ListView和GridView多次调用GetView的现象和解决办法

背景：以前遇到过，最近又碰到了，就总结一下吧

一.ListView

(1)出现原因

是因为listView的高度不确定，一般用的是wrap_content，导致系统需要不断地测量，也就是多测调用onMeasure方法，所以就多次调用getView,所以解决方法也挺简单，把宽高写死（精确给个数字，或者match_parent）.

(2)解决方法

adapter.java

package com.dx.text0808;

import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.TextView;

import java.util.ArrayList;
import java.util.List;


public class UpdateOtherGridAdapter extends BaseAdapter {
    private LayoutInflater inflater;
    private Context mContext;
    private List contentList = new ArrayList<>();


    public UpdateOtherGridAdapter(Context context, ArrayList list) {
        this.mContext = context;
        inflater = LayoutInflater.from(context);
        this.contentList = list;
    }

    public void setContentList(List contentList) {
        this.contentList = contentList;
    }

    public void update() {
        this.notifyDataSetChanged();
    }

    @Override
    public int getCount() {
        return contentList.size();
    }

    @Override
    public Object getItem(int arg0) {
        return null;
    }

    @Override
    public long getItemId(int arg0) {
        return 0;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        System.out.println("xcqw getView  ***position"+position);
        ViewHolder holder = null;
        if (convertView == null) {
            convertView = inflater.inflate(R.layout.item,
                    parent, false);
            holder = new ViewHolder();
            holder.tvContent = (TextView) convertView.findViewById(R.id.tv_content);
            convertView.setTag(holder);
        } else {
            holder = (ViewHolder) convertView.getTag();
        }

        String content = contentList.get(position);
        holder.tvContent.setText(content);
        return convertView;
    }

    public class ViewHolder {
        public TextView tvContent;
    }


}

<1>会出现多次调用getView的写法

activity_main.xml

注意看到 ListView的Layout_height中写的是wrap_content

实际打印如下：
08-07 16:39:18.604 25086-25086/com.dx.text0808 I/System.out: xcqw getView  ***position0
08-07 16:39:18.609 25086-25086/com.dx.text0808 I/System.out: xcqw getView  ***position1
08-07 16:39:18.609 25086-25086/com.dx.text0808 I/System.out: xcqw getView  ***position2
08-07 16:39:18.668 25086-25086/com.dx.text0808 I/System.out: xcqw getView  ***position0
08-07 16:39:18.669 25086-25086/com.dx.text0808 I/System.out: xcqw getView  ***position1
08-07 16:39:18.679 25086-25086/com.dx.text0808 I/System.out: xcqw getView  ***position2
08-07 16:39:18.691 25086-25086/com.dx.text0808 I/System.out: xcqw getView  ***position0
08-07 16:39:18.693 25086-25086/com.dx.text0808 I/System.out: xcqw getView  ***position1
08-07 16:39:18.707 25086-25086/com.dx.text0808 I/System.out: xcqw getView  ***position2
08-07 16:39:18.784 25086-25086/com.dx.text0808 I/System.out: xcqw getView  ***position0
08-07 16:39:18.785 25086-25086/com.dx.text0808 I/System.out: xcqw getView  ***position1
08-07 16:39:18.786 25086-25086/com.dx.text0808 I/System.out: xcqw getView  ***position2

<2>不会出现多次调用getView的写法

注意看到现在ListView中的Layout_height写的是Match_parent

实际打印如下：

08-07 16:42:48.892 28432-28432/com.dx.text0808 I/System.out: xcqw getView  ***position0
08-07 16:42:48.905 28432-28432/com.dx.text0808 I/System.out: xcqw getView  ***position1
08-07 16:42:48.910 28432-28432/com.dx.text0808 I/System.out: xcqw getView  ***position2

二.GridView

(1)出现原因

貌似不管长宽写不写死都是会多次调用getView，不知道为啥，日了狗了。。。原因待补充

(2)解决方法

<1>出现的情形

adapter.xml

package com.dx.text0807;

import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.TextView;

import java.util.ArrayList;
import java.util.List;


public class UpdateOtherGridAdapter extends BaseAdapter {
    private LayoutInflater inflater;
    private Context mContext;
    private List contentList = new ArrayList<>();


    public UpdateOtherGridAdapter(Context context, ArrayList list) {
        this.mContext = context;
        inflater = LayoutInflater.from(context);
        this.contentList = list;
    }

    public void update() {
        this.notifyDataSetChanged();
    }

    @Override
    public int getCount() {
        return contentList.size();
    }

    @Override
    public Object getItem(int arg0) {
        return null;
    }

    @Override
    public long getItemId(int arg0) {
        return 0;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        System.out.println("xcqw getView  1***position"+position);

