context，而必须使用Activity，所以解决如下

解决办法：

将 new AlertDialog.Builder(getApplicationContext()) 改为 new AlertDialog.Builder(MainActivity.this)

其中MainActivity 为当前Activity的名称