发表更新OI KIWI / 算法12 分钟读完 (大约1789个字)

OI KIWI 01-倍增

OI KIWI 倍增

思想

图片来源

查找小于limit的最大数字

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int maxValueInVecSmallerThenLimit(vector<int>& vec, int limit) {
    int n = vec.size();
    int l = 0;
    int p = 1;
    while(p) {
        if(l + p < n && vec[l + p] < limit) {
            l += p;
            p <<= 1;
        } else {
            p >>= 1;
        }
    }
    return vec[l];
}
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发表更新LeetCode / 算法44 分钟读完 (大约6551个字)

LeetCode-36

551. 学生出勤记录 I

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class Solution {
public:
    bool checkRecord(string s) {
        int count = 0;
        int max_seq_late = 0;
        int seq_late = 0;
        for(char c : s) {
            if(c == 'A') count++;
            if(c == 'L') {
                seq_late++;
            } else {
                max_seq_late = max(max_seq_late, seq_late);
                seq_late = 0;
            }
        }
        max_seq_late = max(max_seq_late, seq_late);
        return count < 2 && max_seq_late < 3;

    }
};
  • 连续相同的值的个数
  • 统计元素出现的次数

3137. K 周期字符串需要的最少操作次数

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class Solution {
public:
    int minimumOperationsToMakeKPeriodic(string word, int k) {
        unordered_map<string, int> subStrCount;
        int len = word.length();
        for(int i = 0; i < len; i += k) {
            subStrCount[word.substr(i, k)]++;
        }
        int minOpCnt = len / k;
        for(auto& ite : subStrCount) {
            minOpCnt = min(minOpCnt, len / k - ite.second);
        }
        return minOpCnt;
    }
};
  • 翻译一下规则，就是把长度为nk的字符串切割成n个长度为k的子串，一次操作可以把一个子串替换成另一个字串，求如何替换，将所有字串都相同。
  • 翻译好需求，就很清楚了，直接统计每个字串出现的次数，取出现次数最大的，替换次数最少，为n - cnt[i]
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发表更新Android / 手撸Android源码1 小时读完 (大约11066个字)

基础05-Navigation

简介

NavController是中央导航 API。它会跟踪用户访问过的目的地，并允许用户在目的地之间移动。

获取NavController

  • fragment

如果是NavHostFragment

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val navController = this.navController
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发表更新Android / 手撸Android源码23 分钟读完 (大约3407个字)

基础04-LiveData

LiveData

LiveData的观察者

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fun interface Observer<T> {

    /**
     * Called when the data is changed to [value].
     */
    fun onChanged(value: T)
}
  • 通过onChanged函数分派数据变化

成员

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@SuppressWarnings("WeakerAccess") /* synthetic access */
final Object mDataLock = new Object();
static final int START_VERSION = -1;
@SuppressWarnings("WeakerAccess") /* synthetic access */
static final Object NOT_SET = new Object();

private SafeIterableMap<Observer<? super T>, ObserverWrapper> mObservers =
        new SafeIterableMap<>();

// how many observers are in active state
@SuppressWarnings("WeakerAccess") /* synthetic access */
int mActiveCount = 0;
// to handle active/inactive reentry, we guard with this boolean
private boolean mChangingActiveState;
private volatile Object mData; // 1️⃣：当前的data
// when setData is called, we set the pending data and actual data swap happens on the main
// thread
@SuppressWarnings("WeakerAccess") /* synthetic access */
volatile Object mPendingData = NOT_SET; // 2️⃣：给多线程使用的，在4️⃣mPostValueRunnable中使用
private int mVersion; // 3️⃣：mVersion是数据版本

private boolean mDispatchingValue;
@SuppressWarnings("FieldCanBeLocal")
private boolean mDispatchInvalidated;
private final Runnable mPostValueRunnable = new Runnable() {// 4️⃣mPostValueRunnable，在主线程中将mPendingData设置为当前值
    @SuppressWarnings("unchecked")
    @Override
    public void run() {
        Object newValue;
        synchronized (mDataLock) {
            newValue = mPendingData;
            mPendingData = NOT_SET;
        }
        setValue((T) newValue);
    }
};
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发表更新Android / 手撸Android源码21 分钟读完 (大约3102个字)