        ViewHolder holder = null;
        if (convertView == null) {
            convertView = inflater.inflate(R.layout.item,
                    parent, false);
            holder = new ViewHolder();
            holder.tvContent = (TextView) convertView.findViewById(R.id.tv_content);
            convertView.setTag(holder);
        } else {
            holder = (ViewHolder) convertView.getTag();
        }


        if(((MyGridView) parent).isOnMeasure){
            //如果是onMeasure调用的就立即返回
            return convertView;
        }
        System.out.println("xcqw getView  2***position"+position);

        String content = contentList.get(position);
        holder.tvContent.setText(content);


    //如果不是onMeasure调用的就可以正常操作了
    //赋值操作
        return convertView;
    }

    public class ViewHolder {
        public TextView tvContent;
    }


}

activity_main.xml

注意了！！！，不管你长宽怎么写都是会多次调用getView，不知道网上说写死就可以的人是怎么整的。。。

<2>解决方法

不让他多次调用getView是不可能了，所以只能说在他onMeasure调用getView的时候我们不要去对convertView做任务赋值的操作，只有当onLayout的时候我们再对ConvertView操作

首先我们要重写一个gridView

MyGridView.java

public class MyGridView extends GridView {
    public boolean isOnMeasure;
    public MyGridView(Context context) {
        super(context);
    }

    public MyGridView(Context context, AttributeSet attrs) {
        super(context, attrs);
    }


    public MyGridView(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        isOnMeasure = true;
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
    }

    @Override
    protected void onLayout(boolean changed, int l, int t, int r, int b) {
        isOnMeasure = false;
        super.onLayout(changed, l, t, r, b);
    }
}

getView中对ConvertView的处理

@Override
    public View getView(int position, View convertView, ViewGroup parent) {
        System.out.println("xcqw getView  1***position"+position);

        ViewHolder holder = null;
        if (convertView == null) {
            convertView = inflater.inflate(R.layout.item,
                    parent, false);
            holder = new ViewHolder();
            holder.tvContent = (TextView) convertView.findViewById(R.id.tv_content);
            convertView.setTag(holder);
        } else {
            holder = (ViewHolder) convertView.getTag();
        }


        if(((MyGridView) parent).isOnMeasure){
            //如果是onMeasure调用的就立即返回
            return convertView;
        }
        System.out.println("xcqw getView  2***position"+position);

        String content = contentList.get(position);
        holder.tvContent.setText(content);


    //如果不是onMeasure调用的就可以正常操作了
    //赋值操作
        return convertView;
    }

实际打印

08-07 17:11:37.119 17294-17294/com.dx.text0807 I/System.out: xcqw getView  1***position0
08-07 17:11:37.178 17294-17294/com.dx.text0807 I/System.out: xcqw getView  1***position0
08-07 17:11:37.268 17294-17294/com.dx.text0807 I/System.out: xcqw getView  1***position0
08-07 17:11:37.268 17294-17294/com.dx.text0807 I/System.out: xcqw getView  2***position0
08-07 17:11:37.269 17294-17294/com.dx.text0807 I/System.out: xcqw getView  1***position1
08-07 17:11:37.271 17294-17294/com.dx.text0807 I/System.out: xcqw getView  2***position1
08-07 17:11:37.272 17294-17294/com.dx.text0807 I/System.out: xcqw getView  1***position2
08-07 17:11:37.273 17294-17294/com.dx.text0807 I/System.out: xcqw getView  2***position2
08-07 17:11:37.274 17294-17294/com.dx.text0807 I/System.out: xcqw getView  1***position3
08-07 17:11:37.276 17294-17294/com.dx.text0807 I/System.out: xcqw getView  2***position3
08-07 17:11:37.279 17294-17294/com.dx.text0807 I/System.out: xcqw getView  1***position0
08-07 17:11:37.281 17294-17294/com.dx.text0807 I/System.out: xcqw getView  1***position0
08-07 17:11:37.373 17294-17294/com.dx.text0807 I/System.out: xcqw getView  1***position0
08-07 17:11:37.376 17294-17294/com.dx.text0807 I/System.out: xcqw getView  1***position0

可以看到  getView2***  打印只有四次  ，效果达到了，哈哈