Android上在两个Activity之间传递Bitmap对象
因为我做Android应用的时间不长，所以当我第一次在android之间传递Bitmap对象的时候我直接用了Intent.putExtra的方法实现了，当时我选择的是一张图像的ROI区域，所以工作的很好，但是当我尝试将整个图片做为Bitmap对象传到另外一个Activity中的时候总是得到一个错误fatal bind error我当时很郁闷了好久，后来google才发现是这样传递Bitmap对象的方式不对，Activity之间传递Bitmap有大小限制，而且这个大小限制很小，512x512的图片肯定会得到我上述的这个错误，于是我想到了先保存到SD卡上然后传递路径的方法，但是SD卡属于外部存储，可能不是特别方便，后来看到有人通过内部存储方式实现了在两个Activity之间传递Bitmap对象以及其它支持串行化的Java对象，我觉得很好，所以就写了这篇博客。关键点有如下：
1． HTTP客户端下载图片，通过ImageView对象显示
2． 把ImageView上的Bitmap对象从当前Activity传递到另外一个
Activity中并显示出来
3． 基于串行化传递Java对象数据
首先看我是怎么实现HTTP客户端下载图片，通过异步Task接口实现HTTP客户端下载图片并通过Handler来更新ImageView，代码如下：
package com.example.sharedemo; import java.io.IOException; import java.io.InputStream; import org.apache.http.HttpEntity; import org.apache.http.HttpResponse; import org.apache.http.HttpStatus; import org.apache.http.client.ClientProtocolException; import org.apache.http.client.HttpClient; import org.apache.http.client.methods.HttpGet; import org.apache.http.impl.client.DefaultHttpClient; import android.graphics.Bitmap; import android.graphics.BitmapFactory; import android.os.AsyncTask; import android.os.Handler; import android.os.Message; import android.util.Log; public class ImageLoadTask extends AsyncTask<String, Void, Bitmap> { private Handler handler; public ImageLoadTask(Handler handler) { this.handler = handler; } protected void onPostExecute(Bitmap bitmap) { Message msg = new Message(); msg.obj = bitmap; handler.sendMessage(msg); } @Override protected Bitmap doInBackground(String... urls) { Bitmap bitmap = null; // create HTTP client HttpClient httpclient = new DefaultHttpClient(); try { // GET request Log.i("image-url", urls[0]); HttpGet httpRequest = new HttpGet(urls[0]); HttpResponse httpResponse = httpclient.execute(httpRequest); if (httpResponse.getStatusLine().getStatusCode() == HttpStatus.SC_OK) { // get entity from response HttpEntity httpEntity = httpResponse.getEntity(); // read stream InputStream is = httpEntity.getContent(); bitmap = BitmapFactory.decodeStream(is); is.close(); Log.i("image", "already get the image by url : " + urls[0]); } } catch (ClientProtocolException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } finally { httpclient.getConnectionManager().shutdown(); } return bitmap; } }
在当前的Activity中通过按钮上的事件响应实现切换View到对应的Activity中去，同时实现Java串行化数据传递。MainActivity的代码如下：
package com.example.sharedemo; import java.io.ByteArrayOutputStream; import java.io.FileOutputStream; import android.app.Activity; import android.content.Context; import android.content.Intent; import android.graphics.Bitmap; import android.graphics.Matrix; import android.graphics.drawable.BitmapDrawable; import android.os.Bundle; import android.os.Handler; import android.os.Message; import android.util.Log; import android.view.View; import android.view.View.OnClickListener; import android.widget.Button; import android.widget.ImageView; public class MainActivity extends Activity implements OnClickListener{ public final static String SHARE_BITMAP_COMMAND = "share-image"; public final static String SHARE_TEXT_DATA_COMMAND = "share-text-data"; private Handler handler; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); setupOnClickListener(); } private void setupOnClickListener() { Button bitmapBtn = (Button)this.findViewById(R.id.bitmapShareBtn); bitmapBtn.setTag(SHARE_BITMAP_COMMAND); bitmapBtn.setOnClickListener(this); Button textDataBtn = (Button)this.findViewById(R.id.mapShareBtn); textDataBtn.setTag(SHARE_TEXT_DATA_COMMAND); textDataBtn.setOnClickListener(this); final ImageView imageView = (ImageView)this.findViewById(R.id.imageView1); handler = new Handler() { public void handleMessage(Message msg) { Bitmap bitmap = (Bitmap)msg.obj; if(bitmap != null) { /* // 为防止原始图片过大导致内存溢出，这里先缩小原图显示，然后释放原始Bitmap占用的内存 Bitmap smallBitmap = zoomBitmap(bitmap, bitmap.getWidth()/ 5, bitmap.getHeight() / 5); // 释放资源 bitmap.recycle(); // 显示图片 imageView.setImageBitmap(smallBitmap); imageView.invalidate(); */ imageView.setImageBitmap(bitmap); } } }; ImageLoadTask task = new ImageLoadTask(handler); task.execute("https://img-blog.csdn.net/20150607143208238"); } public