有以下几种情况：
1.
setContentView(R.layout.activity_list);
requestWindowFeature(Window.FEATURE_NO_TITLE);
修改方法：
requestWindowFeature(Window.FEATURE_NO_TITLE);
setContentView(R.layout.activity_list);
2.在dialog.show()方法前调用了dialog.setContentView()或者dialog.getWindow()
dialog.setContentView(R.layout.activity_main); //或者是调用了 dialog.getWindow();
dialog.show();
修改方法：
dialog.show();
dialog.setContentView(R.layout.activity_main);
3. ***activity继承了ActionBarActivity，然后调用requestWindowFeature(Window.FEATURE_NO_TITLE);报异常
修改方法：使***activity继承自 Activity