Android Media Player 状态机

状态机图例

图源自谷歌官方API

MediaPlayer State

具体方法API介绍和使用参看

【Android 多媒体开发】 MediaPlayer 状态机接口方法解析

状态检测

在MediaPlayer 开发过程中有的朋友会遇到过 -38错误，为什么是-38呢，简单追踪下流程

看一个Nuplayer 示例

frameworks/av/media/libmediaplayerservice/nuplayer/NuPlayerDriver.cpp

616 status_t NuPlayerDriver::reset() {
617    ALOGD("reset(%p) at state %d", this, mState);
618
619    updateMetrics("reset");
620    logMetrics("reset");
621
622    Mutex::Autolock autoLock(mLock);
623
624    switch (mState) {
625        case STATE_IDLE:
626            return OK;
627
628        case STATE_SET_DATASOURCE_PENDING:
629        case STATE_RESET_IN_PROGRESS:
630            return INVALID_OPERATION;
631
632        case STATE_PREPARING:
633        {
634            CHECK(mIsAsyncPrepare);
635
636            notifyListener_l(MEDIA_PREPARED);
637            break;
638        }
639
640        default:
641            break;
642    }
643
644    if (mState != STATE_STOPPED) {
645        notifyListener_l(MEDIA_STOPPED);
646    }
647
648    mState = STATE_RESET_IN_PROGRESS;
649    mPlayer->resetAsync();
650
651    while (mState == STATE_RESET_IN_PROGRESS) {
652        mCondition.wait(mLock);
653    }
654
655    mDurationUs = -1;
656    mPositionUs = -1;
657    mLooping = false;
658    mPlayingTimeUs = 0;
659
660    return OK;
661}

可以看到如果状态不对的话， 630 行返回 return INVALID_OPERATION;

这个定义 INVALID_OPERATION 为android::INVALID_OPERATION, 其文件路径为 system/core/include/utils/Errors.h

45enum {
46    OK                = 0,    // Everything's swell.
47    NO_ERROR          = 0,    // No errors.
48
49    UNKNOWN_ERROR       = (-2147483647-1), // INT32_MIN value
50
51    NO_MEMORY           = -ENOMEM,
52    INVALID_OPERATION   = -ENOSYS,
53    BAD_VALUE           = -EINVAL,
54    BAD_TYPE            = (UNKNOWN_ERROR + 1),
55    NAME_NOT_FOUND      = -ENOENT,
56    PERMISSION_DENIED   = -EPERM,
57    NO_INIT             = -ENODEV,
58    ALREADY_EXISTS      = -EEXIST,
59    DEAD_OBJECT         = -EPIPE,
60    FAILED_TRANSACTION  = (UNKNOWN_ERROR + 2),
61#if !defined(_WIN32)
62    BAD_INDEX           = -EOVERFLOW,
63    NOT_ENOUGH_DATA     = -ENODATA,
64    WOULD_BLOCK         = -EWOULDBLOCK,
65    TIMED_OUT           = -ETIMEDOUT,
66    UNKNOWN_TRANSACTION = -EBADMSG,
67#else
68    BAD_INDEX           = -E2BIG,
69    NOT_ENOUGH_DATA     = (UNKNOWN_ERROR + 3),
70    WOULD_BLOCK         = (UNKNOWN_ERROR + 4),
71    TIMED_OUT           = (UNKNOWN_ERROR + 5),
72    UNKNOWN_TRANSACTION = (UNKNOWN_ERROR + 6),
73#endif
74    FDS_NOT_ALLOWED     = (UNKNOWN_ERROR + 7),
75    UNEXPECTED_NULL     = (UNKNOWN_ERROR + 8),
76};

INVALID_OPERATION = -ENOSYS,

bionic/libc/kernel/uapi/asm-generic/errno.h

21#include <asm-generic/errno-base.h>
22#define EDEADLK 35
23#define ENAMETOOLONG 36
24#define ENOLCK 37
25#define ENOSYS 38
26#define ENOTEMPTY 39
27#define ELOOP 40
28#define EWOULDBLOCK EAGAIN
29#define ENOMSG 42
30#define EIDRM 43
31#define ECHRNG 44
32#define EL2NSYNC 45
33#define EL3HLT 46
34#define EL3RST 47
35#define ELNRNG 48
36#define EUNATCH 49
37#define ENOCSI 50
38#define EL2HLT 51
39#define EBADE 52
40#define EBADR 53
41#define EXFULL 54
42#define ENOANO 55
43#define EBADRQC 56
44#define EBADSLT 57
45#define EDEADLOCK EDEADLK
46#define EBFONT 59
47#define ENOSTR 60
48#define ENODATA 61
49#define ETIME 62
50#define ENOSR 63
51#define ENONET 64
52#define ENOPKG 65
53#define EREMOTE 66
54#define ENOLINK 67
55#define EADV 68
56#define ESRMNT 69
57#define ECOMM 70
58#define EPROTO 71
59#define EMULTIHOP 72
60#define EDOTDOT 73
61#define EBADMSG 74
62#define EOVERFLOW 75
63#define ENOTUNIQ 76
64#define EBADFD 77
65#define EREMCHG 78
66#define ELIBACC 79
67#define ELIBBAD 80
68#define ELIBSCN 81
69#define ELIBMAX 82
70#define ELIBEXEC 83
71#define EILSEQ 84
72#define ERESTART 85
73#define ESTRPIPE 86
74#define EUSERS 87
75#define ENOTSOCK 88
76#define EDESTADDRREQ 89
77#define EMSGSIZE 90
78#define EPROTOTYPE 91
79#define ENOPROTOOPT 92
80#define EPROTONOSUPPORT 93
81#define ESOCKTNOSUPPORT 94
82#define EOPNOTSUPP 95
83#define EPFNOSUPPORT 96
84#define EAFNOSUPPORT 97
85#define EADDRINUSE 98
86#define EADDRNOTAVAIL 99
87#define ENETDOWN 100
88#define ENETUNREACH 101
89#define ENETRESET 102
90#define ECONNABORTED 103
91#define ECONNRESET 104
92#define ENOBUFS 105
93#define EISCONN 106
94#define ENOTCONN 107
95#define ESHUTDOWN 108
96#define ETOOMANYREFS 109
97#define ETIMEDOUT 110
98#define ECONNREFUSED 111
99#define EHOSTDOWN 112
100#define EHOSTUNREACH 113
101#define EALREADY 114
102#define EINPROGRESS 115
103#define ESTALE 116
104#define EUCLEAN 117
105#define ENOTNAM 118
106#define ENAVAIL 119
107#define EISNAM 120
108#define EREMOTEIO 121
109#define EDQUOT 122
110#define ENOMEDIUM 123
111#define EMEDIUMTYPE 124
112#define ECANCELED 125
113#define ENOKEY 126
114#define EKEYEXPIRED 127
115#define EKEYREVOKED 128
116#define EKEYREJECTED 129
117#define EOWNERDEAD 130
118#define ENOTRECOVERABLE 131
119#define ERFKILL 132
120#define EHWPOISON 133
121#endif

这个值就是 -38，如果使用MediaPlayer 使用状态不对就会返回这个给上层