联网查看图片的Demo

刚刚学习完Android数据存储和访问做了一个联网查看图片的小案例。

效果图如下：

源码下载地址：https://coding.net/u/gxs1225/p/InternetImageView/git

注意：

因为需要联网，所以要在 AndroidManifest.xml 中加上联网的权限，不加会报错的呦！

<code class="hljs xml has-numbering"><span class="hljs-tag"><<span class="hljs-title">uses-permission</span> <span class="hljs-attribute">android:name</span>=<span class="hljs-value">"android.permission.INTERNET"</span>/></span></code><ul style="display: block;" class="pre-numbering"><li>1</li></ul>

为什么通过子线程加载图片？

分析： 由于网络连接需要很长的时间，才能返回页面的内容。如果此连接动作直接在主线程，也就是UI线程中处理，

整个程序处于很长的一个等待状态，这样造成用户体验不好，为了解决这个问题，必须把这个任务放置到单独线程中运行，即建一个子线程，避免阻塞UI线程，这样就不会对主线程有任何影。还加快了图片的加载速度。

步骤1

分析：

首先需要写一个布局文件，一个ImageView用于存放图片显示的位置，一个EditText用于填写图片的URL地址，一个Button按钮，用于事件处理。

代码如下：

<code class="hljs xml has-numbering"><span class="hljs-tag"><<span class="hljs-title">LinearLayout</span> <span class="hljs-attribute">xmlns:android</span>=<span class="hljs-value">"http://schemas.android.com/apk/res/android"</span>
<span class="hljs-attribute">xmlns:tools</span>=<span class="hljs-value">"http://schemas.android.com/tools"</span>
<span class="hljs-attribute">android:layout_width</span>=<span class="hljs-value">"match_parent"</span>
<span class="hljs-attribute">android:layout_height</span>=<span class="hljs-value">"match_parent"</span>
<span class="hljs-attribute">android:orientation</span>=<span class="hljs-value">"vertical"</span>
<span class="hljs-attribute">android:paddingBottom</span>=<span class="hljs-value">"@dimen/activity_vertical_margin"</span>
<span class="hljs-attribute">android:paddingLeft</span>=<span class="hljs-value">"@dimen/activity_horizontal_margin"</span>
<span class="hljs-attribute">android:paddingRight</span>=<span class="hljs-value">"@dimen/activity_horizontal_margin"</span>
<span class="hljs-attribute">android:paddingTop</span>=<span class="hljs-value">"@dimen/activity_vertical_margin"</span>
<span class="hljs-attribute">tools:context</span>=<span class="hljs-value">".MainActivity"</span> ></span>

<span class="hljs-tag"><<span class="hljs-title">ImageView
</span>        <span class="hljs-attribute">android:id</span>=<span class="hljs-value">"@+id/ivImage"</span>
<span class="hljs-attribute">android:layout_width</span>=<span class="hljs-value">"match_parent"</span>
<span class="hljs-attribute">android:layout_height</span>=<span class="hljs-value">"wrap_content"</span>
<span class="hljs-attribute">android:layout_gravity</span>=<span class="hljs-value">"center"</span>
<span class="hljs-attribute">android:layout_weight</span>=<span class="hljs-value">"1"</span> /></span>

<span class="hljs-tag"><<span class="hljs-title">EditText
</span>        <span class="hljs-attribute">android:id</span>=<span class="hljs-value">"@+id/etImageUrl"</span>
<span class="hljs-attribute">android:layout_width</span>=<span class="hljs-value">"match_parent"</span>
<span class="hljs-attribute">android:layout_height</span>=<span class="hljs-value">"wrap_content"</span>
<span class="hljs-attribute">android:ems</span>=<span class="hljs-value">"10"</span>
<span class="hljs-attribute">android:hint</span>=<span class="hljs-value">"请输入图片的地址"</span>
<span class="hljs-attribute">android:text</span>=<span class="hljs-value">"http://avatar.csdn.net/C/9/A/1_yf210yf.jpg"</span> /></span>

<span class="hljs-tag"><<span class="hljs-title">Button
</span>        <span class="hljs-attribute">android:id</span>=<span class="hljs-value">"@+id/btnView"</span>
<span class="hljs-attribute">android:layout_width</span>=<span class="hljs-value">"wrap_content"</span>
<span class="hljs-attribute">android:layout_height</span>=<span class="hljs-value">"wrap_content"</span>
<span class="hljs-attribute">android:layout_gravity</span>=<span class="hljs-value">"center"</span>
<span class="hljs-attribute">android:background</span>=<span class="hljs-value">"@drawable/button_bg"</span>
<span class="hljs-attribute">android:onClick</span>=<span class="hljs-value">"viewImage"</span>
<span class="hljs-attribute">android:text</span>=<span class="hljs-value">"浏览"</span> /></span>

<span class="hljs-tag"></<span class="hljs-title">LinearLayout</span>></span></code>

