Question

我在我的应用程序中有一个Gridview，但问题是它再次加载所有图像，因为我滚动导致严重滞后，我怎样才能让它一次加载所有图像并缓存它？

    package com.example.helloworld;

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;

  // Constructor
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) {
  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;
   }

   // Keep all Images in array
  public Integer[] mThumbIds = {
  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_8, 
  R.drawable.sample_9,
  R.drawable.sample_10, 
  R.drawable.sample_11,
  R.drawable.sample_12, 
  R.drawable.sample_13,
  R.drawable.sample_14, 
  R.drawable.sample_15,
  R.drawable.sample_16, 
  R.drawable.sample_17  

  };
   }

Answer 1

如果你查看方法setImageResource的文档，它说它可能会导致用户界面缓慢。该文档提供了另一种选择：使用setImageDrawable。第二件事是，似乎ImageAdapter每次滚动GridView时都会为ImageViews调用setImageResource方法，而不是在生成GridView时调用一次。您可以通过增加图像数组的范围来解决这个问题。在这种情况下，这很有效，因为GridView始终具有与mThumbIds数组定义的元素数相同的元素。

示例：

要让所有图像只生成一次，将Drawable数组添加到类中，并在构造期间填充它：

public class ImageAdapter extends BaseAdapter {

    private Context mContext;
    // Added drawable array:
    private Drawable[] mDrawables;

    public ImageAdapter(Context c) {

        mContext = c;

        // Fill in drawables with the images:
        for (int i = 0; i < mThumbIds.length; i++) {
        Bitmap bitmap = BitmapFactory.decodeResource(mContext.getResources(), mThumbIds[i]);
        mDrawables[i] = new BitmapDrawable(mContext.getResources(), bitmap);
        }
    } `

现在，您所要做的就是更改setImageDrawable的setImageResource并传递mDrawables数组的成员：

public View getView(int position, View convertView, ViewGroup parent) {

    ImageView imageView;
    if (convertView == null) {
        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;
    }

    // Changed to setImageDrawable:
    imageView.setImageDrawable(mDrawables[pposition]);
    return imageView;
}

结果是图像只会加载到Drawables中并存储一次，而setImageDrawable可以更快地访问这些图像，从而修复滚动。

如何在GridView中预加载所有图像？ - Android

1 个答案: