Flutter学习笔记

问题

1. Exception in thread “main” java.util.zip.ZipException: zip END header not found

 **For mac user:** open terminal and execute

 >   cd ~

 >   rm -rf .gradle

 **For windows user:**

 Go to the root directory C:\Users\YourUser and locate the hidden .gradle folder and delete it. and then run your app connected to an Android emulator or device, don't cancel and make have a stable internet connection, this will download fresh Gradle

 [Flutter: Exception in thread "main" java.util.zip.ZipException: error in opening zip file](https://stackoverflow.com/questions/60899075/flutter-exception-in-thread-main-java-util-zip-zipexception-error-in-opening)

 我的解决方案：手动下载https\://services.gradle.org/distributions/gradle-7.5-all.zip到`C:\Users\xxx\.gradle\wrapper\dists\gradle-7.5-all\xxx`

2. adb: failed to install

 In your manifest, add `android:exported="true"`.

 example:

 
<activity
        android:name="com.example.packssas.MainActivity"
        android:exported="true">
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />
            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
    </activity>
 
 用`adb shell` 验证，安卓真机和仿真器同时只能有一个启动

3. Flutter（Dart）udp组播，本地调试可以成功抓到数据包，但在apk中使用未抓到数据包

4. The lower bound of “sdk: ‘>=2.2.0 ❤️.0.0’” must be 2.12.0 or higher to enable null safety.

   https://blog.csdn.net/wuqingsen1/article/details/121519297

   environment:
     sdk: '>=2.11.0 <3.0.0'

5. chrome://inspect

6. 比特流转换

   Your data contains 28 bytes, and since it represents 32-bit float values (each of which are 4 bytes), that’s equivalent to seven 32-bit values.

   final data = [
     123, 34,  106, 115,   // 1
     111, 110, 114, 112,   // 2
     99,  34,  58,  34,    // 3
     50,  46,  48,  34,    // 4
     44,  34,  109, 101,   // 5
     116, 104, 111, 100,   // 6
     34,  58,  34,  115,   // 7
   ];

   The ByteData class from the dart:typed_data library gives you different views on byte data. What you want is the Float32 view, which will give you a double in Dart.

   final bytes = Uint8List.fromList(data);
   final byteData = ByteData.sublistView(bytes);
   double value = byteData.getFloat32(0);
   print(value); // 8.433111377393183e+35

   The 0 in getFloat32(0) means that you want to get the 32-bit float value starting at index 0 in the byte array. That only gives you the first value of the seven, though, so if you want the rest you need to loop though the entire byte list:

   for (var i = 0; i < data.length; i += 4) {
     print(byteData.getFloat32(i));
   }

   On every loop you increase the index by 4 to get the beginning of the next 32-bit float value. Run that loop and you’ll see the results for all seven values:

   8.433111377393183e+35
   7.3795778785962275e+28
   2.9925614505443553e+21
   1.0139077133430874e-8
   2.308231080230816e-12
   7.366162972792583e+31
   2.522593777484324e-18

   Uint8List intBytes = Uint8List.fromList([63, 158, 184, 82]);
    ByteData byteData = intBytes.buffer.asByteData();
    List<double> floatList = [
      for (var offset = 0; offset < intBytes.length; offset += 4)
        byteData.getFloat32(offset, Endian.big),
    ];
    print(floatList);