1page.title=Controlling the Camera 2parent.title=Capturing Photos 3parent.link=index.html 4 5trainingnavtop=true 6previous.title=Recording Videos Simply 7previous.link=videobasics.html 8 9@jd:body 10 11 12<div id="tb-wrapper"> 13 <div id="tb"> 14 15 <h2>This lesson teaches you to</h2> 16 <ol> 17 <li><a href="#TaskOpenCamera">Open the Camera Object</a></li> 18 <li><a href="#camera-preview">Create the Camera Preview</a></li> 19 <li><a href="#TaskSettings">Modify Camera Settings</a></li> 20 <li><a href="#TaskOrientation">Set the Preview Orientation</a></li> 21 <li><a href="#TaskTakePicture">Take a Picture</a></li> 22 <li><a href="#TaskRestartPreview">Restart the Preview</a></li> 23 <li><a href="#TaskReleaseCamera">Stop the Preview and Release the Camera</a></li> 24 </ol> 25 26 <h2>You should also read</h2> 27 <ul> 28 <li><a href="{@docRoot}guide/topics/media/camera.html#custom-camera">Building 29 a Camera App</a></li> 30 </ul> 31 </div> 32</div> 33 34<p>In this lesson, we discuss how to control the camera hardware directly using 35the framework APIs.</p> 36 37<p>Directly controlling a device camera requires a lot more code than requesting pictures or videos 38from existing camera applications. However, if you want to build a specialized camera application 39or something fully integrated in your app UI, this lesson shows you how.</p> 40 41 42<h2 id="TaskOpenCamera">Open the Camera Object</h2> 43 44<p>Getting an instance of the {@link android.hardware.Camera} object is the first step in the 45process of directly controlling the camera. As Android's own Camera application does, the 46recommended way to access the camera is to open {@link android.hardware.Camera} on a separate thread 47that's launched from {@link android.app.Activity#onCreate onCreate()}. This approach is a good idea 48since it can take a while and might bog down the UI thread. In a more basic implementation, 49opening the camera can be deferred to the {@link 50android.app.Activity#onResume onResume()} method to facilitate code reuse and keep the flow of 51control simple.</p> 52 53<p>Calling {@link android.hardware.Camera#open Camera.open()} throws an 54exception if the camera is already in use by another application, so we wrap it 55in a {@code try} block.</p> 56 57<pre> 58private boolean safeCameraOpen(int id) { 59 boolean qOpened = false; 60 61 try { 62 releaseCameraAndPreview(); 63 mCamera = Camera.open(id); 64 qOpened = (mCamera != null); 65 } catch (Exception e) { 66 Log.e(getString(R.string.app_name), "failed to open Camera"); 67 e.printStackTrace(); 68 } 69 70 return qOpened; 71} 72 73private void releaseCameraAndPreview() { 74 mPreview.setCamera(null); 75 if (mCamera != null) { 76 mCamera.release(); 77 mCamera = null; 78 } 79} 80</pre> 81 82<p>Since API level 9, the camera framework supports multiple cameras. If you use the 83legacy API and call {@link android.hardware.Camera#open open()} without an 84argument, you get the first rear-facing camera.</p> 85 86 87<h2 id="camera-preview">Create the Camera Preview</h2> 88 89<p>Taking a picture usually requires that your users see a preview of their subject before clicking 90the shutter. To do so, you can use a {@link android.view.SurfaceView} to draw previews of what the 91camera sensor is picking up.</p> 92 93<h3 id="TaskSetPreview">Preview Class</h3> 94 95<p>To get started with displaying a preview, you need preview class. The 96preview requires an implementation of the {@code 97android.view.SurfaceHolder.Callback} interface, which is used to pass image 98data from the camera hardware to the application.</p> 99 100<pre> 101class Preview extends ViewGroup implements SurfaceHolder.Callback { 102 103 SurfaceView mSurfaceView; 104 SurfaceHolder mHolder; 105 106 Preview(Context context) { 107 super(context); 108 109 mSurfaceView = new SurfaceView(context); 110 addView(mSurfaceView); 111 112 // Install a SurfaceHolder.Callback so we get notified when the 113 // underlying surface is created and destroyed. 114 mHolder = mSurfaceView.getHolder(); 115 mHolder.addCallback(this); 116 mHolder.setType(SurfaceHolder.SURFACE_TYPE_PUSH_BUFFERS); 117 } 118... 119} 120</pre> 121 122<p>The preview class must be passed to the {@link android.hardware.Camera} object before the live 123image preview can be started, as shown in the next section.</p> 124 125 126<h3 id="TaskStartPreview">Set and Start the Preview</h2> 127 128<p>A camera instance and its related preview must be created in a specific 129order, with the camera object being first. In the snippet below, the 130process of initializing the camera is encapsulated so that {@link 131android.hardware.Camera#startPreview Camera.startPreview()} is called by the 132{@code setCamera()} method, whenever the user does something to change the 133camera. The preview must also be restarted in the preview class {@code 134surfaceChanged()} callback method.