Android 開發 (六十二) Drawable mutate

先看一下這段code

public static class MyAdapter extends BaseAdapter {
   private LayoutInflater inflater;

   public MyAdapter(Context context) {
    inflater = LayoutInflater.from(context);
   }

   @Override
   public int getCount() {
    // TODO Auto-generated method stub
    return 10;
   }

   @Override
   public Object getItem(int arg0) {
    // TODO Auto-generated method stub
    return arg0;
   }

   @Override
   public long getItemId(int arg0) {
    // TODO Auto-generated method stub
    return 0;
   }

   @Override
   public View getView(int arg0, View arg1, ViewGroup arg2) {
    View view = inflater.inflate(R.layout.listview_layout, null);
    CheckBox check = (CheckBox) view.findViewById(R.id.check);
    Drawable d= inflater.getContext().getResources()
      .getDrawable(R.drawable.icon_item_small_selected);
    if (arg0 == 1) {
     d.setAlpha(255);
    } else {
     d.setAlpha(70); 
    }
    check.setButtonDrawable(d);

    return view;
   }

  }

看起來非常的正常，只不過是在position為1的時候將透明度改成255其他時候為70
但是結果是如下面這張圖...  我們會發現position 1的透明度竟然不是255.....

這其實是因為當getdrawable取得同一張圖時其實是共用resource而且共用state ，
所以當你針對某一張圖做更改時，其實同時也改到了其他共用的view


那要怎麼解決?    mutate 

接著讓我們將原本的code 加入 mutate

   @Override
   public View getView(int arg0, View arg1, ViewGroup arg2) {
    View view = inflater.inflate(R.layout.listview_layout, null);
    CheckBox check = (CheckBox) view.findViewById(R.id.check);
    Drawable d = inflater.getContext().getResources()
      .getDrawable(R.drawable.icon_item_small_selected);
    if (arg0 == 1) {
     d.mutate().setAlpha(255);
    } else {
     d.mutate().setAlpha(70); 
    }
    check.setButtonDrawable(d);

    return view;
   }

讓我們再看一次結果

everything works.