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;
 }