你的位置:首页 > 操作系统

[操作系统]Android 加载大图片到内存


本文演示android中图片加载到内存

首先设计界面:

代码如下:

<LinearLayout ="http://schemas.android.com/apk/res/android"  ="http://schemas.android.com/tools"  android:layout_width="match_parent"  android:layout_height="match_parent"  android:orientation="vertical"  tools:context=".MainActivity" >  <Button    android:layout_width="wrap_content"    android:layout_height="wrap_content"    android:onClick="load"    android:text="加载图片到内存" />  <ImageView    android:id="@+id/iv"    android:layout_width="fill_parent"    android:layout_height="fill_parent" /></LinearLayout>

往mnt/sdcard中上传测试图片

添加逻辑部分代码:

public class MainActivity extends Activity {  private ImageView iv;  @Override  protected void onCreate(Bundle savedInstanceState) {    super.onCreate(savedInstanceState);    setContentView(R.layout.activity_main);    iv = (ImageView) findViewById(R.id.iv);  }  public void load() {    Bitmap bitmap = BitmapFactory.decodeFile("/sdcard/a.jpg");    iv.setImageBitmap(bitmap);  }}

运行代码,产生错误,原因是图片太大(选取的是大照片)

可以使用BitmapFactory中包含的静态类Options在不解析图片信息的前提下得到图片的宽高信息:

  BitmapFactory.Options opts = new Options();    // 不去解析图片信息,只是得到图片的头部信息 宽高    opts.inJustDecodeBounds = true;    BitmapFactory.decodeFile("/sdcard/a.jpg", opts);    int imageHeight = opts.outHeight;    int imagewidth = opts.outWidth;    System.out.println("图片宽:" + imagewidth);    System.out.println("图片高" + imageHeight);

 

运行一下:

09-04 06:09:10.519: I/System.out(1812): 图片宽:2560
09-04 06:09:10.519: I/System.out(1812): 图片高1920

接下来得到手机屏幕的宽高:

    //得到手机屏幕的宽高    WindowManager wm = (WindowManager)getSystemService(WINDOW_SERVICE);    int height = wm.getDefaultDisplay().getHeight();    int width = wm.getDefaultDisplay().getWidth();

可以看到getHeight与getWidth方法均已过时,使用下面的方法替代:

    // 得到手机屏幕的宽高    WindowManager wm = (WindowManager) getSystemService(WINDOW_SERVICE);    Point outSize = new Point();    wm.getDefaultDisplay().getSize(outSize); // 3.0以后的版本才能使用

完整代码如下:

package com.wuyudong.loadimage;import android.os.Bundle;import android.annotation.SuppressLint;import android.app.Activity;import android.graphics.Bitmap;import android.graphics.BitmapFactory;import android.graphics.BitmapFactory.Options;import android.graphics.Point;import android.view.Menu;import android.view.View;import android.view.WindowManager;import android.widget.ImageView;public class MainActivity extends Activity {  private ImageView iv;  private int windowHeight;  private int windowWidth;  protected void onCreate(Bundle savedInstanceState) {    super.onCreate(savedInstanceState);    setContentView(R.layout.activity_main);    iv = (ImageView) findViewById(R.id.iv);    // 得到手机屏幕的宽高    WindowManager wm = (WindowManager) getSystemService(WINDOW_SERVICE);    windowHeight = wm.getDefaultDisplay().getHeight();    windowWidth = wm.getDefaultDisplay().getWidth();        //Point outSize = new Point();    //wm.getDefaultDisplay().getSize(outSize); // 3.0以后的版本才能使用    //windowHeight = outSize.y;    //windowWidth = outSize.x;  }  public void load(View view) {    // Bitmap bitmap = BitmapFactory.decodeFile("/sdcard/a.jpg");    // iv.setImageBitmap(bitmap);    // 图片解析的配置    BitmapFactory.Options opts = new Options();    // 不去解析图片信息,只是得到图片的头部信息 宽高    opts.inJustDecodeBounds = true;    BitmapFactory.decodeFile("/sdcard/a.jpg", opts);    int imageHeight = opts.outHeight;    int imagewidth = opts.outWidth;    System.out.println("图片宽:" + imagewidth);    System.out.println("图片高" + imageHeight);    // 计算缩放比例    int scaleX = imagewidth / windowWidth;    int scaleY = imageHeight / windowHeight;    int scale = 1;    if (scaleX > scaleY & scaleY >= 1) {      scale = scaleX;    }    if (scaleY > scaleX & scaleX >= 1) {      scale = scaleY;    }    //解析图片    opts.inJustDecodeBounds = false;        //采样率    opts.inSampleSize = scale;    Bitmap bitmap = BitmapFactory.decodeFile("/sdcard/a.jpg", opts);    iv.setImageBitmap(bitmap);  }}