一般在android程序中把图片文件放在res/drawable目录下就可以通过R.drawable.id来使用,但在存储卡中的图片怎样引用呢?下面通过实现这个功能来介绍Bitmap的用法。
程序如下:
import java.io.File;
import android.app.Activity;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.ImageView;
import android.widget.TextView;
public class A10Activity extends Activity {
private Button b;
private ImageView iv;
private TextView tv;
private String fileName="sdcard/picture/红叶.jpg";
//private String fileName="sdcard/picture/红叶.jpg";这种写法是错误的,路径不是以
//设备开头
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
b=(Button)findViewById(R.id.button);
b.setOnClickListener(new OnClickListener(){
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
iv=(ImageView)findViewById(R.id.imageview);
tv=(TextView)findViewById(R.id.textview);
File f=new File(fileName);
//先判断图片文件是否存在
if(f.exists()){
//如果存在,通过Bitmap将图片放入ImageView中显示出来
/*BitmapFactory(Android.graphics.BitmapFactory)是Android API提供的对象,该对象
*的decodeFile()方法将手机中的图片文件转换成Bitmap对象。*/
Bitmap bm=BitmapFactory.decodeFile(fileName);
iv.setImageBitmap(bm);
tv.setText(fileName);
}
else{
tv.setText("文件不存在");
}
}
});
}
}
BitmapFactory也提供了其他方法,例如decodeResource()可以将res/drawable内预先存入的图片文件转换成Bitmap对象,decodeStream()方法可将InputStream转化成Bitmap对象。
下面这个例子是利用Matrix.setRotate()方法来实现ImageView的旋转。原理是将ImageView放入Bitmap中,然后利用Bitmap.createBitmap()方法来创建新的Bitmap对象,在创建的同时,Matrix对象里的setRotate()方法动态旋转新创建的Bitmap.然后将旋转好的Bitmap对象以新构造的方式创建新的Bitmap,并将其放入原来的ImageView中。
程序如下所示:
import android.app.Activity;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Matrix;
import android.graphics.drawable.BitmapDrawable;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.ImageView;
import android.widget.TextView;
public class A11Activity extends Activity {
private ImageView iv;
private TextView tv;
private Button left,right;
private int times;
private int angle;
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
times=1;
angle=1;
iv=(ImageView)findViewById(R.id.iv);
tv=(TextView)findViewById(R.id.tv);
left=(Button)findViewById(R.id.left);
left.setText("向左转");
right=(Button)findViewById(R.id.right);
right.setText("向右转");
final Bitmap bmp=BitmapFactory.decodeResource(getResources(), R.drawable.a); //自己引入一张图片a.png
final int width=bmp.getWidth();
final int height=bmp.getHeight();
iv.setImageBitmap(bmp);
left.setOnClickListener(new OnClickListener(){
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
angle--;
if(angle<-20){ //设置最多旋转20度
angle=-20;
}
int width01=width*times;
int height01=height*times;
float width02=(float)(width01/width);
float height02=(float)(width02/height);
Matrix m=new Matrix();
m.postScale(width02, height02);
m.setRotate(5*angle);
Bitmap bmp01=Bitmap.createBitmap(bmp, 0, 0, width, height, m, true);
BitmapDrawable bd=new BitmapDrawable(bmp01);
iv.setImageDrawable(bd);
tv.setText(Integer.toString(5*angle));
}
});
right.setOnClickListener(new OnClickListener(){
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
angle++;
if(angle>20){
angle=20;
}
int width01=width*times;
int height01=height*times;
float width02=(float)(width01/width);
float height02=(float)(width02/height);
Matrix m=new Matrix();
m.postScale(width02, height02);
m.setRotate(5*angle);
Bitmap bmp01=Bitmap.createBitmap(bmp, 0, 0, width, height, m, true);
BitmapDrawable bd=new BitmapDrawable(bmp01);
iv.setImageDrawable(bd);
tv.setText(Integer.toString(5*angle));
}
});
}
}
res/layout/main.xml如下:
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical" >
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="@string/hello" />