基础02-viewModel

ViewModel简介

在了解ViewModel之前，我们先来了解一下MVC, MVP, MVVM的发展Difference Between MVC, MVP and MVVM Architecture Pattern in Android

ViewModelStoreOwner

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interface ViewModelStoreOwner {

    /**
     * The owned [ViewModelStore]
     */
    val viewModelStore: ViewModelStore
}

ViewModelStore

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发表更新Android / 手撸Android源码18 分钟读完 (大约2687个字)

基础03-Lifecycle

lifeCycle的Observer

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public interface LifecycleObserver

public interface DefaultLifecycleObserver : LifecycleObserver {
    /**
     * Notifies that `ON_CREATE` event occurred.
     *
     *
     * This method will be called after the [LifecycleOwner]'s `onCreate`
     * method returns.
     *
     * @param owner the component, whose state was changed
     */
    public fun onCreate(owner: LifecycleOwner) {}

    /**
     * Notifies that `ON_START` event occurred.
     *
     *
     * This method will be called after the [LifecycleOwner]'s `onStart` method returns.
     *
     * @param owner the component, whose state was changed
     */
    public fun onStart(owner: LifecycleOwner) {}

    /**
     * Notifies that `ON_RESUME` event occurred.
     *
     *
     * This method will be called after the [LifecycleOwner]'s `onResume`
     * method returns.
     *
     * @param owner the component, whose state was changed
     */
    public fun onResume(owner: LifecycleOwner) {}

    /**
     * Notifies that `ON_PAUSE` event occurred.
     *
     *
     * This method will be called before the [LifecycleOwner]'s `onPause` method
     * is called.
     *
     * @param owner the component, whose state was changed
     */
    public fun onPause(owner: LifecycleOwner) {}

    /**
     * Notifies that `ON_STOP` event occurred.
     *
     *
     * This method will be called before the [LifecycleOwner]'s `onStop` method
     * is called.
     *
     * @param owner the component, whose state was changed
     */
    public fun onStop(owner: LifecycleOwner) {}

    /**
     * Notifies that `ON_DESTROY` event occurred.
     *
     *
     * This method will be called before the [LifecycleOwner]'s `onDestroy` method
     * is called.
     *
     * @param owner the component, whose state was changed
     */
    public fun onDestroy(owner: LifecycleOwner) {}
}

public fun interface LifecycleEventObserver : LifecycleObserver {
    /**
     * Called when a state transition event happens.
     *
     * @param source The source of the event
     * @param event The event
     */
    public fun onStateChanged(source: LifecycleOwner, event: Lifecycle.Event)
}
  • 可以看到，我们在使用lifecycle.addObserver()时，可以传入LifecycleEventObserver或DefaultLifecycleObserver，一个通过event获取当前状态，一个通过不同的回调函数获取当前状态

Activity树

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Activity -- AccountAuthenticatorActivity
         |- ActivityGroup -- TabActivity
         |- ExpandableListActivity
         |- LauncherActivity
         |- ListActivity -- PreferenceActivity
         |- NativeActivity
         |- androidx.core.app.ComponentActivity -- androidx.activity.ComponentActivity -- FragmentActivity -- AppCompatActivity
                                                |- PreviewActivity
         |- BootstrapActivity
         |- EmptyActivity
         |- EmptyFloatingActivity

LifecycleOwner

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发表更新misc5 分钟读完 (大约700个字)

MIUISupermarket移植

VerifyError

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java.lang.VerifyError: Verifier rejected class com.xiaomi.market.util.UIUtils: void com.xiaomi.market.util.UIUtils.setStatusBarDarkMode(android.app.Activity, boolean) failed to verify: void com.xiaomi.market.util.UIUtils.setStatusBarDarkMode(android.app.Activity, boolean): [0x15] type Undefined unexpected as arg to if-eqz/if-nez (declaration of 'com.xiaomi.market.util.UIUtils' appears in /data/app/~~pH0reBrzyfvMag1T-TAoDw==/com.xiaomi.market-EzZXS_MznmhQs5NCCbvqfA==/base.apk!classes2.dex)
  • 一般出现VerifyError都是因为对smali代码修改，导致无法通过验证。当前遇到过的情况有：
    • 插入代码时无意覆盖了下面会用到的寄存器的值，导致寄存器类型不匹配等问题。
    • 对方法参数类型修改但未修改调用时传入的参数
    • 传递参数时传递了类型不匹配的参数

