========常用知识点===========

一,Activity相关

• 1，判断activity是在前台运行，还是在后台运行

//当前activity是否在前台显示    private boolean isAPPforeground(final Context context) {        ActivityManager am = (ActivityManager) context.getSystemService(Context.ACTIVITY_SERVICE);        List<ActivityManager.RunningTaskInfo> tasks = am.getRunningTasks(1);        if (!tasks.isEmpty()) {            ComponentName topActivity = tasks.get(0).topActivity;            if (topActivity.getClassName().equals(context.getClass().getName())) {                Log.i("qcl0403", "前台");                return true;            } else {                Log.i("qcl0403", "后台");            }        }        return false;    }

• 2，acitivity设置为singleTop或singleTask 模式时，相关文章跳本activity调整数据不改变问题

@Overrideprotected void onNewIntent(Intent intent) {    super.onNewIntent(intent);    setIntent(intent);    ARouter.getInstance().inject(this);}

二，View相关

• 1 判断当前view是否在前台展示,我们这里以recyclerView为例

ViewTreeObserver treeObserver = recyclerView.getViewTreeObserver();        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.JELLY_BEAN_MR2) {            treeObserver.addOnWindowFocusChangeListener(new ViewTreeObserver.OnWindowFocusChangeListener() {                @Override                public void onWindowFocusChanged(boolean hasFocus) {                    /*                    hasFocus是我们窗口状态改变时回传回来的值                    true： 我们的view在前台展示                    fasle: 熄屏，onpause，后台时展示                     我们如果在每次熄屏到亮屏也算一次曝光的话，那这里为true的时候可以做统计                    */                }            });        }

• 2,RecyclerView滚动到指定位置，并置顶

LinearSmoothScroller smoothScroller = new LinearSmoothScroller        (ArticleDetailActivity.this) {    @Override    protected int getVerticalSnapPreference() {        return LinearSmoothScroller.SNAP_TO_START;    }//设置滑动1px所需时间@Overrideprotected float calculateSpeedPerPixel(DisplayMetrics displayMetrics) {    //缩短每px的滑动时间    float MILLISECONDS_PER_INCH = getResources().getDisplayMetrics()            .density * 0.03f;    return MILLISECONDS_PER_INCH / displayMetrics.density;    //返回滑动一个pixel需要多少毫秒}};smoothScroller.setTargetPosition(position);virtualLayoutManager.startSmoothScroll(smoothScroller);

三，适配相关

-1,判断手机是否有底部虚拟按键

   /*    * 判断手机是否有底部虚拟按键    * */    public boolean checkDeviceHasNavigationBar(Context context) {        boolean hasNavigationBar = false;        Resources rs = context.getResources();        int id = rs.getIdentifier("config_showNavigationBar", "bool", "android");        if (id > 0) {            hasNavigationBar = rs.getBoolean(id);        }        try {            Class systemPropertiesClass = Class.forName("android.os.SystemProperties");            Method m = systemPropertiesClass.getMethod("get", String.class);            String navBarOverride = (String) m.invoke(systemPropertiesClass, "qemu.hw.mainkeys");            if ("1".equals(navBarOverride)) {                hasNavigationBar = false;            } else if ("0".equals(navBarOverride)) {                hasNavigationBar = true;            }        } catch (Exception e) {        }        return hasNavigationBar;    }

• 2，解决popupwindow在7.0以上机型设置居于view下方却盖在了view上面的问题

  if (Build.VERSION.SDK_INT < 24) {                popupWindow.showAsDropDown(v);            } else {                int[] location = new int[2];                v.getLocationOnScreen(location);                int x = location[0];                int y = location[1];                popupWindow.showAtLocation(v, Gravity.NO_GRAVITY, 0, y + v.getHeight());            }

======常见问题==================

一，androidstudio编译相关

1， Error while Installing APK

解决方案：重新sync按钮编译下gradle就可以了

2，出现Execution failed for task类的错误

Error:Execution failed for task ‘:app:compileDebugJavaWithJavac’.
Compilation failed; see the compiler error output for details.

TaskExecutionException: Execution failed for task ‘:app:transformClassesWithAspectTransformForDebug’

image.png

解决方案：
首先找到Execution failed for task,然后取到后面的如上面红框里的信息
在命令行执行
./gradlew app:transformDexArchiveWithExternalLibsDexMergerForDebug –stacktrace –info
或者
./gradlew compileDebugJavaWithJavac –stackstrace
执行完成以后，搜索‘错误’就可以看到具体错误原因了

或者运行下面然后查看 Caused by的地方
./gradlew compileDebugSources –stacktrace -info

3 Could not find support-media-compat.aar

升级android studio到3.3版本，今天checkout到历史tag上运行android项目，死活报错
之前也有同事遇到过类似的问题： Could not find support-media-compat.aar

image.png

最后意外发现是google()仓库位置的问题
报错配置：

allprojects {    repositories {        flatDir {            dirs 'libs'        }        jcenter()        maven { url "https://jitpack.io" }        maven { url "https://dl.bintray.com/thelasterstar/maven/" }        maven {            url "http://maven.aliyun.com/nexus/content/repositories/releases"        }        mavenCentral()        google()    }    configurations.all {        resolutionStrategy {            force "com.android.support:appcompat-v7:$supportLibVersion"        }    }}

把google()放到第一位即可

allprojects {    repositories {        google()        flatDir {            dirs 'libs'        }        jcenter()        maven { url "https://jitpack.io" }        maven { url "https://dl.bintray.com/thelasterstar/maven/" }        maven {            url "http://maven.aliyun.com/nexus/content/repositories/releases"        }        mavenCentral()    }    configurations.all {        resolutionStrategy {            force "com.android.support:appcompat-v7:$supportLibVersion"        }    }}

4,could not find com.android.support:appconpat 如下图：

image.png

需要在project的build.gradle中allprojects 添加如下配置即可，添加下面代码到第一行。
maven { url “https://maven.google.com” }

image.png

5，报错：Annotation processors must be explicitly declared now.

在app的gradle文件中加入下面这句话：

android {    .....    defaultConfig {        ......    //在下面添加这句话，然后重新编译，就OK了。        javaCompileOptions { annotationProcessorOptions { includeCompileClasspath = true } }    }

持续更新中。。。

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