Dialog(四)——报错Unable to add window -- token null is not for an application

/**
* 问题描述:
* 创建和显示对话框的时候报错
* Unable to add window -- token null is not for an application
*
* 问题修正:
* 不可使用Builder builder=new Builder(getApplicationContext());
* 应该使用Builder builder=new Builder(MainActivity.this);
*/
private void showDialog(){
Dialog dialog;
//正确
Builder builder=new Builder(MainActivity.this);
//错误
//Builder builder=new Builder(getApplicationContext());
builder.setIcon(R.drawable.ic_launcher);
builder.setTitle(getResources().getString(R.string.dialog_title));
builder.setMessage(R.string.dialog_message);
builder.setNegativeButton("取消", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int arg1) {
}
});
builder.setPositiveButton("确定", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int arg1) {
}
});

dialog=builder.create();
dialog.show();
}