解决Android BitmapFactory的基本使用问题

问题描述

使用方法bitmapfactory.decodefile转化bitmap时报错：java.lang.runtimeexception: canvas: trying to draw too large(120422400bytes) bitmap.

解决方案

报错原因：图片转化为bitmap超过最大值max_bitmap_size

frameworks/base/graphics/java/android/graphics/recordingcanvas.java

public static final int max_bitmap_size = 100 * 1024 * 1024; // 100 mb

/** @hide */
@override
protected void throwifcannotdraw(bitmap bitmap) {
    super.throwifcannotdraw(bitmap);
    int bitmapsize = bitmap.getbytecount();
    if (bitmapsize > max_bitmap_size) {
        throw new runtimeexception(
                "canvas: trying to draw too large(" + bitmapsize + "bytes) bitmap.");
    }
}

修改如下

//修改前
bitmap image = bitmapfactory.decodefile(filepath);
imageview.setimagebitmap(image);

//修改后
import android.graphics.bitmap;
import android.graphics.bitmapfactory;
import android.util.displaymetrics;

file file = new file(filepath);
if (file.exists() && file.length() > 0) {
    //获取设备屏幕大小
    displaymetrics dm = getresources().getdisplaymetrics();
    int screenwidth = dm.widthpixels;
    int screenheight = dm.heightpixels;
    //获取图片宽高
    bitmapfactory.options options = new bitmapfactory.options();
    options.injustdecodebounds = true;	
    bitmapfactory.decodefile(filepath, options);	
    float srcwidth = options.outwidth;	
    float srcheight = options.outheight;	
    //计算缩放比例
    int insamplesize = 1;	
    if (srcheight > screenheight || srcwidth > screenwidth) {	
        if (srcwidth > srcheight) {	
            insamplesize = math.round(srcheight / screenheight);	
        } else {	
            insamplesize = math.round(srcwidth / screenwidth);	
        }	
    }	
    options.injustdecodebounds = false;	
    options.insamplesize = insamplesize;	
    
    bitmap bitmap = bitmapfactory.decodefile(filepath, options);	
    imageview.setimagebitmap(bitmap);
}

相关参考：

android 图片缓存之 bitmap 详解
https://juejin.cn/post/6844903442939412493

bitmapfactory
https://developer.android.com/reference/android/graphics/bitmapfactory.html

bitmapfactory.options
bitmapfactory.options类是bitmapfactory对图片进行解码时使用的一个配置参数类，其中定义了一系列的public成员变量，每个成员变量代表一个配置参数。
https://blog.csdn.net/showdy/article/details/54378637

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