常用知識點===

一,Activity相關

• 1，判斷activity是在前臺運行，還是在后臺運行

//當前activity是否在前臺顯示
    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", "前臺");
                return true;
            } else {
                Log.i("qcl0403", "后臺");
            }
        }
        return false;
    }

• 2，acitivity設置為singleTop或singleTask 模式時，相關文章跳本activity調整數據不改變問題

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

二，View相關

• 1 判斷當前view是否在前臺展示,我們這里以recyclerView為例

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是我們窗口狀態(tài)改變時回傳回來的值
                    true： 我們的view在前臺展示
                    fasle: 熄屏，onpause，后臺時展示 
                    我們如果在每次熄屏到亮屏也算一次曝光的話，那這里為true的時候可以做統計
                    */

                }
            });
        }

• 2,RecyclerView滾動到指定位置，并置頂

LinearSmoothScroller smoothScroller = new LinearSmoothScroller
        (ArticleDetailActivity.this) {
    @Override
    protected int getVerticalSnapPreference() {
        return LinearSmoothScroller.SNAP_TO_START;
    }
//設置滑動1px所需時間
@Override
protected float calculateSpeedPerPixel
(DisplayMetrics displayMetrics) {
    //縮短每px的滑動時間
    float MILLISECONDS_PER_INCH = getResources().getDisplayMetrics()
            .density * 0.03f;
    return MILLISECONDS_PER_INCH / displayMetrics.density;
    //返回滑動一個pixel需要多少毫秒
}
};
smoothScroller.setTargetPosition(position);
virtualLayoutManager.startSmoothScroll(smoothScroller);

三，適配相關

-1,判斷手機是否有底部虛擬按鍵

   /*
    * 判斷手機是否有底部虛擬按鍵
    * */
    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，解決popupwindow在7.0以上機型設置居于view下方卻蓋在了view上面的問題

  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());
            }

常見問題============ 一，androidstudio編譯相關

1， Error while Installing APK

解決方案：重新sync按鈕編譯下gradle就可以了

2，出現Execution failed for task類的錯誤

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

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

解決方案：
首先找到Execution failed for task,然后取到后面的如上面紅框里的信息
在命令行執(zhí)行
./gradlew app:transformDexArchiveWithExternalLibsDexMergerForDebug --stacktrace --info
或者
./gradlew compileDebugJavaWithJavac --stackstrace
執(zhí)行完成以后，搜索‘錯誤’就可以看到具體錯誤原因了

或者運行下面然后查看 Caused by的地方
./gradlew compileDebugSources --stacktrace -info

3 Could not find support-media-compat.aar

升級android studio到3.3版本，今天checkout到歷史tag上運行android項目，死活報錯
之前也有同事遇到過類似的問題： Could not find support-media-compat.aar

最后意外發(fā)現是google()倉庫位置的問題
報錯配置：

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 如下圖：

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

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

在app的gradle文件中加入下面這句話：

android {
    .....
    defaultConfig {
        ......
	//在下面添加這句話，然后重新編譯，就OK了。
        javaCompileOptions { annotationProcessorOptions { includeCompileClasspath = true } }
    }

持續(xù)更新中。。。