Bitmap缩放(二)

先得到位图宽高不用加载位图,然后按ImageView比例缩放,得到缩放的尺寸进行压缩并加载位图.inSampleSize是缩放多少倍,小于1默认是1,通过调节其inSampleSize参数，比如调节为2，宽高会为原来的1/2，内存变回原来的1/4.

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:id="@+id/line1"
    android:layout_height="match_parent"
    tools:context=".MainActivity">
<ImageView
    android:id="@+id/image"
    android:layout_width="match_parent"
    android:layout_height="300dp" />

</LinearLayout>

布局文件

public class MainActivity extends AppCompatActivity {

    @Override

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

        BitmapFactory.Options factoryOptions = new BitmapFactory.Options();
// 不将图片读取到内存中，仍然可以通过参数获得它的高宽
        factoryOptions.inJustDecodeBounds = true;
        BitmapFactory.decodeFile("/sdcard/AAAImage/image2.png", factoryOptions);
        int imageWidth = factoryOptions.outWidth;
        int imageHeight = factoryOptions.outHeight;

        ViewGroup.LayoutParams layoutParams = imageView.getLayoutParams();
        int width2 = layoutParams.width;
        int height2 = layoutParams.height;
        // 等比缩小，previewWidth和height是imageView的宽高
        int scaleFactor = Math.max(imageWidth /width2,
                imageHeight /height2);

// 将图片读取到内存中
        factoryOptions.inJustDecodeBounds = false;
// 设置等比缩小图
        factoryOptions.inSampleSize = scaleFactor;
// 样图可以回收内存
        factoryOptions.inPurgeable = true;
     Bitmap uploadImage = BitmapFactory
                .decodeFile("/sdcard/AAAImage/image2.png", factoryOptions);

        imageView.setImageBitmap(uploadImage);
//加载显示一符图像，对内存的使用有显著影响，BitmapFactory提供了一系列静态方法加载不同来源的图片。

    }

    }

位图缩放可以优化内存,面试必考

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