步骤2

分析：

在MainActivity.java中创建一个子线程，通过这个子线程来获取图片。

当一个程序第一次启动时，Android会同时启动一个对应的主线程(Main

Thread)，主线程主要负责处理与UI相关的事件。子线程不能单独处理获UI相关的事件

，那么必须借助Handler来更新界面。为此，在界面

Activity中创建一个Handler对象，并在handleMessage()中更新UI。 MainActivity.java

<code class="hljs java has-numbering"><span class="hljs-keyword">package</span> com.bzu.gxs;
<span class="hljs-keyword">import</span> java.io.IOException;
<span class="hljs-keyword">import</span> java.io.InputStream;
<span class="hljs-keyword">import</span> java.net.HttpURLConnection;
<span class="hljs-keyword">import</span> java.net.MalformedURLException;
<span class="hljs-keyword">import</span> java.net.URL;
<span class="hljs-keyword">import</span> android.os.Bundle;
<span class="hljs-keyword">import</span> android.os.Handler;
<span class="hljs-keyword">import</span> android.os.Message;
<span class="hljs-keyword">import</span> android.app.Activity;
<span class="hljs-keyword">import</span> android.graphics.Bitmap;
<span class="hljs-keyword">import</span> android.graphics.BitmapFactory;
<span class="hljs-keyword">import</span> android.text.TextUtils;
<span class="hljs-keyword">import</span> android.view.Menu;
<span class="hljs-keyword">import</span> android.view.View;
<span class="hljs-keyword">import</span> android.widget.EditText;
<span class="hljs-keyword">import</span> android.widget.ImageView;
<span class="hljs-keyword">import</span> android.widget.Toast;
<span class="hljs-keyword">public</span> <span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">MainActivity</span> <span class="hljs-keyword">extends</span> <span class="hljs-title">Activity</span> {</span>
<span class="hljs-keyword">private</span> EditText etImageUrl;
<span class="hljs-keyword">private</span> ImageView ivImage;
<span class="hljs-keyword">public</span> <span class="hljs-keyword">static</span> <span class="hljs-keyword">final</span> <span class="hljs-keyword">int</span> SHOWIMAGE=<span class="hljs-number">1</span>;
<span class="hljs-keyword">public</span> <span class="hljs-keyword">static</span> <span class="hljs-keyword">final</span> <span class="hljs-keyword">int</span> SHOWFAIL=<span class="hljs-number">0</span>;
<span class="hljs-comment">// Handler 处理事件</span>
<span class="hljs-keyword">private</span> Handler handler=<span class="hljs-keyword">new</span> Handler(){
<span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title">handleMessage</span>(android.os.Message msg) {
<span class="hljs-keyword">switch</span> (msg.what) {
<span class="hljs-keyword">case</span> SHOWIMAGE:
Bitmap bitmap=(Bitmap) msg.obj;
ivImage.setImageBitmap(bitmap);
<span class="hljs-keyword">break</span>;

<span class="hljs-keyword">case</span> SHOWFAIL:
ivImage.setImageResource(R.drawable.button_bg);
Toast.makeText(MainActivity.<span class="hljs-keyword">this</span>, <span class="hljs-string">"显示图片失败"</span>, Toast.LENGTH_LONG).show();
<span class="hljs-keyword">break</span>;

<span class="hljs-keyword">default</span>:
<span class="hljs-keyword">break</span>;
}
};
};
<span class="hljs-annotation">@Override</span>
<span class="hljs-keyword">protected</span> <span class="hljs-keyword">void</span> <span class="hljs-title">onCreate</span>(Bundle savedInstanceState) {
<span class="hljs-keyword">super</span>.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
initViews();
ivImage.setImageResource(R.drawable.button_bg);
}
<span class="hljs-comment">// 查找的ID</span>
<span class="hljs-keyword">private</span> <span class="hljs-keyword">void</span> <span class="hljs-title">initViews</span>() {
etImageUrl=(EditText) findViewById(R.id.etImageUrl);
ivImage=(ImageView) findViewById(R.id.ivImage);
}

<span class="hljs-comment">// 按钮点击事件</span>
<span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title">viewImage</span>(View view){
<span class="hljs-keyword">final</span> String imageUrl=etImageUrl.getText().toString();
<span class="hljs-keyword">if</span>(TextUtils.isEmpty(imageUrl)){
Toast.makeText(<span class="hljs-keyword">this</span>, <span class="hljs-string">"图片路径不能为空"</span>, Toast.LENGTH_LONG).show();
}<span class="hljs-keyword">else</span>{
<span class="hljs-keyword">new</span> Thread(){
<span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title">run</span>() {
<span class="hljs-keyword">try</span> {
URL url=<span class="hljs-keyword">new</span> URL(imageUrl);
HttpURLConnection httpURLConnection=(HttpURLConnection) url.openConnection();
httpURLConnection.setRequestMethod(<span class="hljs-string">"GET"</span>);
httpURLConnection.setConnectTimeout(<span class="hljs-number">5000</span>);
<span class="hljs-keyword">int</span> responseCode=httpURLConnection.getResponseCode();
<span class="hljs-keyword">if</span>(responseCode==<span class="hljs-number">200</span>){
InputStream inputStream=httpURLConnection.getInputStream();
Bitmap bitmap=BitmapFactory.decodeStream(inputStream);
Message message=<span class="hljs-keyword">new</span> Message();
message.what=SHOWIMAGE;
message.obj=bitmap;
<span class="hljs-comment">//ivImage.setImageBitmap(bitmap);</span>
handler.sendMessage(message);
}<span class="hljs-keyword">else</span>{
Message message=<span class="hljs-keyword">new</span> Message();
message.what=SHOWFAIL;
handler.sendMessage(message);
}
} <span class="hljs-keyword">catch</span> (MalformedURLException e) {
e.printStackTrace();
} <span class="hljs-keyword">catch</span> (IOException e) {
e.printStackTrace();
}
}
}.start();
}
}
}
</code>