Android學習：圖片視圖（ImageView）

我們要將一張圖片顯示在螢幕上，首先需要建立一個顯示圖片的對象，在Android中，這個對象是ImageView對象，然後通過setImageResource

方法來設定要顯示的圖片資源索引。當然還可以對圖片執行一些其他的操作，比如設定它的Alpha值等。這裡將直接用一個樣本來分析ImageView的使

用，該樣本中通過一個線程來不斷更新Image的Alpha值。

MainActivity.java

package com.example.examples_04_15;import android.os.Bundle;import android.os.Handler;import android.os.Message;import android.app.Activity;import android.view.Menu;import android.widget.ImageView;import android.widget.TextView;public class MainActivity extends Activity {ImageView imageView;TextView textView;int image_alpha = 255;Handler mHandler = new Handler();boolean isrun = false;@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);isrun = true;imageView = (ImageView)findViewById(R.id.ImageView01);textView = (TextView)findViewById(R.id.TextView01);imageView.setImageResource(R.drawable.log);imageView.setAlpha(image_alpha);//開啟一個線程來讓Alpha值遞減new Thread(new Runnable() {@Overridepublic void run() {// TODO Auto-generated method stubwhile (isrun) {try {Thread.sleep(200);updateAlpha();} catch (InterruptedException e) {e.printStackTrace();}}}}).start();//接收訊息之後更新imageView視圖mHandler = new Handler() {@Overridepublic void handleMessage(Message msg) {// TODO Auto-generated method stubsuper.handleMessage(msg);imageView.setAlpha(image_alpha);textView.setText("現在alpha值是：" + Integer.toString(image_alpha));imageView.invalidate();}};}public void updateAlpha(){if (image_alpha - 7 >= 0) {image_alpha -= 7;}else{image_alpha = 0;isrun = false;}mHandler.sendMessage(mHandler.obtainMessage());}}

activity_main.xml

<RelativeLayout 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: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=".MainActivity" >    <ImageView         android:id="@+id/ImageView01"        android:layout_width="wrap_content"        android:layout_height="wrap_content"/>    <TextView        android:id="@+id/TextView01"        android:layout_below="@id/ImageView01"        android:layout_width="wrap_content"        android:layout_height="wrap_content"        /></RelativeLayout>