public class MainActivity extends AppCompatActivity {
private Button addAlpha;
private Button downAlpha;
private Button next;
private ImageView imageView1;
int [] images = new int []{ //用数组存储春,夏,秋,冬四张图片
R.drawable.spring,
R.drawable.summer,
R.drawable.fall,
R.drawable.winter
} ;
int currentImage = 0 ; //定义当前默认显示的图片
int alpha = 255 ; //定义图片起始透明度
@Override
protected void onCreate(Bundle savedInstanceState) {
super .onCreate(savedInstanceState);
setContentView(R.layout.activity_imageview);
addAlpha = (Button) findViewById(R.id.addAlpha);
downAlpha = (Button) findViewById(R.id.downAlpha);
next = (Button) findViewById(R.id.next);
imageView1 = (ImageView) findViewById(R.id.imageView1);
//对增加图片透明度按钮设置监听事件
addAlpha.setOnClickListener( new View.OnClickListener() {
@TargetApi (Build.VERSION_CODES.JELLY_BEAN)
@Override
public void onClick(View v) {
if (alpha >= 255 ){ //255是透明度上线
alpha = 255 ;
}
else { //每点击增加透明度按钮,透明度增加20
alpha += 20 ;
}
imageView1.setImageAlpha(alpha); //为图片设置透明度
}
});
//对减少透明度按钮设置监听事件
downAlpha.setOnClickListener( new View.OnClickListener() {
@TargetApi (Build.VERSION_CODES.JELLY_BEAN)
@Override
public void onClick(View v) {
if (alpha <= 0 ){ //透明度下限
alpha = 0 ;
}
else {
alpha -= 20 ;
}
imageView1.setImageAlpha(alpha); //为图片设置透明度
}
});
//对切换图片按钮设置监听事件
next.setOnClickListener( new View.OnClickListener() {
@Override
public void onClick(View v) {
//控制显示下一张图片
imageView1.setImageResource(images[++ currentImage % images.length]);
}
});
}
}
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