安卓开发常用知识点& 安卓开发常见问题及解决方案
2021-08-08 15:44:29

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

@Override
protected 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
@Override
protected 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’

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

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：

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” }

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。。。