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

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();
}
});
}

报错：Unable to add window token null is not for an application

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