static Bitmap zoomBitmap(Bitmap bitmap, int width, int height) { int w = bitmap.getWidth(); int h = bitmap.getHeight(); Matrix matrix = new Matrix(); float scaleWidth = ((float) width / w); float scaleHeight = ((float) height / h); matrix.postScale(scaleWidth, scaleHeight); // 不改变原来图像大小 Bitmap newbmp = Bitmap.createBitmap(bitmap, 0, 0, w, h, matrix, true); return newbmp; } @Override public void onClick(View v) { Object tag = v.getTag(); Log.i("command", tag.toString()); if(SHARE_BITMAP_COMMAND.equals(tag)) { Intent intent = new Intent(this.getApplicationContext(), ImageProcessActivity.class); ImageView imageView = (ImageView)this.findViewById(R.id.imageView1); Bitmap bitmap = ((BitmapDrawable)imageView.getDrawable()).getBitmap(); intent.putExtra("selectedImage", bitmap); intent.putExtra("name", "lena"); intent.putExtra("description", "超级大美女"); this.startActivity(intent); } else if(SHARE_TEXT_DATA_COMMAND.equals(tag)) { Intent intent = new Intent(this.getApplicationContext(), ImageProcessActivity.class); ImageView imageView = (ImageView)this.findViewById(R.id.imageView1); Bitmap bitmap = ((BitmapDrawable)imageView.getDrawable()).getBitmap(); // save it first then pass URI ImageInfoBean dto = new ImageInfoBean(); String uri = createImageFromBitmap(bitmap); dto.setDescription("超级大美女"); dto.setName("lena"); dto.setUri(uri); intent.putExtra("tiger", dto); this.startActivity(intent); } } public String createImageFromBitmap(Bitmap bitmap) { String fileName = "myImage"; try { ByteArrayOutputStream bytes = new ByteArrayOutputStream(); bitmap.compress(Bitmap.CompressFormat.JPEG, 100, bytes); FileOutputStream fo = openFileOutput(fileName, Context.MODE_PRIVATE); fo.write(bytes.toByteArray()); fo.close(); } catch (Exception e) { e.printStackTrace(); fileName = null; } Log.i("fileName", fileName); return fileName; } }
对应另外一个Activity中实现读取与组装Bitmap对象显示的代码如下：
package com.example.sharedemo; import java.io.FileNotFoundException; import android.app.Activity; import android.graphics.Bitmap; import android.graphics.BitmapFactory; import android.os.Bundle; import android.widget.ImageView; import android.widget.TextView; public class ImageProcessActivity extends Activity { @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.share_info); backFillData(); } private void backFillData() { Object obj = this.getIntent().getExtras().get("tiger"); ImageView imageView = (ImageView)this.findViewById(R.id.imageView1); TextView text1 = (TextView)this.findViewById(R.id.textView1); TextView text2 = (TextView)this.findViewById(R.id.textView2); try { if(obj != null && obj instanceof ImageInfoBean) { ImageInfoBean dto = (ImageInfoBean)obj; Bitmap bitmap = BitmapFactory.decodeStream(this.openFileInput(dto.getUri())); imageView.setImageBitmap(bitmap); imageView.invalidate(); // refresh text1.setText("名称: " + dto.getName()); text2.setText("描述: " + dto.getDescription()); return; } } catch (FileNotFoundException e) { e.printStackTrace(); } Bitmap bitmap = (Bitmap) this.getIntent().getParcelableExtra("selectedImage"); String name = this.getIntent().getExtras().getString("name"); String description = this.getIntent().getExtras().getString("description"); if(bitmap != null) { imageView.setImageBitmap(bitmap); imageView.invalidate(); // refresh } if(name != null) { text1.setText("名称: " + name); } if(description != null) { text2.setText("描述: " + description); } } }
对应的Java串行化对象类代码如下：
package com.example.sharedemo; import java.io.Serializable; public class ImageInfoBean implements Serializable { /** * */ private static final long serialVersionUID = 1L; public String getName() { return name; } public void setName(String name) { this.name = name; } public String getDescription() { return description; } public void setDescription(String description) { this.description = description; } public String getUri() { return uri; } public void setUri(String uri) { this.uri = uri; } private String name; private String description; private String uri; }
最后声明：
别忘记在Manifest文件添加网络访问的权限
<uses-permission android:name="android.permission.INTERNET"/>
第一个按钮【传递图片】将会演示我遇到错误，第二按钮【传递文本数据】
将会演示正确的处理结果，显示如下：
