android 返回 弹出对话框 确认退出

privatevoiddialog(){
AlertDialog.Builderbuilder=newBuilder(PPTSoftwareActivity.this);
builder.setMessage("确认要退出么？");
builder.setTitle("提示");
builder.setPositiveButton("确定",newDialogInterface.OnClickListener(){

publicvoidonClick(DialogInterfacedialog,intwhich){
//TODOAuto-generatedmethodstub
dialog.dismiss();
finish();
}
});
builder.setNegativeButton("取消",newDialogInterface.OnClickListener(){

publicvoidonClick(DialogInterfacedialog,intwhich){
//TODOAuto-generatedmethodstub
dialog.dismiss();
}
});
builder.show();
}

@Override
publicbooleanonKeyDown(intkeyCode,KeyEventevent){
//TODOAuto-generatedmethodstub
if(keyCode==KeyEvent.KEYCODE_BACK){
dialog();
}
returnfalse;
}