BLE Android write characteristic data

Question

I am working on a BLE project using Android. I want to write characteristic data and send it to a BLE chip.

I want to rewrite ISEN_Toulon

I used this code to write characteristic data, but data "ISEN_Toulon" isn't replaced by "TEST" as expected.

private BluetoothGattCharacteristic mWriteCharacteristic;

private final ExpandableListView.OnChildClickListener servicesListClickListner =
        new ExpandableListView.OnChildClickListener()
        {
            @Override
            public boolean onChildClick(ExpandableListView parent, View v, int groupPosition,int childPosition, long id)
            {
                if (mGattCharacteristics != null) {
                    final BluetoothGattCharacteristic characteristic = mGattCharacteristics.get(groupPosition).get(childPosition);
                    final int charaProp = characteristic.getProperties();
.....
                    // READ
                    if ((charaProp | BluetoothGattCharacteristic.PROPERTY_READ) > 0) {
                        // If there is an active notification on a characteristic, clear
                        // it first so it doesn't update the data field on the user interface.
                        if (mNotifyCharacteristic != null) {
                            mBluetoothLeService.setCharacteristicNotification(
                                    mNotifyCharacteristic, false);
                            mNotifyCharacteristic = null;
                        }
                        mBluetoothLeService.readCharacteristic(characteristic);
                        Log.d("myTag", "1");
                    }
                    // NOTIFY
                    if ((charaProp | BluetoothGattCharacteristic.PROPERTY_NOTIFY) > 0) {
                        mNotifyCharacteristic = characteristic;
                        mBluetoothLeService.setCharacteristicNotification(
                                characteristic, true);
                        Log.d("myTag", "2");
                    }

                    // WRITE  
                    characteristic.setWriteType(BluetoothGattCharacteristic.PROPERTY_WRITE);
                    characteristic.setWriteType(BluetoothGattCharacteristic.WRITE_TYPE_NO_RESPONSE);
                    characteristic.setWriteType(BluetoothGattCharacteristic.PROPERTY_WRITE_NO_RESPONSE);

                    mWriteCharacteristic = characteristic;

                    String str = "TEST";
                    byte[] strBytes = str.getBytes();
                    characteristic.setValue(strBytes);
                    writeCharacteristic(characteristic)

                    return true;
                }
                return false;
            }
};

Where do you read the value back in? Is that in your adapter code? if so, please post. — rothloup, Feb 17 '16 at 03:40
@rothloup I edited my post and I added the `READ` part of the code. — Johnrednex, Feb 19 '16 at 07:37
@Johnrednex well, you appear to read before your write, so that might be your issue. In any case, I think you need to do a better job of explaining exactly what the problem is. What piece of code isn't working? no one is going to pick apart your code - you need to remove everything that is irrelevant and keep all relevant context. Show your expected result, and your actual result, and related code. nothing more, nothing less. [See more here](http://stackoverflow.com/help/mcve) — rothloup, Feb 19 '16 at 14:32
you can find an implementation for the write method in this project: https://github.com/Fakher-Hakim/android-BluetoothLeGatt — Fakher, Mar 07 '16 at 10:22
Thank you but the issue was solved long time ago. It was the ble chip authorizations not set properly. — Johnrednex, May 11 '16 at 19:59

score 2 · Answer 1 · answered May 10 '16 at 16:44

I have encountered the same problem with you. The detail way to solve the problem I do not remember. But I have a code to write BLE characteristics to BLE devices like this:(at least it works for me)

    public OnClickListener clickListener = new OnClickListener() {

    @Override
    public void onClick(View arg0) {
        // TODO Auto-generated method stub
        if (mGattCharacteristics != null) {
            if(charas.size()>=6){
                BluetoothGattCharacteristic characteristic =
                        charas.get(0);
                BluetoothGattCharacteristic characteristic_write = charas.get(5);
                int charaProp_write = characteristic_write.getProperties();
                int charaProp = characteristic.getProperties();
                //String getUUID = characteristic.getUuid().toString();
                if (((charaProp_write | BluetoothGattCharacteristic.PROPERTY_WRITE) > 0)
                        &&  
                        (characteristic_write != null)){

                    if (mNotifyCharacteristic != null) {
                        mBluetoothLeService.setCharacteristicNotification(
                                mNotifyCharacteristic, false);
                        mNotifyCharacteristic = null;
                    }   
                    byte[] writev = new byte[SIMPLEPROFILE_CHAR6_LEN];
                    Arrays.fill(writev, (byte)'0');
                    byte[] getedit1 = edit1.getText().toString().getBytes();//edit1.getText().toString().getBytes();
                    byte[] getedit2 = edit2.getText().toString().getBytes();
                    byte[] getedit3 = edit3.getText().toString().getBytes();


