如何使用getView()方法以及调用它的位置？

Question

我是Android开发的新手,并且一直关注Android网站上提供的教程.我目前正在阅读Views的教程部分,特别是Grid Views:Hello,Grid View Tutorial.

我无法理解如何通过适配器进行查看.我知道您必须覆盖适配器类中的getView()方法,并在此方法中定义视图的设置方式.我不明白getView()实际上被调用的地方是什么？也许我在这里有错误的心态,但在下面的代码中(网格视图教程)我没有看到任何对getView()的调用(或适配器类中使用的任何其他东西,如getCount()) .

main.xml中

<?xml version="1.0" encoding="utf-8"?>
<GridView xmlns:android="http://schemas.android.com/apk/res/android" 
    android:id="@+id/gridview"
    android:layout_width="fill_parent" 
    android:layout_height="fill_parent"
    android:columnWidth="90dp"
    android:numColumns="auto_fit"
    android:verticalSpacing="10dp"
    android:horizontalSpacing="10dp"
    android:stretchMode="columnWidth"
    android:gravity="center" />

Start.java

package com.examples.hellogridlayout;

import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.widget.AdapterView;
import android.widget.GridView;
import android.widget.Toast;
import android.widget.AdapterView.OnItemClickListener;

public class Start extends Activity {
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);
    GridView gridview = (GridView)findViewById(R.id.gridview);
    gridview.setAdapter(new ImageAdapter(this));

    gridview.setOnItemClickListener(new OnItemClickListener(){
        public void onItemClick(AdapterView<?> parent,View v, int position, long     id){
            Toast.makeText(Start.this, "" + position,Toast.LENGTH_SHORT).show();
        }

      });
    }
}

ImageAdapter.java

package com.examples.hellogridlayout;

import android.content.Context;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.GridView;
import android.widget.ImageView;

public class ImageAdapter extends BaseAdapter {
    private Context mContext;

    public ImageAdapter(Context c) {
        mContext = c;
    }

    public int getCount() {
    return mThumbIds.length;
    }

    public Object getItem(int position) {
    return null;
    }

    public long getItemId(int position) {
        return 0;
    }

    // create a new ImageView for each item referenced by the Adapter
    public View getView(int position, View convertView, ViewGroup parent) {
        ImageView imageView;
        if (convertView == null) {  // if it's not recycled, initialize some attributes
            imageView = new ImageView(mContext);
            imageView.setLayoutParams(new GridView.LayoutParams(85, 85));
            imageView.setScaleType(ImageView.ScaleType.CENTER_CROP);
            imageView.setPadding(8, 8, 8, 8);
        } else {
            imageView = (ImageView) convertView;
        }

        imageView.setImageResource(mThumbIds[position]);
        return imageView;
    }

    // references to our images
    private Integer[] mThumbIds = {
            R.drawable.sample_2, R.drawable.sample_3,
            R.drawable.sample_4, R.drawable.sample_5,
            R.drawable.sample_6, R.drawable.sample_7,
            R.drawable.sample_0, R.drawable.sample_1,
            R.drawable.sample_2, R.drawable.sample_3,
            R.drawable.sample_4, R.drawable.sample_5,
            R.drawable.sample_6, R.drawable.sample_7,
            R.drawable.sample_0, R.drawable.sample_1,
            R.drawable.sample_2, R.drawable.sample_3,
            R.drawable.sample_4, R.drawable.sample_5,
            R.drawable.sample_6, R.drawable.sample_7
    };
}

Answer 1

通过设置适配器,您告诉GridView从适配器获取视图以填满所有网格.因此getViewGridView内部调用它来填充布局.

这就是为什么所有适配器都实现Adapter 接口,以便任何AdapterView可以请求适配器.

Answer 2

Adapter.getView调用inside ObtainView方法,从GridView父类继承AbsListView,ScrapView对象在可用时传入:

child = mAdapter.getView(position, scrapView, this);

然后直接ObtainView实现,GridView.onMeasure也可以在几个调用的回调中实现GridView.layoutChildren,包括onTouchEvent处理滚动,拖动和其他触摸导航的继承方法.