android編程裏如何使用按鈕來增加和減少進度條的進度

package?com.example.progressbardemo;

import?android.app.Activity;

import?android.os.Bundle;

import?android.view.View;

import?android.view.View.OnClickListener;

import?android.widget.Button;

import?android.widget.ProgressBar;

public?class?MainActivity?extends?Activity?{

private?ProgressBar?one;

private?Button?button;

private?int?i=0;

@Override

protected?void?onCreate(Bundle?savedInstanceState)?{

super.onCreate(savedInstanceState);

setContentView(R.layout.activity_main);

one=(ProgressBar)findViewById(R.id.progressBar2);

button=(Button)findViewById(R.id.button1);

button.setOnClickListener(new?OnClickListener()?{

@Override

public?void?onClick(View?arg0)?{

if(i==0){

one.setVisibility(View.VISIBLE);

}

else?if(i<one.getMax())

{

one.setProgress(i);

}

else

{

one.setVisibility(View.GONE);

i=0;

}

i+=5;

}

});

}

}