                    //System.out.println(getedit1 + " " + getedit2 + " " + getedit3);

                    if ((getedit1.length + getedit2.length + getedit3.length) <= (max_syvlength+max_spvlength+max_tuvlength)) {
                        //this 'if' can be canceled
                        writev[0] = (byte)'1';
                        writev[1] = (byte)(getedit1.length);
                        writev[2] = (byte)(getedit2.length);
                        writev[3] = (byte)(getedit3.length);
                        System.arraycopy(getedit1, 0, writev, 4, getedit1.length);
                        System.arraycopy(getedit2, 0, writev, 4 + getedit1.length, getedit2.length);
                        System.arraycopy(getedit3, 0, writev, 4 + getedit1.length + getedit2.length, getedit3.length);
                        writev[4 + getedit1.length + getedit2.length + getedit3.length] = '@';
                    }

                    /*
                    for(int i = 0;i<15;i++){
                        Log.d(TAG, "is:" + writev[i]);
                    }
                    */                      

                    characteristic_write.setValue(writev);
                    characteristic_write.setWriteType(BluetoothGattCharacteristic.WRITE_TYPE_NO_RESPONSE);
                    mBluetoothLeService.writeCharacteristic(characteristic_write);

                }
                if ((charaProp | BluetoothGattCharacteristic.PROPERTY_READ) > 0) {
                    // If there is an active notification on a characteristic, clear
                    // it first so it doesn't update the data field on the user interface.
                    if (mNotifyCharacteristic != null) {
                        mBluetoothLeService.setCharacteristicNotification(
                                mNotifyCharacteristic, false);
                        mNotifyCharacteristic = null;
                    }
                    mBluetoothLeService.readCharacteristic(characteristic);

                }       
                if ((charaProp | BluetoothGattCharacteristic.PROPERTY_NOTIFY) > 0) {
                    mNotifyCharacteristic = characteristic;
                    mBluetoothLeService.setCharacteristicNotification(
                            characteristic, true);
                }

            }
        }

        GotoMyActivity();

    }
};

score 2 · Answer 2 · edited Sep 04 '19 at 10:16

I know this is old, but as I had a similar issue today, others might like an answer.

The issue it that you set the WriteType 3 times - effectually overwriting the two first values set. Your code:

...
characteristic.setWriteType(BluetoothGattCharacteristic.PROPERTY_WRITE);
characteristic.setWriteType(BluetoothGattCharacteristic.WRITE_TYPE_NO_RESPONSE);
characteristic.setWriteType(BluetoothGattCharacteristic.PROPERTY_WRITE_NO_RESPONSE);

Two issues:

The values starting with PROPERTY_ are not write types, hence only WRITE_TYPE_NO_RESPONSE is valid
The third call to setWriteType() overwrites the valid value with an invalid value, and the Android stack then ignores your write request.

Unless there is a specific reason to use WRITE_NO_RESPONSE, you should use a normal write (WRITE_TYPE_DEFAULT). The Android stack sometimes miss a write - as in the application do call write for example 5 times, but only 1 or 2 of the writes are send over air. This is even when the onCharacteristicWrite() callback reports success.

characteristic.setWriteType(BluetoothGattCharacteristic.WRITE_TYPE_DEFAULT);

score 1 · Answer 3 · answered Aug 20 '19 at 10:06

1

Your case is of writing multiple bytes of data to the characteristic to bluetooth device, which has few rules:

Android can not write parallel data packets to the ble device.
The data should not exceed 20 bytes
You should divide the data to chunks and send to ble device
You should wait for the write callback onCharacteristicWrite() before sending next data packet to be written to the ble device.

answered Aug 20 '19 at 10:06

Vipul

96
6

1

"The data should not exceed 20 bytes" should be "The data should not exceed 20 bytes unless the MTU has been increased, or the remote device supports Long Writes". – Emil Aug 20 '19 at 11:45

score 0 · Answer 4 · answered Apr 24 '19 at 15:39

Trying to override callback function in

BluetoothGattCallback mGattCallback = new BluetoothGattCallback(){
//something callback function like:

@Override
        public void onConnectionStateChange(BluetoothGatt gatt, int status, int newState) {
      //do something read/write
}

You need to figure out how BLE callback function work!!! Check this out.

Because BLE write/read can only be done in one time. It's mean that if I read a data from characteristic. I can only do another write/read action after previous one done.

BLE Android write characteristic data

4 Answers4

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