java - Android 通过套接字发送图像，但在服务器端始终接收到空

Question

我使用 Socket 发送位图，其中客户端是我的 .apk，服务器是 Delphi 可执行文件。

位图发送成功，但服务器接收时，位图为空，大小为0KB。

所以，如果可能的话，我想要任何建议或解决方案，以解决这个问题。

到目前为止，这是我的代码:

Android(客户端)

public class MainActivity extends Activity {

    Socket clientSocket;

    private static final int SERVERPORT = 60;
    private static final String SERVER_IP = "192.168.25.227";

    byte[] tmpbytes = null;


    @Override
    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        new Thread(new ClientThread()).start();

    }

        public Bitmap takeScreenshot() {

           View rootView = findViewById(android.R.id.content).getRootView();
           rootView.setDrawingCacheEnabled(true);
           return rootView.getDrawingCache();

        }

        public void getBytes() throws IOException {

            try
            {

            Bitmap bmp = takeScreenshot();

            int bytes = bmp.getByteCount();
            ByteBuffer buffer = ByteBuffer.allocate(bytes); 
            bmp.copyPixelsToBuffer(buffer); 

            byte[] array = buffer.array(); 
            int start=0;
            int len=array.length;
            if (len < 0)
            throw new IllegalArgumentException("Negative length not allowed");
            if (start < 0 || start >= array.length)
            throw new IndexOutOfBoundsException("Out of bounds: " + start);

            OutputStream out = clientSocket.getOutputStream(); 
            DataOutputStream dos = new DataOutputStream(out);

            dos.writeInt(len);
            if (len > 0) {
            dos.write(array, start, len);
            }



          }

            catch (UnknownHostException e) {
                //System.out.println(e.toString());
            } 

            catch (IOException e) {
                //System.out.println(e.toString());
            } 

            catch (Exception e1) {
                //Log.e("clients", e1.toString());
                //Toast.makeText(MainActivity.this, e1.toString(), Toast.LENGTH_LONG).show();
                System.out.println(e1.toString());
            }

        }

        class ClientThread implements Runnable { 

            @Override
            public void run() {

                try {

                    InetAddress serverAddr = InetAddress.getByName(SERVER_IP);

                    clientSocket = new Socket(serverAddr, SERVERPORT);

                    //new Thread(new CommsThread()).start();

                    Thread.sleep(1000);

                    getBytes();

                } catch (Exception e1) {
                    //Log.e("clients", e1.toString());
                    //Toast.makeText(MainActivity.this, e1.toString(), Toast.LENGTH_LONG).show();
                    System.out.println(e1.toString());
                } 

            }
        }

}

Delphi(服务器)

var
 Form1: TForm1;

stSize: integer;   
Stream: TMemoryStream; 
bmp: TBitmap; 
FSize: Integer;
writing: Boolean;

procedure TForm1.FormCreate(Sender: TObject);
begin
Stream:= TMemoryStream.Create;
writing:= False;
end;

procedure TForm1.ServerSocket1ClientRead(Sender: TObject;
  Socket: TCustomWinSocket);
var
  BytesReceived: Longint;
  CopyBuffer: Pointer; { buffer for copying }
  ChunkSize: Integer;
  TempSize: Integer;
const
  MaxChunkSize: Longint = 8192; { copy in 8K chunks }
begin

  If FSize=0 then
  begin
    If Socket.ReceiveLength>SizeOf(TempSize) then
    begin
      Socket.ReceiveBuf(TempSize,SizeOf(TempSize));
      Stream.SetSize(TempSize);
      FSize:= TempSize //Threadsafe code!
    End;
  End;

  If (FSize>0) and not(writing) then
  begin
    GetMem(CopyBuffer, MaxChunkSize); { allocate the buffer }
    writing:= True;
    While Socket.ReceiveLength>0 do
    Begin
      ChunkSize:= Socket.ReceiveLength;
      If ChunkSize > MaxChunkSize then ChunkSize:= MaxChunkSize;
      BytesReceived:= Socket.ReceiveBuf(CopyBuffer^,ChunkSize);
      Stream.Write(CopyBuffer^, BytesReceived); { ...write chunk }
      Dec(FSize,BytesReceived);
    End;
  end;

