<style name="Dialog_Fullscreen">
    <item name="android:windowFullscreen">true</item>
    <item name="android:windowNoTitle">true</item>
</style>

AlertDialog shareDialog = new AlertDialog.Builder(MyGalleryActivity.this,R.style.Dialog_Fullscreen).setView(R.layout.activity_share
 
).create();
Window shareWindow = shareDialog.getWindow();
shareWindow.setGravity(Gravity.BOTTOM);
WindowManager.LayoutParams lp = shareWindow.getAttributes();
WindowManager m = MyGalleryActivity.this.getWindowManager();
Display d = m.getDefaultDisplay(); // 獲取螢幕寬、高用
lp.height = (int) (d.getHeight() * 0.6
 
); // 高度設定為螢幕的0.6
shareWindow.setAttributes(lp);
shareDialog.show();