Android ImageView控件和SeekBar的问题

l2190215487 2016-07-31 04:03:43

通过SeekBar控件改变图片的透明度，并用Toast随时图片的透明度，然后发现不管怎么调SeekBar，图片的透明度都始终是1.0，这让我很费解，大神们指导下。。
这是java代码：
package com.example.application.seekbar;

import android.media.Image;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.ImageView;
import android.widget.SeekBar;
import android.widget.TextView;
import android.widget.Toast;

public class MainActivity extends AppCompatActivity {

Toast toast;
SeekBar seekBar;
ImageView imageView;
Float f;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);

seekBar = (SeekBar)findViewById(R.id.seekbar1);
imageView = (ImageView)findViewById(R.id.imageview1);
f = imageView.getAlpha();
toast=Toast.makeText(getApplicationContext(), f.toString(), Toast.LENGTH_SHORT);
seekBar.setOnSeekBarChangeListener(new SeekBar.OnSeekBarChangeListener() {
@Override
public void onProgressChanged(SeekBar seekBar, int progress, boolean fromUser) {
imageView.setImageAlpha(progress);
f = imageView.getAlpha();
toast=Toast.makeText(getApplicationContext(), f.toString(), Toast.LENGTH_SHORT);
toast.show();
}

@Override
public void onStartTrackingTouch(SeekBar seekBar) {

}

@Override
public void onStopTrackingTouch(SeekBar seekBar) {

}
});
}
}

这是xml代码：
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context="com.example.application.seekbar.MainActivity">

<ImageView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="@+id/imageview1"
android:src="@drawable/hello3"/>
<SeekBar
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:id="@+id/seekbar1"
android:max="200"
android:progress="100"/>
</LinearLayout>

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