  If FSize=0 then begin

  Stream.Position := 0;
  bmp:=TBitmap.Create; 
  bmp.LoadFromStream(Stream); 
  Image1.Picture.Graphic := bmp; 
  Stream.SetSize(0);
  bmp.Free;
  FSize:= 0;
end;

FreeMem(CopyBuffer, MaxChunkSize); { allocate the buffer }
Writing:= False;
end;

:

经过 Remy Lebeau 的建议，我所做的更改仍然不起作用:-(

德尔福

procedure TForm1.ServerSocket1ClientRead(Sender: TObject;
  Socket: TCustomWinSocket);
var
  BytesReceived: Longint;
  CopyBuffer: Pointer;
  ChunkSize: Integer;
  TempSize: Integer;
const
  MaxChunkSize: Longint = 8192;
begin

  If FSize=0 then
  begin
    If Socket.ReceiveLength>SizeOf(TempSize) then
    begin
      Socket.ReceiveBuf(TempSize,SizeOf(TempSize));
      TempSize := ntohl(TempSize); // Changed to ntohl
      Stream.SetSize(TempSize);
      FSize:= TempSize
    End;
  End;

  If (FSize>0) and not(writing) then
  begin
    GetMem(CopyBuffer, MaxChunkSize);
    writing:= True;
    While Socket.ReceiveLength>0 do
    Begin
      ChunkSize:= Socket.ReceiveLength;
      If ChunkSize > MaxChunkSize then ChunkSize:= MaxChunkSize;
      BytesReceived:= Socket.ReceiveBuf(CopyBuffer^,ChunkSize);
      Stream.Write(CopyBuffer^, BytesReceived);
      Dec(FSize,BytesReceived);
    End;
  end;

  If FSize=0 then begin

  Stream.Position := 0;
  png:=TPngImage.Create;  // Changed to TPNGImage here
  png.LoadFromStream(Stream);
  Image1.Picture.Assing(png);
  Stream.SetSize(0);
  png.Free;
  FSize:= 0;
end;

FreeMem(CopyBuffer, MaxChunkSize);
Writing:= False;
end;

Android

public void getBytes() throws IOException {

            try
            {

            Bitmap bmp = takeScreenshot();

            ByteArrayOutputStream bos = new ByteArrayOutputStream(); 
            bmp.compress(CompressFormat.PNG, 0 /*ignored for PNG*/, bos); 
            byte[] array = bos.toByteArray();
            OutputStream out = socket.getOutputStream(); 
            DataOutputStream dos = new DataOutputStream(out);
            dos.writeInt(array.length);
            dos.write(array, 0, array.length);

          }

            catch (UnknownHostException e) {
                //System.out.println(e.toString());
            } 

            catch (IOException e) {
                //System.out.println(e.toString());
            } 

            catch (Exception e1) {
                //Log.e("clients", e1.toString());
                //Toast.makeText(MainActivity.this, e1.toString(), Toast.LENGTH_LONG).show();
                System.out.println(e1.toString());
            }

        }

Answer 1

您的代码存在很多问题。

您没有关注ReceiveBuf()的返回值。它返回实际读取的字节数，该字节数可能比您请求的字节数少，或者在断开连接时返回 0，或在出错时返回 -1(尤其是在非阻塞模式下使用服务器时)。你需要处理这些情况。您需要循环读取 TempSize 。当您恰好收到 FSize 时，您需要停止循环。读取像素时的字节数。

您没有考虑字节序。 DataOutputStream.writeInt()以大端字节顺序写入整数字节。 Windows 上的 Delphi 是小端。您调用ReceiveBuf(TempSize,SizeOf(TempSize))正在按原样读取整数字节，因此 TempSize将采用大尾数法。在使用之前，您需要将值转换为小端字节序。您可以使用ntohl()为此:

TempSize := ntohl(TempSize);

您的客户端仅发送原始像素数据，但是 TBitmap.LoadFrom...()需要完整的.bmp文件，包括BITMAPFILEHEADER和BITMAPINFOHEADER描述位图及其像素的 header (请参阅 Bitmap Storage )。您需要发送这些 header ，或者至少填充您的 Stream在将像素读入其中之前先使用它们。

但是，Android 对 bmp 没有很好的支持格式，所以你最好使用 Bitmap.compress()将位图数据提取为 PNG，然后使用 TPNGImage在 Delphi 端加载它。