update documentation

docs/sdk/core/app1.md

@@ -421,17 +421,13 @@ Here is the complete setup for App1:
 
 ```go
 func NewApp1(logger log.Logger, db dbm.DB) *bapp.BaseApp {
-    cdc := wire.NewCodec()
-
+	
     // Create the base application object.
-    app := bapp.NewBaseApp(app1Name, cdc, logger, db)
+    app := bapp.NewBaseApp(app1Name, logger, db, tx1Decoder)
 
     // Create a capability key for accessing the account store.
     keyAccount := sdk.NewKVStoreKey("acc")
 
-    // Determine how transactions are decoded.
-    app.SetTxDecoder(txDecoder)
-
     // Register message routes.
     // Note the handler receives the keyAccount and thus
     // gets access to the account store.

docs/sdk/core/app2.md

@@ -169,10 +169,19 @@ type app2Tx struct {
 func (tx app2Tx) GetMsgs() []sdk.Msg {
 	return []sdk.Msg{tx.Msg}
 }
-```
 
-We don't need a custom TxDecoder function anymore, since we're just using the
-Amino codec!
+// Amino decode app2Tx. Capable of decoding both MsgSend and MsgIssue
+func tx2Decoder(cdc *wire.Codec) sdk.TxDecoder {
+	return func(txBytes []byte) (sdk.Tx, sdk.Error) {
+		var tx app2Tx
+		err := cdc.UnmarshalBinary(txBytes, &tx)
+		if err != nil {
+			return nil, sdk.ErrTxDecode(err.Error())
+		}
+		return tx, nil
+	}
+}
+```
 
 ## AnteHandler
 
@@ -249,7 +258,7 @@ func NewApp2(logger log.Logger, db dbm.DB) *bapp.BaseApp {
 	cdc := NewCodec()
 
 	// Create the base application object.
-	app := bapp.NewBaseApp(app2Name, cdc, logger, db)
+	app := bapp.NewBaseApp(app2Name, logger, db, txDecoder(cdc))
 
 	// Create a key for accessing the account store.
 	keyAccount := sdk.NewKVStoreKey("acc")
@@ -280,9 +289,8 @@ key for a second store that is *only* passed to a second handler, the
 `handleMsgIssue`. The first `handleMsgSend` has no access to this second store and cannot read or write to
 it, ensuring a strong separation of concerns.
 
-Note also that we do not need to use `SetTxDecoder` here - now that we're using
-Amino, we simply create a codec, register our types on the codec, and pass the
-codec into `NewBaseApp`. The SDK takes care of the rest for us!
+Note now that we're using Amino, we create a codec, register our types on the codec, and pass the
+codec into our TxDecoder constructor, `tx2Decoder`. The SDK takes care of the rest for us!
 
 ## Conclusion
 

docs/sdk/core/app3.md

@@ -328,7 +328,7 @@ func NewApp3(logger log.Logger, db dbm.DB) *bapp.BaseApp {
 	cdc := NewCodec()
 
 	// Create the base application object.
-	app := bapp.NewBaseApp(app3Name, cdc, logger, db)
+	app := bapp.NewBaseApp(app3Name, logger, db, auth.DefaultTxDecoder(cdc))
 
 	// Create a key for accessing the account store.
 	keyAccount := sdk.NewKVStoreKey("acc")
@@ -361,6 +361,9 @@ and receives only the `bank.Keeper`. See the
 [x/bank API docs](https://godoc.org/github.com/cosmos/cosmos-sdk/x/bank)
 for more details.
 
+We also use the default txDecoder in `x/auth`, which decodes amino-encoded
+`auth.StdTx` transactions.
+
 ## Conclusion
 
 Armed with native modules for authentication and coin transfer,