Bitmap 小例子

最新推荐文章于 2023-04-28 09:22:47 发布

原创最新推荐文章于 2023-04-28 09:22:47 发布 · 366 阅读

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本文介绍了一个Android应用中实现图片加载的方法，通过自定义BitmapFactory.Options来控制图片的解码过程，实现按需加载和内存优化，适用于移动端开发。

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<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    android:orientation="vertical"
    tools:context="com.moliying.a59_bitmaps.MainActivity">

    <Button
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="加载图片"
        android:onClick="loadImageClick"/>
    <ImageView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:src="@mipmap/ic_launcher"
        android:id="@+id/imageView"
        android:layout_gravity="center_horizontal" />
</LinearLayout>

package com.moliying.a59_bitmaps;

import android.content.Context;
import android.content.res.Resources;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.ImageView;

public class MainActivity extends AppCompatActivity {

    private  ImageView imageView;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        imageView = (ImageView) findViewById(R.id.imageView);
    }

    public void loadImageClick(View view){
        Bitmap b = loadImageFromResource(this,R.mipmap.zw2,100,100);
        imageView.setImageBitmap(b);
    }

    //加载图片
    private Bitmap loadImageFromResource(Context context,int resId, int reqWidth, int reqHeight) {
        //创建一个图片解码设置选项对象
        BitmapFactory.Options options = new BitmapFactory.Options();
        options.inJustDecodeBounds = true;//设置只解码图片的边界
        BitmapFactory.decodeResource(context.getResources(),resId,options);//解码图片
        options.inSampleSize = calculateSampleSize(options,reqWidth,reqHeight);
        options.inJustDecodeBounds = false;//设置为需要解码图片
        Bitmap b = BitmapFactory.decodeResource(getResources(),R.mipmap.zw2,options);
        return b;
    }

    //计算采样比例
    private int calculateSampleSize(BitmapFactory.Options options,int reqWidth,int reqHeight){
        BitmapFactory.Options opt = options;
        int width = opt.outWidth;
        int height = opt.outHeight;
        int inSampleSize = 1;
        if(width>reqWidth || height>reqHeight){
            if(width>height){
                inSampleSize = Math.round((float)height / (float) reqHeight);
            }else{
                inSampleSize = Math.round((float)width / (float) reqWidth);
            }
        }
        return inSampleSize;
    }
}