xpcom/sample/nsSample.cpp

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  22  * Contributor(s):
  23  *   Pierre Phaneuf <pp@ludusdesign.com>
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  38
  39
  40 /**
  41  *
  42  * A sample of XPConnect. This file contains an implementation nsSample
  43  * of the interface nsISample.
  44  *
  45  */
  46 #include <stdio.h>
  47
  48 #include "nsSample.h"
  49 #include "nsMemory.h"
  50
  51 #include "nsEmbedString.h"
  52 #include "nsIClassInfoImpl.h"
  53 ////////////////////////////////////////////////////////////////////////
  54
  55 nsSampleImpl::nsSampleImpl() : mValue(nsnull)
  56 {
  57     mValue = (char*)nsMemory::Clone("initial value", 14);
  58 }
  59
  60 nsSampleImpl::~nsSampleImpl()
  61 {
  62     if (mValue)
  63         nsMemory::Free(mValue);
  64 }
  65
  66 /**
  67  * NS_IMPL_ISUPPORTS1 expands to a simple implementation of the nsISupports
  68  * interface.  This includes a proper implementation of AddRef, Release,
  69  * and QueryInterface.  If this class supported more interfaces than just
  70  * nsISupports,
  71  * you could use NS_IMPL_ADDREF() and NS_IMPL_RELEASE() to take care of the
  72  * simple stuff, but you would have to create QueryInterface on your own.
  73  * nsSampleFactory.cpp is an example of this approach.
  74  * Notice that the second parameter to the macro is name of the interface, and
  75  * NOT the #defined IID.
  76  *
  77  * The _CI variant adds support for nsIClassInfo, which permits introspection
  78  * and interface flattening.
  79  */
  80 NS_IMPL_ISUPPORTS1_CI(nsSampleImpl, nsISample)
  81
  82 /**
  83  * Notice that in the protoype for this function, the NS_IMETHOD macro was
  84  * used to declare the return type.  For the implementation, the return
  85  * type is declared by NS_IMETHODIMP
  86  */
  87 NS_IMETHODIMP
  88 nsSampleImpl::GetValue(char** aValue)
  89 {
  90     NS_PRECONDITION(aValue != nsnull, "null ptr");
  91     if (! aValue)
  92         return NS_ERROR_NULL_POINTER;
  93
  94     if (mValue) {
  95         /**
  96          * GetValue's job is to return data known by an instance of
  97          * nsSampleImpl to the outside world.  If we  were to simply return
  98          * a pointer to data owned by this instance, and the client were to
  99          * free it, bad things would surely follow.
 100          * On the other hand, if we create a new copy of the data for our
 101          * client, and it turns out that client is implemented in JavaScript,
 102          * there would be no way to free the buffer.  The solution to the
 103          * buffer ownership problem is the nsMemory singleton.  Any buffer
 104          * returned by an XPCOM method should be allocated by the nsMemory.
 105          * This convention lets things like JavaScript reflection do their
 106          * job, and simplifies the way C++ clients deal with returned buffers.
 107          */
 108         *aValue = (char*) nsMemory::Clone(mValue, strlen(mValue) + 1);
 109         if (! *aValue)
 110             return NS_ERROR_NULL_POINTER;
 111     }
 112     else {
 113         *aValue = nsnull;
 114     }
 115     return NS_OK;
 116 }
 117
 118 NS_IMETHODIMP
 119 nsSampleImpl::SetValue(const char* aValue)
 120 {
 121     NS_PRECONDITION(aValue != nsnull, "null ptr");
 122     if (! aValue)
 123         return NS_ERROR_NULL_POINTER;
 124
 125     if (mValue) {
 126         nsMemory::Free(mValue);
 127     }
 128
 129     /**
 130      * Another buffer passing convention is that buffers passed INTO your
 131      * object ARE NOT YOURS.  Keep your hands off them, unless they are
 132      * declared "inout".  If you want to keep the value for posterity,
 133      * you will have to make a copy of it.
 134      */
 135     mValue = (char*) nsMemory::Clone(aValue, strlen(aValue) + 1);
 136     return NS_OK;
 137 }
 138
 139 NS_IMETHODIMP
 140 nsSampleImpl::Poke(const char* aValue)
 141 {
 142     return SetValue((char*) aValue);
 143 }
 144
 145
 146 static void GetStringValue(nsACString& aValue)
 147 {
 148     NS_CStringSetData(aValue, "GetValue");
 149 }
 150
 151 NS_IMETHODIMP
 152 nsSampleImpl::WriteValue(const char* aPrefix)
 153 {
 154     NS_PRECONDITION(aPrefix != nsnull, "null ptr");
 155     if (! aPrefix)
 156         return NS_ERROR_NULL_POINTER;
 157
 158     printf("%s %s\n", aPrefix, mValue);
 159
 160     // This next part illustrates the nsEmbedString:
 161     nsEmbedString foopy;
 162     foopy.Append(PRUnichar('f'));
 163     foopy.Append(PRUnichar('o'));
 164     foopy.Append(PRUnichar('o'));
 165     foopy.Append(PRUnichar('p'));
 166     foopy.Append(PRUnichar('y'));
 167
 168     const PRUnichar* f = foopy.get();
 169     PRUint32 l = foopy.Length();
 170     printf("%c%c%c%c%c %d\n", char(f[0]), char(f[1]), char(f[2]), char(f[3]), char(f[4]), l);
 171
 172     nsEmbedCString foopy2;
 173     GetStringValue(foopy2);
 174
 175     //foopy2.AppendLiteral("foopy");
 176     const char* f2 = foopy2.get();
 177     PRUint32 l2 = foopy2.Length();
 178
 179     printf("%s %d\n", f2, l2);
 180
 181     return NS_OK;
 182 }