图片的旋转

   主要运用了Matrix类，postRotate()方法和postScale()方法；

   Matrix：中文是矩阵的意思，主要用于图片的缩放，平移与旋转；

   postRotate()用于旋转，postScale()用于缩放；

具体MianAvtivity代码如下：

package com.example.lenovo.a1105;

import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Matrix;
import android.graphics.drawable.BitmapDrawable;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;
import android.widget.ImageView;

public class MainActivity extends AppCompatActivity {

    private Bitmap myBitmap;
    private Matrix myMatrix=new Matrix();
    private int width;
    private int height;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        Button rotaToLeft=(Button)findViewById(R.id.rotaToLeft);
        Button rotaToRight=(Button)findViewById(R.id.rotaToRight);
        Button scaleBig=(Button)findViewById(R.id.scaleBig);
        Button scaleSmall=(Button)findViewById(R.id.scaleSmall);

        myBitmap= BitmapFactory.decodeResource(getResources(),R.drawable.pic);
                                     //获取资源图片pic的Bitmap
        width=myBitmap.getWidth();
        height=myBitmap.getHeight();
                            //这两句是获取图片原始大小

        //以下是四个按钮的单击事件

        rotaToLeft.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                myMatrix.postRotate(-90);  //逆时针旋转90°

                Bitmap newBitmap=Bitmap.createBitmap(myBitmap,0,0,width,height,myMatrix,false);
                                //创建一个新的图片，重新绘图
                BitmapDrawable newBmp=new BitmapDrawable(newBitmap);
                               //把Bitmap装换成Drawable，使其可以显示在ImageView与ImageButton中
                ImageView imageView=(ImageView)findViewById(R.id.pic);
                               //创建Image对象
                imageView.setImageDrawable(newBmp);
            }
        });
        rotaToRight.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                myMatrix.postRotate(90); //顺时针旋转90°
                Bitmap newBitmap=Bitmap.createBitmap(myBitmap,0,0,width,height,myMatrix,false);
                BitmapDrawable newBmp=new BitmapDrawable(newBitmap);
                ImageView imageView=(ImageView)findViewById(R.id.pic);
                imageView.setImageDrawable(newBmp);
            }
        });
        scaleBig.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                myMatrix.postScale(1.2f, 1.2f);

                Bitmap newBitmap=Bitmap.createBitmap(myBitmap,0,0,width,height,myMatrix,true);
                BitmapDrawable newBmp=new BitmapDrawable(newBitmap);
                ImageView imageView=(ImageView)findViewById(R.id.pic);
                imageView.setImageDrawable(newBmp);

            }
        });
        scaleSmall.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                myMatrix.postScale(0.5f, 0.5f);

                Bitmap newBitmap=Bitmap.createBitmap(myBitmap,0,0,width,height,myMatrix,true);
                BitmapDrawable newBmp=new BitmapDrawable(newBitmap);
                ImageView imageView=(ImageView)findViewById(R.id.pic);
                imageView.setImageDrawable(newBmp);
            }
        });
    }

}

main.xml代码如下：

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">

    <ImageView
        android:id="@+id/pic"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center"
        android:background="@drawable/pic"
        android:layout_marginTop="40dp"
        />

    <LinearLayout
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="40dp"
        android:orientation="horizontal">
        <Button
            android:id="@+id/rotaToLeft"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="左旋" />
        <Button
            android:id="@+id/rotaToRight"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="右旋" />

        <Button
            android:id="@+id/scaleBig"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="放大" />

        <Button
            android:id="@+id/scaleSmall"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="缩小" />


    </LinearLayout>


</LinearLayout>

实现后如下：