ListView 适配器的优化分析

以通讯卫士黑名单为例进行分析：

1.当适配器作如下配置的时候：

private class CallSmsSafeAdapter extends BaseAdapter {
    @Override
    public int getCount() {
	return infos.size();
    }
    @Override
    public View getView(final int position, View convertView,ViewGroup parent) {
	Log.i(TAG, "创建新的View对象" + position);
	View view = View.inflate(getApplicationContext(),R.layout.list_callsmssafe_item, null);
	TextView tv_number = (TextView) view.findViewById(R.id.tv_number);
	TextView tv_mode = (TextView) view.findViewById(R.id.tv_mode);
	ImageView iv_delete = (ImageView) view.findViewById(R.id.iv_delete);
			
	String number = infos.get(position).getNumber();
	tv_number.setText(number);
	String mode = infos.get(position).getMode();
	if ("1".equals(mode)) {
	} else if ("2".equals(mode)) {
	    tv_mode.setText("短信拦截");
	} else if ("3".equals(mode)) {
	    tv_mode.setText("电话+短信拦截");
	}
	return view;
    }
    @Override
    public Object getItem(int position) {
	return null;
    }
    @Override
    public long getItemId(int position) {
	return 0;
    }
}

2.每次都新创建一个ListView对象，产生大量的内存垃圾，很快就产生OutOfMemoryError,因此要对内存缓存加以复用！

代码做如下调整：

private class CallSmsSafeAdapter extends BaseAdapter {
    private TextView tv_number;
    private TextView tv_mode;
    private ImageView iv_delete;
    @Override
    public int getCount() {
	return infos.size();
    }
    @Override
    public View getView(final int position, View convertView,ViewGroup parent) {
	View view;
	// 为了减少view对象创建的个数，使用历史缓存
	// convertView instanceof RelativeLayout,这里都是同种缓存可以不写
	if(convertView!=null && convertView instanceof RelativeLayout) {
	    Log.i(TAG, "使用历史缓存的View对象" + position);
	    view = convertView;
	} else {
	    Log.i(TAG, "创建新的View对象" + position);
	    view = View.inflate(getApplicationContext(),R.layout.list_callsmssafe_item, null);
	    tv_number = (TextView) view.findViewById(R.id.tv_number);
	    tv_mode = (TextView) view.findViewById(R.id.tv_mode);
	    iv_delete = (ImageView) view.findViewById(R.id.iv_delete);
	}
		
	String number = infos.get(position).getNumber();
	tv_number.setText(number);
	String mode = infos.get(position).getMode();
	if ("1".equals(mode)) {
	} else if ("2".equals(mode)) {
    	    tv_mode.setText("短信拦截");
	} else if ("3".equals(mode)) {
	    tv_mode.setText("电话+短信拦截");
	}
	    return view;
    }
    @Override
    public Object getItem(int position) {
	return null;
    }
    @Override
    public long getItemId(int position) {
	return 0;
    }
}

3.使用历史缓存后优化性能已经很高，但是每次还是要执行如下查询的代码，还有进一步优化的空间。

tv_number = (TextView) view.findViewById(R.id.tv_number);
tv_mode = (TextView) view.findViewById(R.id.tv_mode);
iv_delete = (ImageView) view.findViewById(R.id.iv_delete);

查询一次后将其信息保存，以后再查询就不必遍历所有控件。

优化如下：

private class CallSmsSafeAdapter extends BaseAdapter {
	
    private TextView tv_number;
    private TextView tv_mode;
    private ImageView iv_delete;
	
    @Override
    public int getCount() {
	return infos.size();
    }
	
    @Override
    public View getView(final int position, View convertView,ViewGroup parent) {
	View view;
	ViewHolder holder;
	// 为了减少view对象创建的个数，使用历史缓存
	// convertView instanceof RelativeLayout,这里都是同种缓存可以不写
	if(convertView!=null && convertView instanceof RelativeLayout) {
       	    Log.i(TAG, "使用历史缓存的View对象" + position);
	    view = convertView;
       	    holder = (ViewHolder) view.getTag();//取出记事本查找
	} else {
	    Log.i(TAG, "创建新的View对象" + position);
	    holder = new ViewHolder();// 买了一个笔记本，记录孩子信息
            view = View.inflate(getApplicationContext(),R.layout.list_callsmssafe_item, null);
	    holder.tv_number = (TextView) view.findViewById(R.id.tv_number);
	    holder.tv_mode = (TextView) view.findViewById(R.id.tv_mode);
	    holder.iv_delete = (ImageView) view.findViewById(R.id.iv_delete);
	    view.setTag(holder);// 把记事本放在口袋
	}
			
	String number = infos.get(position).getNumber();
	holder.tv_number.setText(number);
	String mode = infos.get(position).getMode();
	if ("1".equals(mode)) {
	} else if ("2".equals(mode)) {
  	    holder.tv_mode.setText("短信拦截");
	} else if ("3".equals(mode)) {
	    holder.tv_mode.setText("电话+短信拦截");
	}
	return view;
    }
    @Override
    public Object getItem(int position) {
	return null;
    }
	
    @Override
    public long getItemId(int position) {
        return 0;
    }
}
	
private class ViewHolder {
    private TextView tv_number;
    private TextView tv_mode;
    private ImageView iv_delete;
}

至此，ListView适配器优化完成。