ClassNotFound

在xiaomi商店中使用了Lmiui/os/Build类，该类继承Landroid/os/Build，且存在于小米系统中，导致类找不到。导致运行时闪退。

对于这类小米系统中才能获取到的类，采用等价替换的方法进行修复。如在Lmiui/os/Build中有：

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发表更新Android / 手撸Android源码27 分钟读完 (大约3993个字)

基础01-Context

大纲

  • Context类
    • 注解
      • 用于标注文件、SharedPreferences、数据库的打开方式的注解
      • 用于标注bindService时，service的flags的注解
      • 用于标注registerReceiver时，receiver的flags的注解
      • 用于标注getService时，servicesName的注解
      • 用于标注createPackageContext、createPackageContextAsUser、createContextAsUser、createApplicationContext时的flags的注解
    • 常量定义
      • 对应上面注解中限制的常量
      • WAL

Context类

Context是抽象类，具体实现在ContextImpl，Application，Service，Activity都直接或间接继承自ContextWrapper，ContextWrapper通过代理的方式调用真正的ContextImpl。

注解

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/** @hide */
@IntDef(flag = true, prefix = { "MODE_" }, value = {
        MODE_PRIVATE,
        MODE_WORLD_READABLE,
        MODE_WORLD_WRITEABLE,
        MODE_APPEND,
})
@Retention(RetentionPolicy.SOURCE)
public @interface FileMode {}

/** @hide */
@IntDef(flag = true, prefix = { "MODE_" }, value = {
        MODE_PRIVATE,
        MODE_WORLD_READABLE,
        MODE_WORLD_WRITEABLE,
        MODE_MULTI_PROCESS,
})
@Retention(RetentionPolicy.SOURCE)
public @interface PreferencesMode {}

/** @hide */
@IntDef(flag = true, prefix = { "MODE_" }, value = {
        MODE_PRIVATE,
        MODE_WORLD_READABLE,
        MODE_WORLD_WRITEABLE,
        MODE_ENABLE_WRITE_AHEAD_LOGGING,
        MODE_NO_LOCALIZED_COLLATORS,
})
@Retention(RetentionPolicy.SOURCE)
public @interface DatabaseMode {}
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发表更新Android11 分钟读完 (大约1717个字)

01-layout

ID

创建 RelativeLayout 时，请务必为视图对象定义 ID。在相对布局中，同级视图可以定义其相对于通过唯一 ID 引用的另一个同级视图的布局。

findViewById

ID 不必在整个树状结构中具有唯一性，但在您搜索的树状结构部分中必须是唯一的。它通常可能是整个树，因此最好尽可能使其具有唯一性。

  • findViewById是View的方法
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/**
 * Finds the first descendant view with the given ID, the view itself if
 * the ID matches {@link #getId()}, or {@code null} if the ID is invalid
 * (< 0) or there is no matching view in the hierarchy.
 * <p>
 * <strong>Note:</strong> In most cases -- depending on compiler support --
 * the resulting view is automatically cast to the target class type. If
 * the target class type is unconstrained, an explicit cast may be
 * necessary.
 *
 * @param id the ID to search for
 * @return a view with given ID if found, or {@code null} otherwise
 * @see View#requireViewById(int)
 */
@Nullable
public final <T extends View> T findViewById(@IdRes int id) {
    if (id == NO_ID) {
        return null;
    }
    return findViewTraversal(id);
}
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发表更新git几秒读完 (大约108个字)

git的使用

版本控制发展历史

本地代码版本控制

RCS: 只能保存本地的变化情况，无法协同合作

集中式版本控制

SVN: 远端服务器维护版本，本地不保存代码版本

分布式版本控制

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