1、要实现的功能：在App上点击”变透明“的按钮后，App的背景色先变为透明，等等10秒后，再把背景色改为半透明（alpha值为0.5）Show the code:AndroidManifest.xml:<LinearLayout android:layout_width="fill_parent" android:layout_height="wrap_content" android:gravity="center" android:orientation="horizontal"> <Button android:id="@+id/clickTransparency" android:layout_width="wrap_content" android:layout_height="wrap_content" android:onClick="turnTransparencyClickHandler" android:text="变透明" />MainActivity.javapublic void turnTransparencyClickHandler(View view) { changeBackgroundAlphaTo(0.0f);}private void changeBackgroundAlphaTo(final float alphaValue) { new Thread(new Runnable() { @Override public void run() { final WindowManager.LayoutParams attributes = getWindow().getAttributes(); attributes.alpha = alphaValue;//０.０全透明．１.０不透明． getWindow().setAttributes(attributes); } }).start();}
2、执行上述代码。在App中点击”变透明“的按钮后，App就退出了。logcat中打祥缮乖贝印了这个错：03-20 14:47:31.326 11640-11796/com.example.cy.myapplication E/AndroidRuntime: FATAL EXCEPTION: Thread-1565103-20 14:47:31.326 11640-11796/com.example.cy.myapplication E/AndroidRuntime: Process: com.example.cy.myapplication, PID: 1164003-20 14:47:31.326 11640-11796/com.example.cy.myapplication E/AndroidRuntime: android.view.ViewRootImpl$CalledFromWrongThreadException: Only the original thread that created a view hierarchy can touch its views.03-20 14:47:31.326 11640-11796/com.example.cy.myapplication E/AndroidRuntime: at android.view.ViewRootImpl.checkThread(ViewRootImpl.java:6090)03-20 14:47:31.326 11640-11796/com.example.cy.myapplication E/AndroidRuntime: at android.view.ViewRootImpl.requestLayout(ViewRootImpl.java:879)03-20 14:47:31.326 11640-11796/com.example.cy.myapplication E/AndroidRuntime: at android.view.View.requestLayout(View.java:16463)03-20 14:47:31.326 11640-11796/com.example.cy.myapplication E/AndroidRuntime: at android.view.View.setLayoutParams(View.java:10593)03-20 14:47:31.326 11640-11796/com.example.cy.myapplication E/AndroidRuntime: at android.view.WindowManagerGlobal.updateViewLayout(WindowManagerGlobal.java:292)03-20 14:47:31.326 11640-11796/com.example.cy.myapplication E/AndroidRuntime: at android.view.WindowManagerImpl.updateViewLayout(WindowManagerImpl.java:74)03-20 14:47:31.326 11640-11796/com.example.cy.myapplication E/AndroidRuntime: at android.app.Activity.onWindowAttributesChanged(Activity.java:2347)03-20 14:47:31.326 11640-11796/com.example.cy.myapplication E/AndroidRuntime: at android.support.v7.internal.view.WindowCallbackWrapper.onWindowAttributesChanged(WindowCallbackWrapper.java:105)03-20 14:47:31.326 11640-11796/com.example.cy.myapplication E/AndroidRuntime: at android.view.Window.setAttributes(Window.java:847)03-20 14:47:31.326 11640-11796/com.example.cy.myapplication E/AndroidRuntime: at com.example.cy.myapplication.MainActivity$1.run(MainActivity.java:78)03-20 14:47:31.326 11640-11796/com.example.cy.myapplication E/AndroidRuntime: at java.lang.Thread.run(Thread.java:841)
3、和Swing中的用法还不一样啊。哪就在UI线程中更新吧。Android中有个组件andro坡纠课柩id.os.Handler的postDelayed可以解决这个问题源码:/** * Causes the Runnable r to be added to the message queue, to be run * after the specified amount of time elapses. * The runnable will be run on the thread to which this handler * is attached. * <b>The time-base is {@link android.os.SystemClock#uptimeMillis}.</b> * Time spent in deep sleep will add an additional delay to execution. * * @param r The Runnable that will be executed. * @param delayMillis The delay (in milliseconds) until the Runnable * will be executed. * * @return Returns true if the Runnable was successfully placed in to the * message queue. Returns false on failure, usually because the * looper processing the message queue is exiting. Note that a * result of true does not mean the Runnable will be processed -- * if the looper is quit before the delivery time of the message * occurs then the message will be dropped. */public final boolean postDelayed(Runnable r, long delayMillis){ return sendMessageDelayed(getPostMessage(r), delayMillis);}
4、改改刚才报错的代码Code:MainActivity.java:定义一个字段private Handler handler = new Handler();public void turnTransparencyClickHandler(View view) { changeBackgroundAlphaTo(0.0f); handler.postDelayed(new Runnable() { @Override public void run() { Log.i("turnTransparency", "begin to change alpha to 0.5"); changeBackgroundAlphaTo(0.5f); Log.i("turnTransparency", "end to change alpha to 0.5"); } }, 10 * 1000);}private void changeBackgroundAlphaTo(float alphaValue) { WindowManager.LayoutParams attributes = getWindow().getAttributes(); attributes.alpha = alphaValue;//０.０全透明．１.０不透明． getWindow().setAttributes(attributes);}
5、执行下,看看是否达到预期效果达到了，Success！
6、从截图看不出这个变化。在执行变成半透明的代码中，加有日志打印，在logcat中看看能否找到日志：03-20 15:16:14.986 16571-16571/com.example.cy.myapplication I/turnTransparency: begin to change alpha to 0.503-20 15:16:14.986 16571-16571/com.example.cy.myapplication I/turnTransparency: end to change alpha to 0.5