</p> 135 136<pre> 137public void setCamera(Camera camera) { 138 if (mCamera == camera) { return; } 139 140 stopPreviewAndFreeCamera(); 141 142 mCamera = camera; 143 144 if (mCamera != null) { 145 List<Size> localSizes = mCamera.getParameters().getSupportedPreviewSizes(); 146 mSupportedPreviewSizes = localSizes; 147 requestLayout(); 148 149 try { 150 mCamera.setPreviewDisplay(mHolder); 151 } catch (IOException e) { 152 e.printStackTrace(); 153 } 154 155 // Important: Call startPreview() to start updating the preview 156 // surface. Preview must be started before you can take a picture. 157 mCamera.startPreview(); 158 } 159} 160</pre> 161 162 163<h2 id="TaskSettings">Modify Camera Settings</h2> 164 165<p>Camera settings change the way that the camera takes pictures, from the zoom 166level to exposure compensation. This example changes only the preview size; 167see the source code of the Camera application for many more.</p> 168 169<pre> 170public void surfaceChanged(SurfaceHolder holder, int format, int w, int h) { 171 // Now that the size is known, set up the camera parameters and begin 172 // the preview. 173 Camera.Parameters parameters = mCamera.getParameters(); 174 parameters.setPreviewSize(mPreviewSize.width, mPreviewSize.height); 175 requestLayout(); 176 mCamera.setParameters(parameters); 177 178 // Important: Call startPreview() to start updating the preview surface. 179 // Preview must be started before you can take a picture. 180 mCamera.startPreview(); 181} 182</pre> 183 184 185<h2 id="TaskOrientation">Set the Preview Orientation</h2> 186 187<p>Most camera applications lock the display into landscape mode because that is the natural 188orientation of the camera sensor. This setting does not prevent you from taking portrait-mode 189photos, because the orientation of the device is recorded in the EXIF header. The {@link 190android.hardware.Camera#setDisplayOrientation setCameraDisplayOrientation()} method lets you change 191how the preview is displayed without affecting how the image is recorded. However, in Android prior 192to API level 14, you must stop your preview before changing the orientation and then restart it.</p> 193 194 195<h2 id="TaskTakePicture">Take a Picture</h2> 196 197<p>Use the {@link android.hardware.Camera#takePicture Camera.takePicture()} 198method to take a picture once the preview is started. You can create {@link 199android.hardware.Camera.PictureCallback} and {@link 200android.hardware.Camera.ShutterCallback} objects and pass them into {@link 201android.hardware.Camera#takePicture Camera.takePicture()}.</p> 202 203<p>If you want to grab images continously, you can create a {@link 204android.hardware.Camera.PreviewCallback} that implements {@link 205android.hardware.Camera.PreviewCallback#onPreviewFrame onPreviewFrame()}. For 206something in between, you can capture only selected preview frames, or set up a 207delayed action to call {@link android.hardware.Camera#takePicture 208takePicture()}.</p> 209 210 211<h2 id="TaskRestartPreview">Restart the Preview</h2> 212 213<p>After a picture is taken, you must restart the preview before the user 214can take another picture. In this example, the restart is done by overloading 215the shutter button.</p> 216 217<pre> 218@Override 219public void onClick(View v) { 220 switch(mPreviewState) { 221 case K_STATE_FROZEN: 222 mCamera.startPreview(); 223 mPreviewState = K_STATE_PREVIEW; 224 break; 225 226 default: 227 mCamera.takePicture( null, rawCallback, null); 228 mPreviewState = K_STATE_BUSY; 229 } // switch 230 shutterBtnConfig(); 231} 232</pre> 233 234 235<h2 id="TaskReleaseCamera">Stop the Preview and Release the Camera</h2> 236 237<p>Once your application is done using the camera, it's time to clean up. In 238particular, you must release the {@link android.hardware.Camera} object, or you risk crashing other 239applications, including new instances of your own application.</p> 240 241<p>When should you stop the preview and release the camera? Well, having your 242preview surface destroyed is a pretty good hint that it’s time to stop the 243preview and release the camera, as shown in these methods from the {@code 244Preview} class.</p> 245 246<pre> 247public void surfaceDestroyed(SurfaceHolder holder) { 248 // Surface will be destroyed when we return, so stop the preview. 249 if (mCamera != null) { 250 // Call stopPreview() to stop updating the preview surface. 251 mCamera.stopPreview(); 252 } 253} 254 255/** 256 * When this function returns, mCamera will be null. 257 */ 258private void stopPreviewAndFreeCamera() { 259 260 if (mCamera != null) { 261 // Call stopPreview() to stop updating the preview surface. 262 mCamera.stopPreview(); 263 264 // Important: Call release() to release the camera for use by other 265 // applications. Applications should release the camera immediately 266 // during onPause() and re-open() it during onResume()). 267 mCamera.release(); 268 269 mCamera = null; 270 } 271} 272</pre> 273 274<p>Earlier in the lesson, this procedure was also part of the {@code 275setCamera()} method, so initializing a camera always begins with stopping the 276preview.</p> 277 278