AlertDialog.setMessage不显示的问题

        AlertDialog.Builder builder = new AlertDialog.Builder(MainActivity.this);        builder.setMessage("message");        builder.setNegativeButton(getString(R.string.know), new DialogInterface.OnClickListener() {            @Override            public void onClick(DialogInterface dialog, int which) {                dialog.dismiss();            }        });        builder.setPositiveButton(getString(R.string.go_upload), new DialogInterface.OnClickListener() {            @Override            public void onClick(DialogInterface dialog, int which) {                //一些代码            }        });        builder.create().show();

就是如上的代码，发现实际情况messge根本没显示出来。
搞了好久终于找到了解决方法：

给dialog增加主题。修改代码如下：

        AlertDialog.Builder builder = new AlertDialog.Builder(this, R.style.MyAlertDialogStyle);        builder.setMessage(getString(R.string.upload_cover_tips));        builder.setNegativeButton(getString(R.string.know), new DialogInterface.OnClickListener() {            @Override            public void onClick(DialogInterface dialog, int which) {                dialog.dismiss();            }        });        builder.setPositiveButton(getString(R.string.go_upload), new DialogInterface.OnClickListener() {            @Override            public void onClick(DialogInterface dialog, int which) {                QtPhotoDisplayActivity.getInstance().start(MainActivity.this);            }        });        builder.create().show();

    <style name="MyAlertDialogStyle" parent="Theme.AppCompat.Light.Dialog.Alert">        <!-- Used for the buttons -->        <item name="colorAccent">#2196f3</item>        <!-- Used for the title and text -->        <item name="android:textColorPrimary">#000000</item>        <!-- Used for the background -->        <item name="android:background">#FFFFFF</item>    </style>

增加了一个主题样式之后，dialog可以正常的展示了。